EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 1 Effects of Residential Gas
Appliances on Indoor and
Outdoor Air Quality and
Public Health in California
UCLA Fielding School of Public Health
Department of Environmental Health Sciences
April 2020
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA ii
AUTHORS
Dr. Yifang Zhu (Principal Investigator)
Rachel Connolly
Dr. Yan Lin
Timothy Mathews
Zemin Wang
Agreement Number 20184996
Cover: A view of downtown Los Angeles from
Hollywood Hills, blanketed in smog the afternoon
of March 5th, 2020. Photo by Kristiana Faddoul,
Sierra Club
ACKNOWLEDGEMENTS
The authors wish to acknowledge:
Nick Dirr Association for Energy Affordability • Adam Stern (consultant) Bay Area Air Quality Management District • Qunfang “Zoe” Zhang California Air Resources Board • Kevin Hamilton Central California Asthma Collaborative • Zoe Chafe C40 Cities • Claire Broome Emory University School of Public Health • Isaac Sevier Energy Efficiency for All • Carmelita Miller Greenlining Institute • Thomas Phillips Healthy Building Research • Arjun Makhijani Institute for Energy and Environmental Research • Brett Singer, Richard Sextro (retired) Lawrence Berkeley National Laboratory • Pierre Delforge Natural Resources Defense Council • Andee Krasner Physicians for Social Responsibility • Sean Armstrong Redwood Energy • Brady Seals Rocky Mountain Institute • Rachel Boyer, Kristiana Faddoul, Rachel Golden, Peter Walbridge, Thomas Young Sierra Club• Gregory Pierce UCLA Luskin Center for Innovation The report was prepared for the Sierra Club. The views, opinions, findings, and conclusions or recommendations expressed in this report are strictly those of the authors. They do not necessarily reflect the views of the Sierra Club and/or authors’ affiliated institutes.
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA iii
TABLE OF CONTENTS
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii List of Tables and Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv Abbreviations and Units List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.1. California’s Gas Consumption and Transition to Clean Energy . . . . . . . . . . . . . . . . . . . . 8
1.2. Gas Appliance Use and Associated Air Quality and Health Outcomes . . . . . . . . . . . . . 9
1.3. Scope of Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2 Indoor Air Quality and Health Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.1. Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2. Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 3 Outdoor Air Quality and Health Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.1. Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.2. Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Appendices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Appendix A: Data and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 A .1. Indoor Air Quality & Health Effects (Section 2 in the report) . . . . . . . . . . . . . . . . . . . . 42 A .1.1. Emission factor database . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 A .1.2. Indoor air quality impacts and susceptibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 A .1.3. Health effects of air pollution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 A .2. Outdoor Air Quality & Health Effects (Section 3 in the report) . . . . . . . . . . . . . . . . . . 45 A .2.1. Contribution to total emissions of outdoor air pollutants in California . . . . . . 45 A .2.2. Emission reduction due to electrification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 A .2.3. Reduced ambient PM2.5 concentrations and resulting mortality and morbidity impacts due to electrification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Appendix B: Supplemental Figures and Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA iv
LIST OF TABLE AND FIGURES
TABLES
Indoor Air Quality Analysis
Table 2-1: Mean emission factors (EF) and emission rates (ER) for each appliance type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Table 2-2: Average indoor air concentrations by appliance — peak (highest concentration) vs . time-averaged 15-minute cooking, 1-hour cooking, and 2-hour cooking scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Table 2-3: Concentration and exposure scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Table 2-4: Percent exceedances of air quality thresholds by appliances used and cooking time intervals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 Table 2-5: Average peak (kitchen) and time-weighted, 8-hour average (entire home) CO concentrations from use of gas kitchen appliances in various residence types, and percentage of scenarios in which concentrations exceed air quality thresholds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Table 2-6: Average peak (kitchen) and time-weighted 24-hour average (entire home) NO2 concentrations from use of gas kitchen appliances in various residence types, and percentage of scenarios in which concentrations exceed air quality thresholds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 Table 2-7: Mean peak CO and NO2 exposures in the entire home associated with pollutant backdrafting/spillage and various capture efficiencies . . . . . . 23 Table 2-8: Overview of health effects of main studied pollutants . . . . . . . . . . . . . . . . . . . . . 26 Outdoor Air Quality Analysis
Table 3-1: Annual health impacts and monetized benefits from outdoor air quality improvements in a residential electrification scenario . . . . . . . . . . . . . . . . . . . . . 39 Table 3-2: Estimated annual monetization of health benefits from the electrification scenario by air basin for the five air basins with the highest benefits throughout the state . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
FIGURES
Indoor Air Quality Analysis
Figure 2-1: Peak concentrations in the kitchen resulting from usage of stoves and ovens simultaneously, by pollutant [(a) CO and (b) NO2] and housing type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Outdoor Air Quality Analysis
Figure 3-1: Estimated state-wide emissions of pollutants (a) CO, (b) NO2, and (c) NOX by gas appliance type . . . . . . . . . . . . . . . . . . . . . . . 36 Figure 3-2: Estimated emissions of (a) CO, (b) NO2, and (c) NOX in air basins from gas appliances by type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Figure 3-3: Total reduction in ambient PM2.5 concentrations in California from elimination of gas appliances, by county in 2018. . . . . . . . 38 Figure 3-4: Total reduction in annual cases of PM2.5 related all-cause mortality by county in 2018. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA v
ABBREVIATIONS AND UNITS LIST
ABBREVIATIONS/
ACRONYMS
DESCRIPTIONS*
AB Assembly Bill
ACS American Community Survey
AER Air exchange rate
AHS American Housing Survey
BenMAP U .S . EPA’s Benefits Mapping and
Analysis tool
BTU British thermal unit
CAAQS California Ambient Air Quality
Standards
CARB California Air Resources Board
CDC Centers for Disease Control and
Prevention
CEC California Energy Commission
CH4 Methane
CO Carbon monoxide
CO2 Carbon dioxide
COPD Chronic Obstructive Pulmonary
Disease
DTSC California Department of Toxic
Substances Control
E3 Energy and Environmental Economics,
Inc .
EF Emission factor
EPRI Electric Power Research Institute
GHG Greenhouse gas
h Hour
HHRA Human Health Risk Assessment
HQ Hazard Quotient
I/O Indoor/outdoor ratio
IARC International Agency for Research on
Cancer
ISA Integrated Science Assessment
J Joule
LBNL Lawrence Berkeley National Laboratory
ABBREVIATIONS/
ACRONYMS
DESCRIPTIONS*
MBR Mass burning rate
mg Milligram
ng Nanogram
NAAQS National Ambient Air Quality Standards
NO Nitric oxide
NO2 Nitrogen dioxide
NOX Nitrogen oxides
µg Microgram
OEHHA Office of Environmental Health Hazard
Assessment
ppb parts per billion
ppm parts per million
PAH Polycyclic aromatic hydrocarbon
PERE Program for Environmental and
Regional Equity
PM Particulate matter
PM2.5 Fine particulate matter
PN Particle number
RASS Residential Appliance Saturation Study
REL Reference Exposure Level
SB Senate Bill
SFH Single-family home
SO2 Sulfur dioxide
UCI University of California, Irvine
USC University of Southern California
UFP Ultrafine particle
US EPA United States Environmental
Protection Agency
VOC Volatile organic compound
VSL Value of a statistical life
WHO World Health Organization
WTP Willingness to pay
* Links to the associated databases are embedded wherever applicable.
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 6 EXECUTIVE SUMMARY
The electrification of residential buildings refers to the transition from fossil-fuel-powered appliances to electric technologies. Dozens of cities in California have already passed electrification policies to ensure new constructions within their jurisdictions are built all-electric. State regulatory agencies and utilities are pursuing programs and policies to support residential and commercial building electrification as part of meeting the state’s climate and energy goals.
There has been considerable focus on building
electrification’s potential to reduce greenhouse gas
emissions, and less focus on how electrification can also yield significant air quality and public health benefits .
California currently faces a global pandemic in which a rapidly spreading coronavirus disease, COVID-19, can
cause severe respiratory illness and even death . New
evidence suggests that a small increase in long-term
exposure to fine particulate matter (PM2.5 ) leads to a large increase in the COVID-19 death rate; this further establishes the substantial value in protecting the
population from the respiratory vulnerability caused by widespread air pollution .
Exposure to the pollutants produced from gas appliances can be detrimental to human health; thus, one significant benefit of replacing natural gas (hereafter referred to as “gas”) appliances with electric appliances would
be the elimination of indoor air pollution that comes
from burning gas indoors . This report aims to better
understand the health concerns associated with gas
appliance use, as well as the health benefits of phasing out residential gas appliances in California .
To systematically evaluate the impact of gas appliances on indoor air quality (Section 2), we developed an emis- sion factor (EF) database, provided an estimate of indoor air pollutant concentrations due to gas appliance usage, and characterized the associated health impacts . Next, we evaluated the potential health co-benefits resulting from changes to ambient (outdoor) air quality related to resi- dential gas appliance electrification (Section 3) . This was accomplished by estimating the total emission of outdoor air pollutants in California due to the use of household gas appliances, the reduction in emissions due to residential building electrification under a modeled transition scenar- io, the resulting reduction of premature deaths and cases of acute and chronic bronchitis in California, and moneti- zation of those health benefits . A detailed description of the data and methods can be found in Appendix A .
Key Findings
INDOOR AIR QUALITY
• Gas appliances emit a wide range of air pollutants,
such as carbon monoxide (CO), nitrogen oxides (NOx,
including nitrogen dioxide (NO2)), particulate matter
(PM), and formaldehyde, which have been linked to
various acute and chronic health effects, including
respiratory illness, cardiovascular disease, and
premature death .
• Under a hypothetical cooking scenario where a
stove and oven are used simultaneously for 1 hour,
peak concentrations of NO2 from cooking with gas
appliances exceed the levels of acute national and
California-based ambient air quality thresholds in
more than 90% of modeled emission scenarios .
• Concentrations of CO and NO2 resulting from gas
cooking are the highest for apartments, due to a smaller residence size . This presents an additional risk for
renters, who are often low-income .
• Increases in indoor air pollutant concentrations can be driven by insufficient ventilation . Surveys show that less than 35% of California residents use range hoods when
cooking — and many homes in the U .S . are lacking range hoods or ventilation altogether .
• The use of kitchen appliances for supplemental heating can increase exposure risks, and there is evidence this disproportionately affects low-income households,
though more data on the frequency of use is needed to
quantify the risk to various populations .
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 7 • Environmental justice communities disproportionately experience poor housing conditions which can be
detrimental to health . Concerns related to gas appliance use include: the presence of old and unmaintained
appliances in households, smaller and overcrowded
residences where air pollution can reach higher
concentrations, and challenges faced by renters to
control appliance choices or afford maintenance . These populations already face cumulative effects associated
with health and environmental injustices more broadly,
and gas appliance issues can compound this . There are
significant data gaps regarding equity and the health
effects of gas combustion on low-income and minority
populations, which should be further explored to
facilitate a just transition to a low-carbon future .
• Better regulations and safeguards are needed to protect residents from exposure to indoor air pollution from gas appliances . Along with replacing gas kitchen appliances with electric alternatives, increasing the frequency of range hood use and improving the efficacy of ventilation technology would also reduce exposure and protect
public health .
OUTDOOR AIR QUALITY
• Gas appliances are also a source of outdoor air pollution, and literature shows that the pollutants released by
combustion can lead to illness and premature death .
• Using the EFs developed in this study’s indoor air
quality analysis, and assuming all indoor emissions are transported to the outdoor environment, we find that
approximately 12,000 tons of CO and 15,900 tons of
NOX (see Figure 3-1 in Section 3 .2 .1) were emitted to outdoor air from the use of residential gas appliances in California in 2018 .
• If all residential gas appliances were immediately
replaced with clean electric alternatives, the reduction of outdoor NOX and PM2.5 would result in 354
fewer deaths, as well as 596 fewer cases of acute
bronchitis and 304 fewer cases of chronic bronchitis
annually in California (Table 3-1) . This is equivalent to approximately $3 .5 billion in monetized health benefits over the course of one year . These numbers only
account for exposures from outdoor air as a result of
residential electrification; a full exposure assessment accounting for indoor exposures would increase the
total health benefits and the associated economic
benefits of residential electrification .
In summary, this report contributes to a growing body of research quantifying the air quality and health impacts from the use of gas appliances in households, and
highlights several potential benefits, both health-related and economic, of residential electrification throughout the state of California . While this report provides
an estimate of emissions, and resulting emission
reductions from discontinuing the use of gas appliances in residences, it does not consider the full spectrum
of costs and benefits associated with residential
building electrification . Policymakers and stakeholders are encouraged to use this report, alongside existing
research on building decarbonization, electrification,
and other related topics, as a tool to develop stronger regulations and protections that limit indoor and outdoor air pollution from gas appliances, and to support new
policy development to improve public health, particularly for communities disproportionately burdened by
pollution from fossil fuels .
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 8 1 INTRODUCTION
i. Though gas has been considered a transitional fuel because it emits less GHGs than other fossil fuels 10, evidence indicates that the leakage of methane negates the climate benefits of burning gas. 11 In addition, the use of fracking for the extraction of gas results in methane leaks and incurs severe environmental and health costs; the chemical additives involved in fracking are highly toxic. 11–13
1.1. CALIFORNIA’S GAS CONSUMPTION
AND TRANSITION TO CLEAN ENERGY
Natural gas (hereafter referred to as “gas”) is one of
California’s primary energy sources .1 It is a fossil fuel consisting of mostly hydrocarbons, the majority of which is methane (CH4) - a potent greenhouse gas (GHG) .
In 2018, more than 2 .1 trillion cubic feet of gas were consumed in California, which accounts for 7 .1% of gas consumption within the entire United States .1
In California, gas is used to fuel power plants and certain industrial processes, and in buildings for heating and
cooking . In residences, common gas-powered appliances
include stoves, ovens, furnaces, water heaters, clothes dryers, and fireplaces . Results from the American
Housing Survey (AHS) indicate that more than 90% of
California households use gas for at least one purpose, and almost 70% of households use gas for cooking .2
While demand for gas in the power sector is expected
to drop dramatically as the state implements Senate Bill (SB) 100, which calls for 100% carbon-free electricity, there is no current statewide policy to address the
gas that is burned inside California’s buildings, even
though consumption by residential and commercial
buildings accounts for 31% of gas use within the state .1 The residential sector alone accounts for more than
20% of the state’s gas use .1 Research also indicates
that residential appliances alone constitute 15% of
California’s CH4 emissions from gas,3 and overall,
buildings are responsible for an estimated 25% of all
GHG emissions in California .4,5 Two-thirds of these are caused by onsite combustion of fuel, including gas .5
While this report focuses on California, it is worth noting that the climate effects of gas use in buildings are of national significance . The United States Environmental Protection Agency (US EPA) reported that in 2017,
gas consumption comprised 89% of direct, fossil-fuel
carbon dioxide (CO2) emissions from the residential and commercial sectors .6
California is a national leader in clean energy and
climate policy, and has mainly pursued new policies and programs to promote building electrification (i .e ., the transition from fossil-fuel-powered appliances to electric technologies) as a climate mitigation strategy .4,7,8 State and local agencies have not, for the most part, regulated gas appliances or promoted electrification to explicitly improve air quality and public health, although agencies and reports have noted cleaner air and improved health
outcomes as a co-benefit of building decarbonization .9 This research was commissioned to inform the potential
air quality and health benefits of stricter regulation of gas appliances with a goal of improving the state’s air quality and population health, and to better understand the co- benefits of building decarbonization .
Much recent research surrounding the use of gas as
an energy source focuses on emissions of GHGs, such
as carbon dioxide (CO2) as a result of combustion, as
well as the leakagei of CH4 .3,14 Organizations such as Energy and Environmental Economics, Inc . (E3) and
the Electric Power Research Institute (EPRI) have
conducted comprehensive research for the California
Energy Commission (CEC) and utility companies on
decarbonization and building electrification . Findings indicate that California residential building electrification is a cost-effective GHG mitigation tool under many
circumstances, and would often result in reduced
consumer household energy costs .4,7
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 9 1.2. GAS APPLIANCE USE AND
ASSOCIATED AIR QUALITY AND
HEALTH OUTCOMES
Another key area in the literature explores the extent
of criteria pollutants, such as carbon monoxide (CO),
nitrogen dioxide (NO2), and particulate matter (PM)
produced from gas combustion, and the health co-
benefits from GHG reduction tactics due to the reduction of these criteria air pollutants, which have a more
localized and substantial impact on public health than
GHGs .15 Gas has been marketed as a relatively clean fuel because it emits less criteria pollutants compared to
other fossil fuels, such as coal and oil,16,17 as well as the burning of biomass .18,19 However, there are significant risks associated with the burning of gas in residences, due to the indoor emission of pollutants, such as CO
and formaldehyde (from incomplete combustion), as
well as nitrogen oxides (NOX) such as NO2 (caused by
the oxidation of nitrogen during combustion) . Other
hazardous compounds emitted from the burning of
gas inside homes include volatile organic compounds
(VOCs), sulfur oxides, and PM .20 The resulting indoor air pollution can have adverse effects on human health, as
Americans spend almost 90% of their time indoors, 21
and a substantial body of literature has established that both indoor and outdoor air pollution are notable threats to human health .22–24 While many studies have been
published on the various sources and effects of indoor air pollution, the extent of the effects of residential exposure to combusted gas on human health merits additional
analysis .
Many studies have measured emissions and
concentration levels of NO2, NOX, PM, formaldehyde,
and other compounds while appliances were in use .
Overall, studies have reported higher concentrations
of CO and NO2 in homes that use gas rather than all-
electric appliances . Although electric appliances do not generate emissions from combustion, they can produce
emissions from other sources, such as the cooking of
food, or dust on the heating surface .23,25–28 There are also numerous studies on cooking activities, which
also provide evidence of emissions from gas stove and
oven use, although some emissions are related to the
cooking style and type of food being cooked, and not
the fuel that is being used .26,28,29 Additionally, studies on the association between gas appliance use and
health have mixed results, in part due to study design
limitations, but also due to a lack of data on quantified exposures .30,31 The nature of this uncertainty is
described in further detail in Section 2 .1 . Studies have also demonstrated associations between gas stove
use and increased respiratory symptoms for household
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 10 residents, particularly children .32–34 Notably, children had lower odds of suffering from asthma and bronchitis in
households where adults used ventilation when operating gas stoves .35 The California Department of Public Health recommends increasing outdoor ventilation and using
exhaust fans when cooking with gas stoves, and avoiding the use of illegal, fuel-burning, unvented gas space
heaters .36
Environmental health burdens associated with gas
appliance use can disproportionately affect low-income
individuals, who are often renters with less control over appliance installation and maintenance,37–39 and typically living in smaller units, which can result in elevated
pollutant concentrations .40,41 These issues compound
the cumulative health effects in environmental justice
communities, populations which currently — and
historically — have borne a disproportionate burden of
environmental health risks .
1.3. SCOPE OF RESEARCH
Considering existing knowledge, as well as specific
knowledge gaps, this research builds upon work from
other organizations, including the Lawrence Berkeley
National Laboratory (LBNL), the California Air Resources Board (CARB), the CEC, E3, and EPRI, to conduct a wide- ranging evaluation of the effects of gas appliance use
on both indoor and outdoor air quality, the associated
health effects and susceptibility of populations, and
the potential benefits of electrifying residential gas
appliances throughout the state . We endeavor to
consider how these issues impact low-income and
environmental justice communities throughout the
report .
This report is a synthesis of relevant literature and
data, incorporating literature primarily focused on the 21st century in California, and including new secondary analyses and modeling to the extent possible . Our
work is novel in its combination of varying approaches
of evaluating gas appliances, including: (1) modeling
a variety of gas cooking exposure scenarios and
conducting sensitivity analyses accounting for pollutant spillage into the indoor environment from four types
of appliances; (2) an evaluation of exposure and
vulnerability considerations, including equity-related
concerns associated with gas appliance use; (3) an in-
depth aggregation of current data on the health impacts of pollutants associated with gas combustion; (4) a
quantitative assessment of outdoor emissions resulting
from gas appliance use; and (5) a health impact and
monetary valuation assessment of exposure to those
outdoor emissions . This assessment aims to help the
general public and policymakers to better understand the potential health impacts associated with gas appliance
use, as well as the health benefits of phasing out
residential gas appliances in California .
In the rest of the report, we separate our analysis into two main sections: indoor air quality and health effects, and outdoor air quality and health effects . We start with a detailed background section, then present results
and discussion for each section . We conclude with a
summary of our findings . The data and methodology can
be found in Appendix A .
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 11 2 INDOOR AIR QUALITY AND HEALTH
EFFECTS
Section 2 is focused on indoor air quality and health effects. Section 2.1 provides background information from a literature review, and Section 2.2 contains the results and discussion. The objectives of this section are to:
• quantify emission factors of CO, NO2, and NOX from gas appliances in California; • evaluate the impact of gas appliance usage on indoor levels of CO, NO2, and NOX, as well as their associated health effects; and
• qualitatively assess the vulnerability of specific populations to indoor air pollution exposures from gas appliance usage, through an equity lens.
In this section of the report, we quantitatively focus
on three pollutants: CO, NO2, and NOX . We do not
include other pollutants, such as formaldehyde and PM
[including ultrafine particles (UFP, particles less than 0 .1 micrometer in size), and fine PM with an aerodynamic
diameter less than or equal to 2 .5 micrometers (PM2.5)], due to data paucity and feasibility . However, to the extent possible, we do qualitatively assess the emissions and
associated health effects of these additional pollutants .
Therefore, formaldehyde and PM are mentioned
throughout the background (Section 2 .1), and exposure is assessed in various portions of the Results & Discussion (Section 2 .2) .
2.1. BACKGROUND
This section provides general background information
from the literature, and further findings based on
modeling are presented in the results section . In this literature review section, we:
• explore the relationship between gas appliance use and indoor air quality by describing findings from relevant research studies and reports (2 .1 .1);
• define factors associated with pollutant emissions
(2 .1 .2) and resulting indoor air concentrations (2 .1 .3), such as appliance ventilation and maintenance, and
house volume and air exchange rate (AER);
• clarify the significance of the relationship between
indoor air pollution and human health, particularly with respect to environmental justice communities (2 .1 .4); and
• identify current knowledge gaps and the contribution of this report (2 .1 .5) .
2.1.1. THE RELATIONSHIP BETWEEN GAS
APPLIANCE USE AND INDOOR AIR QUALITY
Formation of combustion pollutants
Combustion pollutants are produced from the use of
gas appliances, including water heaters, stoves, ovens, furnaces and other indoor heating devices, such as gas
fireplaces . Notable pollutants include CO, NO2, NOX,
formaldehyde, and PM, including UFP and PM2.5 , though
there are several other pollutants associated with
residential gas combustion (see Table B-1 in Appendix
B regarding pollutants emitted from gas combustion
and their associated concentrations in the indoor
environment) . Although we were unable to quantitatively analyze all the pollutants emitted by combustion
appliances, Table B-1 illustrates the wide range of
pollutants produced . It excludes the pollutants subjected to subsequent quantitative analysis in this report — CO, NO2, and NOX — pollutants with known health effects
that also have enough publicly available combustion
emission data to conduct analysis .
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 12 Combustion-related pollutants are primarily formed by the processes of incomplete combustion or oxidation .
Incomplete combustion occurs when there is insufficient oxygen available to complete the combustion of fuel,
resulting in byproducts such as CO and formaldehyde .
In order to facilitate “complete” combustion, the proper amount of gas and air must be supplied at the correct
pressure . However, incomplete combustion and its
associated byproducts are unavoidable, even under
ideal conditions .42 Regarding oxidation, a prevalent
example resulting in combustion pollution formation
is the oxidation of nitric oxide (NO) to NO2 . At high
temperatures, NO is formed by the combination of
nitrogen with oxygen then oxidized to become NO2 .
Overview of types of gas appliances
Out of all commonly used gas appliances, water
heaters and home heating devices such as furnaces are
responsible for the majority of gas use in households, and thus, emit a larger proportion of combustion pollutants than gas kitchen appliances (stoves and ovens) .3,15,42–44 However, kitchen appliance emissions have a more
significant effect on indoor air quality, as the heating appliances are vented outdoors and those emissions are
generally considered to be outside the building envelope .
Depending on the type of appliance and associated
features, pollutants are either emitted directly into the living space, mitigated with ventilation technology such as range hoods, or directly vented outdoors (typically
water heaters and furnaces) . Ventilation effectiveness, which usually depends on appliance quality and
maintenance, is discussed further in Section 2 .1 .2 . There are regulations surrounding the use of gas appliances in households, including requirements for heating devices
and water heaters to be vented outdoors, and prohibiting the sale of unvented gas space heaters . We discuss
these regulations further in Section 2 .1 .2 .
Pollutant emissions and indoor air concentrations
associated with gas appliance use
Organizations such as LBNL and CARB have conducted
research on the topic of gas appliance emissions
in California specifically . They have studied the
effectiveness of ventilation technology (including the
use of range hoods), issues such as backdrafting (the
backward movement of exhausted gases through
the venting system) into residences from ventilation
ducts and pollutant spillage (described in more detail
in Section 2 .1 .2), and increasing the energy efficiency of appliances, and have modeled indoor air quality and
population exposures resulting from the use of these
appliances . 27,4 4–53 Additionally, researchers from other institutions have conducted various studies on these
topics over the last several decades, from measurement
of indoor air concentrations to simulating concentrations from gas appliance use, both in California and in other regions .25,26,54–60 Studies measuring pollutant emissions or indoor air concentrations have consistently found that the use of gas appliances can result in concentrations of pollutants — particularly NO2 — at concentrations above the level of ambient (outdoor) air quality standards .
Specifically, studies of California residential buildings have examined the association between gas appliances
and measured indoor levels of air pollutants, including CO, NO2, NOX, PM2.5 , UFP, polycyclic aromatic
hydrocarbons (PAHs), and formaldehyde .44–46,48–50,52
While the majority of research focuses on cooking
appliances, such as stoves and ovens, studies have
also measured pollutant emissions or resulting indoor
air pollutant concentrations from the use of heating
appliances, such as furnaces, space heaters, water
heaters, and fireplaces .44,54,56,58,60–63 Furthermore, although many studies have measured PM2.5 and UFP
emissions from cooking with various types of food and
cooking oil, these particulate emissions were often
attributed to the food and cooking method rather than
the operation of gas appliances .55,57,64
Several studies have found gas stove usage results
in both peak and weekly average NO2 concentrations
exceeding the level set by both the chronic California
Ambient Air Quality Standards (CAAQS) ambient an-
nual average limit of 57 micrograms per cubic meter
(µg /m3), and the acute National Ambient Air Quality
Standards (NAAQS, set by the US EPA) 1-hour limit of
188 µg /m3 or 100 parts per billion (ppb) . Please refer to Section 2 .2 .2 for relevant considerations regarding the use of outdoor air quality standards to assess exposure to indoor air quality .27,45,46,49,52 Studies of California res- idential buildings have reported NO2 levels in excess of these standards in kitchens and bedrooms, suggesting
elevated concentrations throughout the entirety of the
home during a single instance of gas cooking, especially in homes using gas stoves with pilot lights, or without venting range hoods .49,50,52 Research from earlier decades on unvented gas space heaters measured NO2 and PM2.5
concentrations above standards, but these types of heat- ing devices are no longer legally sold in California .58,60,65,66 Research has found that CO is a lesser potential health concern than NO2 if appliances are operating properly .
Gas stoves have been associated with increased levels
of indoor CO in California homes, but these increases in concentrations are generally negligible,27,49,51,52 with only a small portion of homes exhibiting CO concentrations
above the CAAQS 1-hour standard of 23 milligrams per
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 13 cubic meter (mg/m3) .45,46 However, CO concentrations above the CAAQS 8-hour standard of 10 mg/m3 have
been reported during preparation of a full meal and under broiling conditions, without range hood use (though
these were peak values and these concentrations did
not persist for an entire 8-hour period) .27 Furthermore, CO emissions may rise to higher concentrations under
conditions where appliance ventilation mechanisms
fail or are not used, or the stove is misused for heating residences, and we address the former in Section 2 .1 .2 .
CARB reports that CO is responsible for 13 to 36 deaths from non-fire-related CO poisoning in California each
year since 2000 .67
As mentioned at the beginning of Section 2, although we do not include PM or formaldehyde in our quantitative
assessment, it is important not to overlook these
pollutants when considering the effect of gas appliances on air quality . Similarly to CO, studies measuring PM2.5 emissions found that increases attributed solely to gas kitchen appliances (with no cooking of food involved,
though sometimes a pot of water was heated) were
negligible .49,52 One caveat mentioned previously is that cooking can be a significant source of exposure to PM2.5 due to heating and combustion of food and cooking
oil, resulting in indoor concentrations far in excess
of the NAAQS 24-hour threshold of 35 µg/m3 .27,55,57
Furthermore, studies have measured substantial peak
UFP concentrations during gas stove cooking, both with
and without food .28,30,44,48,57,68,69 All studies including tests of gas stoves used without food demonstrated
elevated UFP concentrations .28,44,68 Emissions from
episodic sources such as cooking, with either gas
or electric stoves, constitute a majority of indoor
UFP concentrations .30,48,68,70–72 UFP concentrations
during episodes of cooking without a range hood are
comparable to those found outdoors on high pollution
days .28 Since no government standards for UFP
concentrations currently exist, and the health effects
of UFPs are not yet fully characterized, it is challenging to regulate these smaller particles . Though we do not
quantitatively evaluate UFP in this report, we discuss the health effects of UFP exposure in Section 2 .2 .4 . Studies have also estimated particle emissions from other types of gas appliances, such as water heaters and home
heating devices, but most assess particle emissions in
the units of particle number (PN, which better reflects UFP levels) and not PM2.5 . Based on CARB’s annual
projections of county-level, estimated total emissions for PM2.5 from residential gas combustion, and as seen for
other pollutants as well, water heaters and home heating appliances have significantly higher overall emissions
than gas cooking appliances . However, water heaters and home heating appliances are vented outdoors (outside
the building envelope), as mandated by regulations .73
Gas appliances also emit formaldehyde,27,4 4,62 but
some studies did not find a statistically significant
association between gas appliance use and indoor
formaldehyde concentrations .45,46,74 A CARB analysis
reported formaldehyde concentrations far above the
acute Reference Exposure Level (REL) of 55 µg/m3
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 14 set by the California Office of Environmental Health Hazard Assessment (OEHHA) during gas cooking,
both with and without food .27 An REL is the maximum
concentration at which not to expect any adverse, non-
cancer health effects at each given exposure duration
(acute, 8-hour, or chronic) . However, an LBNL study of California homes found that although 95% of homes
tested had formaldehyde concentrations above the
OEHHA chronic REL, these levels were not statistically
significantly associated with gas appliances .45 In
addition, gas appliances emit acetaldehyde,27,4 4 a highly toxic and carcinogenic VOC similar to formaldehyde,
with recent research indicating low levels emitted from gas stove burners .44 Due to the lack of emission data
and statistically significant evidence reported in the
primary literature, we did not include formaldehyde or
acetaldehyde in our quantitative analysis .
Besides experimental research, several simulation stud- ies have modeled gas appliance emissions and reported
exposures to indoor pollutants, including CO, NO2, and
formaldehyde .47,53,59 Simulation studies specific to Cal- ifornia residential buildings found that gas stove emis- sions comprise up to a third of total weekly average con- centrations of indoor CO and NO2, and even conservative estimates of indoor CO and NO2 concentrations may
frequently be in excess of the 1-hour and 8-hour CAAQS
standards for CO and the 1-hour NAAQS standard for
NO2 . 47,53 One study estimated that in a typical winter week, 12 million and 1 .7 million Californians may be ex- posed to NO2 and CO levels (respectively) in exceedance of acute, ambient air quality standards .47 Furthermore, the study estimated that formaldehyde emissions from
gas cooking appliances alone would lead to exposures
exceeding the OEHHA acute RELs (for approximately
50% of homes) and chronic RELs (for less than 10% of
homes), depending on the season .47
2.1.2. FACTORS INFLUENCING EMISSIONS TO THE
INDOOR ENVIRONMENT
Apart from the frequency of appliance use, as well as
trends toward reduced heating (and increased cooling)
demand for California buildings, there are several
important factors influencing the quantity of emissions to indoor residences .
Appliance ventilation conditions
The effective removal of combustion products generated
by gas appliances is a core element of health and safety in buildings . Home heating devices and water heaters
must have their exhausted gases moved through the
appliance, out of the venting apparatus, and into the
outdoors .75 The National Fire Protection Association 54:
National Fuel Gas Code provides safety requirements
for the ventilation of gas appliances and requires that gas space heaters and water heaters be vented to the
outdoors, while the California Health and Safety Code
prohibits the sale of unvented gas space heaters, and
mandates the existence of ventilation equipment above
stoves and ovens .76,77 Even with such legislation in place, unvented or inadequately vented gas cooking appliances
are present in some California homes .78,79
One significant concern regarding appliance ventilation failure is pollutant backdraft and resulting spillage, which put residents at greater risk of CO poisoning . Backdraft refers to the backward movement of exhausted gases
through the venting system, and spillage refers to the
resulting leakage of exhausted gases from the appliance into the indoor environment, which leads to the buildup of pollutants inside the home .80 Although the frequency of backdrafting and spillage events is not well-established, this has led to excessive CO exposure, which has severe consequences: The Centers for Disease Control and Pre-
vention (CDC) estimated 393 deaths in the United States from unintentional, non-fire-related CO poisoning asso- ciated with consumer products in 2015 .81 In California specifically, the Tracking California program (previously known as the California Environmental Health Tracking
Program) estimated 643 emergency department visits
due to non-fire-related CO poisoning in 2016 .82
One main cause of backdraft and spillage is
depressurization, which happens when air removed
from the house by weather-related forces, open doors
and windows, or mechanical appliances such as exhaust
fans and furnaces, results in a lower air pressure
indoors as compared to the outdoor environment .80,83
Depressurization interferes with the mechanisms of
combustion appliances, resulting in backdrafting and
spillage . Depressurization is usually periodic rather
than continuous,83 although research has observed
instances of continuous depressurization .84 A literature review conducted by LBNL found that while up to 50%
of appliances tested were at risk of backdrafting, few
instances of “sustained” backdrafting or spillage were
recorded .80 There are several challenges associated with monitoring for backdrafting and spillage in homes .80
Due to the existing limitations, questions regarding the frequency, duration, and severity of backdrafting and
spillage events remain to be answered .
Low-income and elderly residents may face increased
risk of CO poisoning from gas combustion appliances .
A 2016 LBNL report on wall furnaces in apartments
did find that backdrafting can occur frequently in small residences when kitchen and bathroom exhaust fans are
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 15 on a high setting, though this study had a relatively small sample size (16 apartments) and highlighted the need
for additional research .85 Nonetheless, this points to the potential for added risk for residents, including elderly populations, who live in smaller rental apartments, are often low-income, and face existing challenges with the burdens of appliance maintenance .86,87
Considering the uncertainty surrounding improper
ventilation, one of our two sensitivity analyses (See
Section 2 .2 .2 and Appendix A .1 .2 for details) involved a scenario to account for the potential of indoor
emissions from appliances, such as water heaters and
home heating devices, that are designed to solely emit
combustion pollutants outdoors . Of course, the location of the appliances, which can vary from wall furnaces in living rooms to water heaters in designated mechanical
closets, are not aspects we were able to control for, but are important considerations for future research .
Appliance maintenance considerations
Maintenance issues can have a pronounced impact on
the emissions produced by combustion appliances, as
well as on ventilation efficiency . Old appliances that have not been maintained are at risk of ventilation failure, resulting in potentially dangerous levels of pollutants being emitted into the indoor environment .44,61,80 Other problems requiring maintenance include heat exchanger
failures and blocked flues in furnaces .
Appliance tuning, which refers to various aspects of
appliance maintenance, can also have a substantial
impact on emissions . Well-tuned appliances often emit
substantially less CO than poorly tuned appliances,
sometimes differing by an order of magnitude .80,83,88–91 However, there are only limited studies on appliance
maintenance and safety mechanisms, and these topics
warrant further research .
2.1.3. FACTORS INFLUENCING COMBUSTION
POLLUTANT CONCENTRATIONS IN AN INDOOR
ENVIRONMENT
There are several factors that significantly affect the indoor air pollutant concentrations resulting from
combustion .
Range hoods and capture efficiency
Gas stoves often lack adequate exhaust ventilation . The low-rise residential building ventilation code ASHRAE
62 .2 requires the installation of range hoods in kitchens, with minimum airflow and maximum noise levels, but it
is estimated that only half of new homes in the United
States comply with this standard .78 Furthermore,
a study of California homes, using data from a real
estate website, approximated that 47% of homes had
combination microwave/range hoods, which do not meet
the airflow and noise level requirements of ASHRAE
62 .2, while 7% of homes had no range hoods at all .79 A 2014 LBNL report highlighted a specific need for the
development of over-the-range microwaves that meet
the ASHRAE 62 .2 requirements .92 The body of research
on the use and effectiveness of range hoods is growing .
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 16 Research on kitchen range hoods has demonstrated
their potential to reduce exposure to pollutants emitted by combustion appliances, as well as evaluated noise
levels, since sound is one reason why people often elect not to use range hoods .45,52,57,68,92–97 Range hoods differ considerably in their ability to remove pollutants from the indoor environment and can be assessed using
capture efficiency as a measure of overall effectiveness .
Capture efficiency refers to the proportion of pollutants emitted from an appliance that are removed by the range hood before they enter the indoor environment .52,93
The capture efficiency of range hoods is often above
50%, though it varies widely depending on the cooktop
burner used (typically lower for front burners), as well as coverage and quality of the hood .52,57,68,93,95 In one study of California residences, the use of range hoods resulted in significant reductions in air pollutant concentrations within the home .52
While studies have shown that range hoods can
significantly reduce exposure, they are infrequently
used and not always available or appropriately sized or installed .78,79,92 Small-scale survey results show that less than 35% of California residents use range hoods
when cooking,98 while a CARB study of California homes
found that 54% of participants did not use their range
hood .96 As mentioned previously, studies have shown
that the excessive noise produced by many range
hoods and fans is a primary reason for the lack of range hood use .92,96,97 It is important to note that increased awareness of the need for ventilation during cooking and encouragement of range hood use may reduce exposures
to pollutants emitted by combustion appliances for those with properly sized, installed, and maintained hoods .
However, renters sometimes do not have range hoods
installed, or existing hoods are not vented outdoors and may not meet standards, therefore putting renters at
heightened vulnerability to exposure to air pollutants
from gas cooking appliances .99 Due to the infrequency
of range hood use, our analysis assumed that there is
no significant range hood use as a health-protective
conservative assessment, though it is still useful to
consider our estimates in the context of conditions
involving range hoods as well, with varying levels of
capture efficiency .
Residence size and ventilation
The size and ventilation of an indoor space are primary determinants of indoor air quality . In smaller residences, indoor air pollutants are distributed across a smaller
space and thus, are more concentrated .100–102 The
volume of an indoor space is also a major factor in the determination of AER, which is expressed as the number
of indoor air volumes replaced with outdoor air per hour .102 Ventilation (and AER) significantly influence indoor air quality . Inadequate ventilation has been associated
with higher concentrations of indoor air pollutants,
including NO2, PM2.5 , and VOCs, as well as adverse
health outcomes .103–106 In fact, a recent study of
commercial buildings in California determined that such buildings rarely meet ventilation standards .107 There
are reported challenges associated with meeting
ventilation standards in multifamily housing as well .108 A dilemma that has emerged in recent years, particularly
with climate change considerations, is the dichotomy
between promoting energy efficiency and improving
indoor air quality . The tightening of building envelopes — essentially, residential air-sealing — has the potential to save billions in energy bills and reduce infiltration of outdoor air pollutants,109 but it also decreases ventilation, degrading indoor air quality .110 More energy-efficient buildings with tightened envelopes have, in some cases, been associated with adverse health outcomes due
to worsened indoor air quality,111,112 though a recent study on green buildings found several health benefits
for individuals who moved from conventional housing
to green-renovated housing .106 Due to the crucial
role of ventilation in determining indoor air quality,
developments in building energy efficiency should be
balanced with the preservation of indoor air quality .
2.1.4. WHY THIS ISSUE MATTERS: INDOOR AIR
QUALITY, HUMAN HEALTH, AND ENVIRONMENTAL
JUSTICE
As mentioned in the introduction, considering that
people in the U .S . spend almost 90% of their time
indoors, indoor air quality and human health are closely linked .21 Many studies have assessed the health impacts of various indoor air pollutants .30,113,114 We discuss each primary combustion pollutant (CO, NO2/NOX), as well as
the pollutants we do not quantitatively evaluate (PM and formaldehyde) and their associated relationships with
human health in detail in Section 2 .2 .4 .
In the context of household gas appliances, the
potential transition from gas to all-electric home
appliances could benefit low-income households and
environmental justice communities by improving both
indoor and outdoor air quality . These communities face disproportionate air-pollution burdens115 and limited
access to clean energy resources .
While many issues related to gas appliance use and
vulnerable populations are challenging to quantify
without primary data collection, we aim to aggregate
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 17 as much of the relevant quantitative and qualitative information as possible on this topic as it connects
to environmental justice and equity . A few key equity
considerations related to gas appliance use, which
we explore further in Sections 2 .2 .2 and 2 .2 .3, are as follows:
• SUPPLEMENTAL USE OF COOKING APPLIANCES FOR
HEATING RESIDENCES. Though the frequency is not
well-established, some research indicates that low-
income and minority residents may disproportionately
use kitchen appliances for the purpose of heating
their residences (instead of using designated heating
devices) .
• HOUSING CHARACTERISTICS: TENURE, QUALITY,
RESIDENCE SIZE, AND APPLIANCE MAINTENANCE.
Residences occupied by low-income populations
are often older, and use older, less efficient, and
unmaintained appliances . These older appliances may
not be regularly maintained due to the cost required
and a lack of available funds to repair them, or lack of landlord attention .37–39 Low-income residences are
also likely to be smaller in size and have inadequate
ventilation, resulting in higher indoor pollutant
concentrations .40,41
• TIME-ACTIVITY PATTERNS. Time-activity patterns, or
the amounts of time spent performing various activities throughout the day, substantially affect exposure to
pollutants in various environments . Notably, children
in low-income families may spend a greater amount of
time at home and indoors than other populations .
• CUMULATIVE EFFECTS: HEALTH AND ENVIRONMENTAL
JUSTICE IN CALIFORNIA. Residents in environmental
justice or “disadvantaged” communities [defined by
SB 535 as the top 25% scoring tracts in OEHHA’s
CalEnviroScreen tool, used for assessing environmental
justice vulnerability] face some of the worst air quality in the state . Gas appliance emissions add to the
persistent outdoor air pollution and can compound
existing environmental burdens, placing low-income
residents and people of color at even greater risk of
adverse health effects from air pollution .
2.1.5. KNOWLEDGE GAP AND CONTRIBUTIONS TO
THE LITERATURE
Based on the literature review, there is a clear need
to: (1) aggregate information on related studies of gas appliances, indoor air quality, equity, and health; and (2) conduct data analysis to provide additional clarity on
these issues through quantitative estimations .
While there is clear evidence of a relationship between indoor air quality and health, and combustion falls
under that domain, there is some inconclusive literature related to gas appliance use and specific health effects .
The broader relationship between NO2 and adverse
health effects is well-established,116 but a recurrent
theme in the literature is the uncertainty regarding
the link between indoor NO2 exposures from gas
combustion and respiratory illness .30,31,113,117 Challenges to the clarification of this relationship include the
variabilities between appliances, use activity patterns, and home size and ventilation .118 Studies have also
highlighted the uncertainty regarding the relationship
between residential indoor concentrations and personal
exposure .119 While several studies investigating gas
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 18 appliances and asthma exacerbation produced mixed
results, evidence supports a clearer association between gas appliances and asthma and respiratory symptoms
in children,33,120,121 with one meta-analysis reporting that children living in homes using gas for cooking have a 42% higher risk of having asthma .33 While we did not estimate the association between specific health symptoms and
use of gas appliances, our literature review and analysis aim to clarify the relationship between pollutants
associated with gas appliance use and human health .
As described earlier, there are a limited number of recent studies that simulate and measure indoor air pollutant
concentrations resulting from the use of gas appliances, and many are focused entirely on gas stovetop ranges .
We used similar methods and data as some of those
studies to conduct our analysis, but we included multiple types of appliances and conducted a detailed literature review on the use of gas appliances, related pollutants, and human health .
We modeled pollutant emissions, concentrations, and
exposures resulting from gas appliance use in different housing types in California and linked these exposures
to potential health effects via comparison to state and national standards . To our knowledge, there are no
existing literature review and secondary analysis studies that tie together indoor air quality modeling for various pollutants, housing types, and low-income vulnerability in California .
2.2. RESULTS AND DISCUSSION
2.2.1. EMISSION FACTOR DATABASE
Results of statistical analyses
To model the effects of gas appliances on indoor air
quality, we first created an emission factors (EF)
database for residential gas appliances (see Appendix
A, Section A .1 .1 for details) . Our regression models, designed to predict EFs in units of ng/J (nanogram/
Joule), found that there are significant differences in EFs among gas appliance types .
Unsurprisingly, the EFs of gas appliances have declined over time, likely due to the technological advances of
appliances and pollutant capture technology, which
reduce emissions . Consistently, as the year of the
publication from which EFs were gathered became
more recent, the ng/J emissions decreased (e .g ., a
paper in 1995 would report higher emissions than a
paper published in 2009, with a statistically significant difference); this indicates that emissions have reduced over time . For NOX, there is a statistically significant increase in EFs for appliances designed to be vented
outdoors (e .g ., water heaters and home heating devices) .
EF and emission rate estimations
As described in Appendix A, the EFs of gas appliances
in a unit such as ng/J do not reflect the amount of
pollutants released during the consumption without
accounting for the mass burning rate (MBR, in J per time period) of different gas appliances . The emission rate in µg/hour (µg/h), or the amount of pollutants released in a specific time period during the usage of different gas appliances, is the product of the EF in ng/J and the MBR in J/h, since both factors affect the rate that combustion byproducts are released into the air .
EFs in ng/J, and emission rates in µg/h (the amount of
pollutants released in a specific time period during the usage of different gas appliances) for each appliance
category and pollutant were calculated as described in
Appendix A .
Table 2-1: Mean emission factors (EF) and emission rates (ER) for each appliance type .
Appliance Type CO (mean) NO2 (mean) NOX (mean)
EF (ng/J) ER (µg/h) EF (ng/J) ER (µg/h) EF (ng/J) ER (µg/h) Gas Stove 52 670,000 10 130,000 38 440,000
Gas Ovenii 92 1,700,000 8.3 150,000 36 640,000
Gas Water Heateriii 18 3,200,000 3.4 490,000 25 2,300,000 Gas Heater 16 1,300,000 5.3 320,000 37 1,600,000
Note: Values correspond to total emission factors and rates when the appliance is turned on, regardless of whether an appliance is vented outdoors (meaning not all these emissions travel indoors).
ii. Separate EFs were calculated for stoves and ovens, but throughout this report we combined the two for most analyses (using a sum of emission rates), due to the nature of existing data (e.g. the RASS and CARB State Implementation Plan data). More specifics available upon request. iii. This analysis incorporates both tankless and storage water heaters, which do have significantly different emissions for CO; tankless water heaters have higher emissions of CO. We did not control for these differences in our analysis. These higher emissions also occur for formaldehyde, which we did not quantitatively assess in this report. 44
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 19 Descriptive statistics from the results of our EF
calculations are listed in Table 2-1 . Kitchen appliances have higher EFs in ng/J for all pollutants, as compared with other gas appliances, but energy usage for water
heaters and home heating devices is much higher
(see Figure B-2 in Appendix B), which is why resulting
emissions are higher for water heaters and home heating devices .3,15,42,44,45 This is consistent with previous studies that have observed higher emissions from water heaters
and home heating devices . Residential water heating
results in the highest level of emissions of each of these pollutants .
2.2.2. INDOOR AIR QUALITY IMPACTS AND
SUSCEPTIBILITY
Indoor air quality model results
As described in Appendix A, a mass-balance model 122
was used to estimate indoor air concentrations of
CO, NO2, and NOX under various scenarios of kitchen
appliance use, including peak concentrations in the
kitchen and time-weighted concentrations throughout
the entire home (considering that cooking only occurs
for a small portion of the day) . This is described
further in Appendix A (Section A .1 .2), but the model
produced an output with the highest concentration
value, representing the emissions while cooking; we
averaged these to establish the peak concentration
levels presented in Table 2-2 . For peak concentration
levels, we used kitchen-specific volumes, and for values weighted by appliance usage time, we used entire
residence volumes, under the assumption that pollutants would mix into the residential space over time . We are conservatively assuming there is no range hood use, and that all kitchen appliances are unvented .
iv. An underlying assumption is that concentrations and exposures are directly proportional.
Table 2-2 provides an overview of the average
concentrations calculated using the model . We used a
range of 15 minutes of cooking to 2 hours of cooking to represent a spectrum of potential cooking patterns .
Defining exceedances of air quality thresholds
Throughout this section, we used California (CAAQS)
and U .S . EPA (NAAQS) ambient (outdoor) air
quality standards as a metric for health effects from
exposure .iv These standards are the maximum allowable
concentration of a pollutant present in outdoor air
that will not have a known, adverse impact on human
health and are developed to apply to long-term, ambient outdoor air quality, averaged over time periods . It is not possible to actually exceed these outdoor standards in an indoor environment due to the technical definition .
Therefore, we apply target thresholds using the
standards as a guide to provide context for indoor air
quality . We refer to three different types of thresholds based on the standards: 1) acute (1-hour for NO2 and
CO), 2) 8-hour (for CO), and 3) chronic (annual mean
for NO2 — there is no annual mean standard for CO) .
When we use the term “acute,” we are referring to 1-hour standards . For CO, we refer to 8-hour standards directly as such . For NO2, when we use the term “chronic,” we are referring to the annual mean standards .
When an exceedance is referenced in this report, it
means that the modeled indoor air concentration is
higher than the threshold levels based on the standards in Table B-7 . When we refer to the percentage of
exceedances, we are discussing the percent of our
modeled indoor air quality estimates that exceed
thresholds (please see Appendix A for additional details) .
We evaluate the indoor air quality exceedances of the
Table 2-2 : Average indoor air concentrations by appliance – peak (highest concentration) vs . time-averaged 15-minute cooking, 1-hour cooking, and 2-hour cooking scenarios .
Appliances Pollutant Average Peak
Concentration
(µg/m3)
Average Time-weighted
Concentration
(µg/m3)
Average Time-weighted
Concentration
(µg/m3)
Average Time-weighted
Concentration
(µg/m3)
Duration Peak 15-minute cooking 1-hour cooking 2-hour cooking Location Kitchen Entire Residence Entire Residence Entire Residence Stoves and ovens CO 18,000 (16 ppm) 950 (0.83 ppm) 2,600 (2.3 ppm) 4,900 (4.2 ppm) NO2 1,600 (860 ppb)* 16 (9 ppb) 37 (19 ppb) 64 (34 ppb)* NOX 6,700 (3,600 ppb) 43 (23 ppb) 130 (69 ppb) 250 (130 ppb) Stoves only CO 5,600 (4.9 ppm) 550 (0.48 ppm) 1,000 (0.9 ppm) 1,700 (1.5 ppm) NO2 750 (400 ppb)* 12 (6.4 ppb) 22 (11 ppb) 34 (18 ppb) NOX 2,800 (1,500 ppb) 26 (14 ppb) 62 (33 ppb) 110 (58 ppb) Note: Values marked with * exceed acute CAAQS (for average peak concentration) for CO and NO 2, or 8-hour CAAQS for CO/chronic CAAQS for NO2 (for time-weighted concentrations).
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 20 CAAQS and NAAQS thresholds, overall and for separate residence types, for CO and NO 2 (there are no applicable standards for NOX) .
We compare the peak concentrations (which are direct
model outputs without any time-averaging, reflecting
kitchen concentrations) from our indoor air quality
model to the acute NO2 and CO thresholds, under the
assumption that exceedances of the thresholds for
our estimated peak concentrations only apply under a
scenario where cooking occurs for an extended period
of time and the air quality levels in the kitchen remain elevated for an entire hour (considering the ambient
air quality acute 1-hour threshold described above) .
We compare the modeled 8-hour time-averaged CO
concentrations to the 8-hour CO thresholds, and the 24- hour time-averaged NO2 concentrations to the chronic
NO2 thresholds, under three cooking-time scenarios (15
minutes of cooking, 1 hour of cooking, and 2 hours of
cooking . This is laid out in Table 2-3 .
We focus on the California CAAQS and U .S . NAAQS in
this report, but we also note that Canada has existing
indoor residential air quality guidelines for NO2 that
are more stringent than the U .S . thresholds we discuss throughout the report (i .e ., 170 µg/m3 for 1-hour, and 20 µg/m3 for 24-hour) .123 Thus, the NO2 results we
present here can also be considered through the more
health-protective lens of the Canadian standards . The
Canadian CO standards are similar to the CAAQS and
NAAQS thresholds . All of these standards can be found
in Table B-7 in Appendix B .
Findings: exceedances of air quality thresholds
As shown in Table 2-2, for the use of both stoves
and ovens simultaneously, the 2-hour use of kitchen
appliances results in an average of the time-weighted
NO concentrations of 64 µg/m3, exceeding the chronic (annual mean) NO2 CAAQS threshold of 57 µg/m3 . For 2
hours or less of stove use alone, the average household does not exceed any chronic thresholds .
Exceedances resulting from the use of both kitchen
appliances simultaneously, as well as from stoves
individually, are summarized in Table 2-4, with percent exceedances for both the CAAQS and NAAQS (see
Appendix B, Table B-7 for each threshold level) . As
mentioned previously and in Appendix A, the kitchen
peak concentrations are compared with the acute
thresholds, and the modeled 15-minute, 1-hour, and
2-hour cooking, entire home concentration estimates
have been time-averaged (over 24 hours for NO2 and
8 hours for CO), and are compared with the chronic
threshold for NO2 and 8-hour threshold for CO .
When both stoves and ovens are used simultaneously,
18 .7% of peak CO concentrations inside the kitchen
exceed acute CAAQS, and 11% of 2-hour and 4 .5%
of 1-hour cooking averages throughout the home
exceed 8-hour CAAQS . For CO, less than 1% of 8-hour
concentrations based on a 15-minute cooking scenario
results exceed the 8-hour CAAQS .
Results for NO2 are even more noteworthy, particularly
for peak concentrations . Again, when both stoves and
ovens are used at the same time, more than 90% of
Table 2-3: Concentration and exposure scenarios .
Pollutant Scenario(s) Time-Averaging Location Comparison CO Peak (assuming 1 hour of elevated
concentration for exceedance to apply)
None Kitchen Acute: 1-hour thresholds
NO2 Peak (assuming 1 hour of elevated
concentration for exceedance to apply)
None Kitchen Acute: 1-hour thresholds
CO 15-minutes, 1-hour, and 2-hours of cooking 8-hour Entire residence 8-hour thresholds NO2 15-minutes, 1-hour, and 2-hours of cooking 24-hour Entire residence Chronic: annual mean thresholds Table 2-4 : Percent exceedances of air quality thresholds by appliances used and cooking time intervals .
Appliance Pollutant Acute 8-hour for CO and Chronic for NO 2 % of Peak
Exceeding
CAAQS
%of Peak
Exceeding
NAAQS
% of
15-minute
Use
Exceeding
CAAQS
% of
15-minute
Use
Exceeding
NAAQS
% of
1-hour Use
Exceeding
CAAQS
% of
1-hour Use
Exceeding
NAAQS
% of
2-hour Use
Exceeding
CAAQS
% of
2-hour Use
Exceeding
NAAQS
Stoves and
ovens
CO 19% 11% 0.4% 0.4% 4.5% 4.5% 11% 11%
NO2 93% 99% 2.0% 0.1% 15% 2.5% 45% 15%
Stoves
only
CO 4.4% 2.6% 0.1% 0.1% 1.0% 1.0% 2.7% 2.7%
NO2 61% 81% 1.7% 0.4% 5.0% 1.1% 15% 4.1%
Note: In the peak scenarios, when comparing concentrations to air quality thresholds and acute exposures, we assume cooking time occurred for the entire 1-hour period that the acute threshold applies.
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 21 peak NO2 concentrations inside the kitchen exceed
acute CAAQS . Additionally, 45% of 2-hour and 15% of
1-hour cooking averages throughout the home exceed
chronic CAAQS, though only 2% of 15-minute cooking
concentrations exceed chronic CAAQS .
When stoves are used independently, and resulting
emissions and concentrations are lower, CO exceedances
are again much less significant, while for NO2,
exceedances of acute NAAQS occur up to 80% of
the time for peak concentrations, and exceedances
of chronic CAAQS occur up to 15% of the time for the
longest cooking time (2 hours), both based on the most
stringent thresholds .
Keeping in mind the air quality thresholds, these
percentages represent the frequency that air quality
can no longer be considered safe (i .e ., having no known, adverse impact on human health) .
Figure 2-1 and Tables 2-5 and 2-6 provide housing-
type-specific assessments . Figure 2-1 depicts average peak concentrations inside kitchens for each housing
type, along with acute, ambient air quality standards
for CO and NO2 . Variations in peak concentrations
shown in Figure 2-1 are a result of variations in residence volume and associated ventilation rates . Our findings
for apartments, townhouses, and single-family homes
(SFHs) in Tables 2-5 and 2-6 are a disaggregation of the data in Table 2-4 and serve to inform the public about
the variations in indoor air concentrations by building type . It must be noted that these findings are based on averages of housing volume and ventilation found in the literature, and may not represent all homes; therefore, these should only be used as general indicators . While Table 2-2 and Table 2-4 include a 15-minute cooking
scenario, we did not include this particular scenario in the housing-specific tables (2-5 and 2-6) for simplicity .
If the 15-minute cooking scenario is of further interest, Tables 2-2 and 2-4 can be used to extrapolate the data .
To appropriately interpret these tables and figures, we refer to housing estimates in California . Throughout
the state, approximately 58% of residences are SFHs,
30% are apartments, and 9% are attached homes, such
as townhouses .2 The remainder (~3%) are primarily
mobile homes, but because those make up such a
small percentage of the California housing stock, we
Figure 2-1: Peak concentrations in the kitchen resulting from usage of stoves and ovens simultaneously, by pollutant [(a) CO and (b) NO2 ] and housing type .
Indoor Peak Kitchen Concentrations ( µg /m 3 )
CO
Apartment
100
1,000
10,000
100,000
1,000,000
Townhouse SFH
(a)
Indoor Peak Kitchen Concentrations ( µg /m 3 )
NO 2
Apartment
100
1,000
10,000
100,000
1,000,000
Townhouse SFH
(b)National Ambient Air Quality Standards
California Ambient Air Quality Standards
Table 2-5: Average peak (kitchen) and time-weighted, 8-hour average (entire home) CO concentrations from use of gas kitchen appliances in various residence types, and percentage of scenarios in which concentrations exceed air quality thresholds .
Residence
Type
Acute - Peak 8-hour
Peak Conc. in
Kitchen ( µg/m3)
% of Cases Above
1-hour Standards
8-hour Conc. 1-hour
Cooking Entire Home
(µg/m3)
% of Cases Above
8-hour CAAQS
1-hour Cooking
8-hour Conc.
2-hour Cooking
Entire Home
(µg/m3)
% of Cases Above
8-hour CAAQS
2-hour Cooking
Apartment 28,000 27.6% 3,900 8.2% 7,400 18.2%
Townhouse 13,000 12.8% 2,000 2.5% 3,500 6.9%
SFH 12,000 12.2% 1,800 1.8% 3,300 5.8%
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 22 do not include them in this analysis . However, this is an important area for additional study . There are existing challenges with the provision of utilities in mobile
home parks; the California Public Utilities Commission
approved a Mobile Home Park Utility Upgrade Program in
2014, which is still operating .124
These concentrations and exceedances are comparable
to the findings in previous studies, both modeled and
measured, many of which are discussed in Section 2 .1 .1 .
One notable finding is that exceedances are all higher for apartments, primarily due to smaller residence sizes .
A 2012 analysis conducted by LBNL measured
pollutant levels in 155 California homes and found
that approximately 10% of residences studied had
chronic (6-day, in the case of this study — typical
passive monitoring methods only capture multiday NO2
averages) indoor air concentrations of NO2 exceeding
chronic CAAQS, which are comparable to our 1-hour
cooking results of 15% exceedances for stoves and ovens used simultaneously, and 5% for just stove use (Table
2-4) .45 They had a low number of exceedances for CO,
which aligns with our findings (Tables 2-4 and 2-5) that CO exceedances are much less frequent than NO2 . A
modeling analysis of Southern California homes found a
similar pattern between CO and NO2 exposures .53
We did find a high percentage of peak exceedances of
acute (1-hour) thresholds for NO2 when both stoves
and ovens are used (Table 2-4 and 2-6), and associated
exposures apply, assuming the household cooked for
the entire hour, but this is not necessarily a typical
exposure scenario; it depends on cooking habits in the
home . When only stoves are used (Table 2-4), the risk
assessment more closely matches existing literature on
emissions from stovetop ranges . A simulation-based
study of California residences, which incorporated
seasonality, found that among homes using gas stoves
with no ventilation (the same conditions as our analysis), 55-70% exceeded NAAQS NO2 standards .47 Though we
found that almost all of our estimated concentrations
exceeded the 1-hour NO2 NAAQS threshold for
concurrent stove and oven use, we found 80%
exceedances when solely stoves are used (Table 2-4),
which is comparable .
Overall, our analysis echoes the assertions of many
existing studies that exceedances of regulatory
standards for NO2 may be frequent and are a cause for
concern . Additional information on the pollutant levels measured and simulated in the literature is provided in Section 2 .1 .1 .
Sensitivity analysis: using kitchen appliances for
heating residential spaces and the impact of improper
ventilation
In situations where designated heating devices are
insufficient in a residence, kitchen appliances are
sometimes used as heating devices . Additionally, as
discussed in Section 2 .1 .2, ventilation technology does not always work exactly as designed . Due to the lack
of existing data sources, we were unable to quantify
the frequency of occurrences of the use of kitchen
appliances for heating residential spaces, or the
frequency of improper ventilation that results in pollutant spillage to the indoor environment . We have provided
a brief analysis of existing knowledge to cover the
spectrum of this potential issue .
Again, while it is challenging to quantify the frequency of these types of occurrences, there are many
circumstances under which backdrafting and spillage
of combustion pollutants can occur, and evidence
suggests this may happen in homes across the United
States (see Section 2 .1 .2) . Under these various scenarios where appliances designed to be vented outdoors are
improperly vented and combustion gases spill into the
interior, peak exposures rise significantly, particularly because when used, these types of appliances have
higher hourly emissions than kitchen appliances (see
Table 2-1) . One key assumption for this portion of
the analysis is that the pollutant spillage is occurring for the entire time the appliance is operating . Due
to the conservative nature of this assumption, we
included several capture efficiency scenarios; we have
provided this range of scenarios to account for various percentages of combustion pollutants traveling indoors
Table 2- 6: Average peak (kitchen) and time-weighted 24-hour average (entire home) NO 2 concentrations from use of gas kitchen appliances in various residence types, and percentage of scenarios in which concentrations exceed air quality thresholds .
Residence
Type
Acute - Peak Chronic
Peak Conc. in
Kitchen ( µg/m3)
% of Cases
Above Acute
Standards
Time-weighted Conc.
1-hour Cooking Entire
Home (µg/m3)
% of Cases Above
Chronic CAAQS
1-hour Cooking
Time-weighted
Conc. 2-hour
Cooking Entire
Home (µg/m3)
% of Cases Above
Chronic CAAQS
2-hour Cooking
Apartment 2,400 98.3% 46 27.2% 85 65.8%
Townhouse 1,100 90.8% 31 8.4% 52 31.9%
SFH 1,100 87.0% 33 12.5% 56 33.9%
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 23 instead of out through ventilation . These concentrations are for each appliance used individually, as opposed to concurrently .
Compared to the average peak concentrations presented
in Tables 2-2, 2-5, and 2-6, the concentrations resulting from improper ventilation presented in Table 2-7 are
elevated in several cases . For water heaters, these
concentrations commonly exceed the acute CAAQS
threshold for CO (two out of four capture efficiency
scenarios) and NO2 (all four scenarios) . For NO2,
concentrations for home heating device use also exceed
the acute CAAQS threshold for all but the highest capture efficiency scenario . These represent peak concentrations throughout the entire home, not just the kitchen (since there is not a specific, designated room for these other appliances); therefore, these are modeled on a larger
volume than peak concentrations in the other tables .
It is important to note that if the appliance of concern is in a small room, concentrations in that room will be significantly higher than what is recorded in Table 2-7 .
There is limited information on the supplemental use
of cooking appliances (stoves and ovens) for heating
residences (meaning appliances not designed for
heating are used to heat spaces in the home) . When
gas cooking appliances are used for heating, there are
two particularly important considerations: the greatly
increased duration of use, compared to when they are
used for cooking, and that they constitute an unvented
heating source . These factors elevate indoor combustion pollutant levels . A study investigating the relationship between respiratory illness in children, gas stove use, and ventilation found that in homes where adults used
the stoves for both cooking and heating, as opposed to
solely for cooking, children had significantly higher odds of being diagnosed with asthma and experiencing other
respiratory symptoms .35
Under a scenario where kitchen appliances are used
for supplemental heating for approximately 4 hours,
time-weighted exposures in the entire home rise by a
factor of 4 .8 for NO2 as compared to 1 hour of cooking, and the chronic CAAQS threshold is exceeded in 90%
of instances . The 8-hour CO concentrations would
rise by 2 .8 times in this scenario . If only the stove is used for both cooking and supplemental heating, time-
weighted exposures for NO2 rise by a factor of 4 .0 and exceed the CAAQS threshold 51% of the time when
supplemental heating occurs . On average, the 8-hour CO concentrations would rise by 2 times when compared to
1 hour of cooking .
Though frequency of use for these purposes is not well
established, particularly in recent literature and datasets, there are reasons for equity-related concern . A report based on the National Health and Nutrition Examination
Survey (NHANES) III (1988-1994) found that use of a
gas stove or oven for heating was highest among adults
in the Southern U .S ., with lower-income households
engaging in such use of combustion appliances
approximately twice as often as higher-income
households .125 In recent years, the U .S . Census Bureau’s American Community Survey (ACS) started collecting
data on supplemental heating devices, but found no clear income- or race-based trends . In each income group,
2 .6-5 .4% of households reported using cooking stoves
for supplemental heating . Significantly fewer households use gas ovens with the oven door open for heating, as
opposed to cooking stoves .
There have been a few articles written on the use of gas stoves for supplemental heating, though several date
to the early 1980s . This behavior has been identified
as a contributor to elevated indoor NO2 levels in low-
income housing — particularly in combination with poor
ventilation and small apartment size30 — and the use of gas stoves for heating is linked with childhood asthma .118 In the previously mentioned NHANES III of more than
8,000 children, those who lived in homes where a gas
stove or oven was used for heat were more likely to have Table 2-7: Mean peak CO and NO 2 exposures in the entire home associated with pollutant backdrafting/spillage and various capture efficiencies .
Appliance Pollutant Concentration with 0%
Capture Efficiency
(µg/m3)
Concentration with 25%
Capture Efficiency
(µg/m3)
Concentration with 50%
Capture Efficiency
(µg/m3)
Concentration with 75%
Capture Efficiency
(µg/m3)
Heating devices
CO 11,000 8,200 5,600 3,000
NO2 730* 550* 370* 190
NOX 3,900 2,900 2,000 990
Water heaters
CO 31,000* 24,000* 16,000 8,100
NO2 1,400* 1,100* 710* 360*
NOX 6,400 4,800 3,200 1,600
Note: Values marked with * exceed acute CAAQS for CO and NO 2.
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 24 clinically diagnosed asthma .118,121 In a 1980s study of 700,000 residents in New York City, approximately 50%
of those with gas stoves, but no gas heating appliances, were found to use gas stoves for supplemental heating .126 A study of patients with symptoms of CO exposure
found that use of gas stoves for heating was a significant predictor of high carboxyhemoglobin levels, indicating
CO poisoning .127 In a sample of residences in the United Kingdom, use of gas ovens for heating was significantly related to NO2 concentrations in both kitchens and
bedrooms .128 However, in a study of low-income public
housing in Boston, supplemental heating with stoves was not a significant predictor of indoor NO2 concentrations, though gas stove heating behavior was only assessed
via an initial survey and not during the environmental
sampling period .129 Researchers have called for further research and education on the impact of supplemental
heating with gas stoves, and have identified the
improvement of heating technology as a means of
limiting the use of gas stoves for heating .
2.2.3. ADDITIONAL EXPOSURE AND
VULNERABILITY CONSIDERATIONS
This section includes a brief, qualitative discussion of other factors associated with exposure and associated
risk .
Synergistic effects of multiple air pollutants
There is potential for synergistic effects of exposure to multiple pollutants, including our pollutants of interest — CO, NO2, and NOX — meaning that exposure to multiple
pollutants at one time may not be a direct sum of the
individual health impact of exposure to each pollutant .130 The health effects of pollutants such as PM2.5 , NOX/
NO2, and CO are evaluated separately in our report
and others, but these exposures occur simultaneously,
and concurrently with other pollutants not included in
our analysis, such as heavy metals, PAHs, and VOCs
(both during cooking, and due to other sources of indoor exposures) .27,119 We are not able to account for this in our analysis, but it is an important consideration .
Body weight, inhalation rates, and gender
Body weight and inhalation rates play a major role in
determining the effects of personal exposure to airborne contaminants . Higher inhalation rates result in greater exposures, and lower body weights increase the effects
of exposure, due to a higher dose per unit of body weight .
Body weight and inhalation rate are also correlated,
and thus, the two factors should be considered in
v. We do not expand upon it in this report, but it is important to note that the gender disparities in cooking frequency as well as associated exposures for children are international issues, particularly in countries where traditional cookstoves are used to burn solid fuels, leading to significant environmental health concerns. 135,136
conjunction .131 Inhalation rates increase with body weight, with substantial increases found when comparing
people of normal weight and people who are overweight;
additionally, males have slightly higher inhalation rates than females .
Body weight and inhalation rate considerations are most important in regard to children, who are particularly
susceptible to the adverse health effects of air pollution .
Children perform a substantially higher level of daily
physical activity than adults, which culminates in a
far greater intake of air into the lungs .132 Furthermore, children breathe 50% more air per unit of body weight
than adults, due to having a greater lung surface area to body weight ratio .133
We did not incorporate body weight and inhalation rates into our quantitative assessment, but the California
Department of Toxic Substances Control (DTSC)
releases and regularly updates a set of Human Health
Risk Assessment (HHRA) notes134 focused on different
aspects of risk assessment, and HHRA Note 1 is entirely focused on default exposure factors, including body
weight and inhalation rate . Additionally, the 2011 US EPA Exposure Factors Handbook offers a comprehensive
overview of inhalation rates for children and adults
according to age, gender, body weight, and activity
level .131 According to this handbook, domestic tasks such as cooking are considered light intensity activities .
In terms of gender, the variations between men and
women related to body weight and inhalation rate apply, but in regard to gas appliances, there is an additional consideration regarding which gender spends more time
cooking and thus, is in closer proximity to gas appliances being used in the kitchen . Surveys have indicated that women do spend more time preparing meals than menv,
resulting in additional exposure to combustion pollutants in households with gas appliances .137,138 A 1991 CARB
study of children’s activity patterns also found the
prevalence of potential exposure to fumes from a gas-
powered oven to be consistently elevated for children of all ages and genders .139
Housing characteristics: tenure, quality, residence size, and appliance maintenance
Disadvantaged populations disproportionately
experience poor housing conditions that can be
detrimental to health .140 A recent State of the Nation’s Housing report from Harvard University found that
more than half of the nation’s low-income population
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 25 live in high-poverty neighborhoods .141 Housing
quality related to safety is substandard in many low-
income residences,142,143 and is inextricably linked
with public health concerns; also, appliance age and
maintenance fall under this umbrella of housing safety
considerations .40,144 Lower-income families are often renters: The median income for renters in California is $50,000 annually, while the median income for home
owners is $90,070 annually .2 Lower-income families
often do not have control over, or incentive to engage in, appliance replacement and maintenance; additionally,
these families have less disposable income to spend
on resolving maintenance issues . We can refer to the
sensitivity analyses in 2 .2 .2, which highlight a potential health concern associated with old and unmaintained
appliances: improper ventilation resulting in spillage
of combustion pollutants into the living space . Lack of maintenance may result in improper ventilation occurring for extended periods of time . Thus, there is a need for future research on the sociodemographic trends in
households with appliance maintenance and ventilation
concerns .
Housing size variations are accounted for within the
indoor air quality model; a smaller home with the
same ventilation rate as a larger home will have higher concentrations of pollutants due to having lower
volume . Our findings from Section 2 .2 .2 demonstrate
that exceedances for CO and NO2 are all higher for
apartments, primarily due to smaller residence sizes .
Additionally, individuals in the kitchen and other rooms will be in closer proximity to gas-burning devices .
This may have air quality and health implications
for low-income populations living in smaller homes .
Furthermore, low-income residences are more likely to
be overcrowded,145 which may affect cooking frequency . “Overcrowding” is defined as occurring when there is
more than one person living in a residence as there are rooms in the residence (including rooms such as the
living room and kitchen) . According to the California
Department of Housing and Community Development,
California’s overcrowding rate is 8 .4%, which is more
than double the U .S . average of 3 .4% .145
Time-activity patterns
Research has shown that children in low-income families spend more time in the home,146 and are thus exposed
to indoor air quality issues in the home more often than children from families with a higher socioeconomic sta- tus . Limited literature indicates that this may be particu- larly due to lower participation in after-school programs, resulting in greater exposure to indoor air pollutants in the home .147,148 This is an area for future study .
Cumulative impacts: health and environmental justice
in California
As we briefly touched upon in the background section,
low-income and environmental justice communities
are often disproportionately affected by adverse
environmental conditions, and historically, have less
access to clean water and air, as well as to clean energy
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 26 resources . Many environmental issues in disadvantaged communities are externalities that these communities
do not have control over, and these issues contribute to health disparities .
Existing research has explored the cumulative effects
faced by vulnerable communities, finding that there
are many complex, nuanced relationships between
environmental and social factors that can result in
significant (and potentially nonlinear) health effects
on the population .115,149 This includes the exacerbation of the effects of harmful environmental exposures —
such as air or water pollution — and the enhancement
of psychosocial stress experienced in impoverished
neighborhoods . There are also potential synergistic
effects from exposure to multiple pollutants, and
multiple stressors, that need to be explored further to be fully understood .115,149
Research suggests that regulatory interventions must
consider different elements of cumulative effects to
reduce environmental inequities and associated health
disparities .115 It is critical to note that any air quality impact from the use of gas appliances compounds upon
preexisting, complex, and adverse environmental and
health burdens in these communities .
2.2.4. HEALTH EFFECTS OF AIR POLLUTION
In this section, we present the existing evidence
surrounding each pollutant’s relationship with gas
appliance use, and describe the specific acute and
chronic health impacts associated with exposure . We
address indoor exposures specifically, but this section is also generally applicable to outdoor, ambient exposures to these pollutants . Table 2-8 summarizes the health
effects described in this section .
2.2.4.1. Nitrogen oxides
NOX, predominantly consisting of NO and NO2, are
widespread gaseous pollutants . NO2 is primarily formed from the oxidation of NO .155 Existing research evaluates the human health impacts of both NOX and NO2, but
much of recent literature focuses on NO2, particularly
since a growing body of evidence indicates that it leads to premature mortality . Therefore, we focus specifically on NO2 in this section . The 2016 US EPA Integrated Science Assessment (ISA) on the health effects of NOX found
the literature to be suggestive of a causal relationship between chronic NO2 exposure and respiratory effects,
cardiovascular effects, cancer, and mortality, though it did not make an absolute determination .116
As mentioned in Section 2 .1 .1, combustion appliances — specifically, gas cooking appliances — have been found
to increase indoor NO2 levels above acute CAAQS and
NAAQS thresholds .119 Studies have observed higher NO2
exposures in homes with gas stoves compared to those
with electric stoves .27,22 1 When cooking with gas, peak concentrations of NO2 in the kitchen can reach levels
far in excess of the CAAQS 1-hour NO2 threshold .34
Individuals who cook with gas can be exposed to high
levels of NO2 due to close proximity to the stove . These peak concentrations of NO2 are comparable to those
reported in Section 2 .2 .2 .
Though exposure to NO2 has been linked to adverse
health outcomes, there is some mixed evidence regarding the association between indoor NO2 exposure from
combustion appliances and specific respiratory health
impacts .31,33 Studies from the last several decades
have found a robust association between NO2 from
gas cooking and increased risk of respiratory illness
Table 2-8: Overview of health effects of main studied pollutants .
Pollutant Health Effects
Acute Chronic
Nitrogen oxides
(NOX)
Decreased lung function, asthma exacerbation,
respiratory infection, 118,120,150–153 stroke 154
Premature mortality, 155–158 lung and breast cancer, 156,159 cough, shortness of breath, asthma, wheezing, respiratory illness in children 33,33,91,117,120,160–163
Carbon monoxide
(CO)
Death, brain damage, seizures, memory loss, dementia,
headaches, dizziness, nausea 164–168
Brain and heart toxicity, 164,169–173
heart failure and cardiovascular disease, 167,174–176
low birth weight 177
Fine particulate matter
(PM2.5)
Stroke, increased blood pressure 154,178–180 Premature mortality, 22,181 bronchitis, asthma onset and exacerbation, 185–189
low birth weight and preterm birth 190–194
Ultrafine particles
(UFP)
Increased blood pressure 179,195 Cardiovascular disease, 196,197 neurological disorders 198,199
Formaldehyde Respiratory/eye/skin irritation, sneezing, coughing, nasal congestion, 103,200,201
drowsiness, chest tightness, shortness of breath, 103,200,202 asthma exacerbation, 203,204
death (higher doses) 205
Cancer,103,172,206–210
asthma and bronchitis in children, 200,211,212
damage to respiratory system, 205,211,213–219
headaches, sleep disorders, memory loss, 202,205
birth defects, low birth weight, spontaneous abortion
205,213,218,220
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 27 in children, such as asthma, wheezing, and other
respiratory symptoms .33,91,120,162,163 NO2 exposure from gas appliances is implicated in many other respiratory
symptoms, including cough, lung obstruction, and
shortness of breath .33,117,160,161 Women may be at
higher health risk from NO2 exposure, due to greater
susceptibility and higher frequency of cooking compared to men .117,138,160 Research suggests that due to the
widespread use of gas for cooking, NO2 exposure from
gas appliances has a substantial public health impact,
particularly in children, as described in Section 2 .2 .3 .33 The respiratory effects of acute NO2 exposure more
broadly include decreased lung function, asthma
exacerbation, and increased risk of respiratory
infection .118,120 Children are at the highest risk of health effects from NO2 exposure .118,120,222 Short-term NO2 exposures above the CAAQS 1-hour standard
are associated with lung inflammation, particularly
in individuals with asthma or chronic obstructive
pulmonary disease (COPD) .150–153 Acute NO2 exposure is also associated with increased risk of hospital admission and mortality from stroke .154
Chronic NO2 exposure is suspected to be a driver
of air-pollution-related mortality and is associated
with premature death .156,222 Studies have observed a
relationship between chronic NO2 exposure and all-
cause, cardiovascular, respiratory, and lung cancer
mortalities, with greater risks among populations with
preexisting diseases .155–158 Chronic NO2 exposure also increases the risk of lung and breast cancers,156,159 and evidence also suggests impact to pregnancy outcomes,
such as low birth weight .223–225 A substantial body
of evidence supports an independent effect of NO 2
on mortality, and epidemiological research on this
burgeoning topic is accumulating quickly .155–158 Because NO2 is ubiquitous and large populations are exposed,
even small increases in NO2 may have extensive public
health consequences .155–158,222
2.2.4.2. Carbon monoxide
Although exposure to dangerous levels of CO is
preventable, many instances of CO poisoning still occur in homes,226 resulting in estimated expenses of $1 .3
billion annually in the United States .227,228 As mentioned previously, the Tracking California program estimated
643 emergency department visits due to non-fire-
related CO poisoning in 2016,82 and CARB estimates
there have been 13-36 non-fire-related CO poisoning
deaths in California annually since 2000 .67 Although CO emissions from gas appliances can be negligible,27,49,51,52 and most of the CO concentrations presented in our
results in Section 2 .2 .2 are below the state and national 8-hour standards of 10,000 µg/m3, dangerously high
CO exposures from gas appliances may occur due to
mechanical and ventilation failures .164,229 Excessive CO exposures, often associated with gas appliances,
have been found to cause severe damage to brain
tissue,164–168 and can result in long-term or permanent neurological symptoms such as seizures, memory loss,
and dementia .228–232
CO exposure has diverse, acute human health effects,
with symptoms ranging from headaches, dizziness, and
nausea at low concentrations, to neurological damage
and death at high concentrations .165,168 CO is an insidious pollutant; because it is tasteless, odorless, and induces nonspecific symptoms, CO exposures often remain
undetected by both victims and medical professionals .233 While the health effects of acute exposure are well-
established, the long-term impact is not as well-studied or understood . Chronic exposure to low concentrations
of CO was found to be associated with adverse health
effects on multiple organ systems, with substantial
evidence demonstrating toxic effects on the brain
and heart .164,169–173 The World Health Organization
(WHO) suggests potential toxic effects of chronic CO
concentrations above 6 .9 mg/m3 .172 Increases of 11 .5 mg/ m3 in ambient CO levels are associated with increased
risk of hospital admission for congestive heart failure, particularly in the elderly,167,174,175 whereas increases of slightly more than 1 mg/m3 in 1-hour maximum CO
concentrations are associated with increased risk of
cardiovascular-disease-related hospitalizations .176
In addition, children are especially vulnerable to CO
exposure due to their developing nervous systems
and high metabolic rates,229 and exposure to ambient
CO levels close to those of the WHO threshold
listed previously in this report is associated with an
increased risk of low birth weight .177 There are other risks associated with CO exposure during pregnancy as
well .234
2.2.4.3. Particulate matter
PM is a leading cause of worldwide mortality and
morbidity, and there is evidence that PM2.5 pollution
adversely affects cardiovascular and respiratory health through a myriad of pathways .22,181 Recent research,
based on the Global Burden of Disease project, found
that PM2.5 led to approximately 8 .9 million deaths in
2015, which is higher than previous estimates .24 PM
concentrations are often higher indoors than outdoors
and come from a variety of sources, including cooking,
household aerosol products, office equipment, and
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 28 transportation of outdoor pollution into the indoor
environment .182
Cooking with combustion appliances can be a significant source of PM2.5 and UFP exposure,26,27,64,235 though
studies of PM2.5 exposure from these types of appliances have shown a decrease over the last several decades,
likely due to technological advances resulting in reduced emissions . Although both gas and electric stoves
generate particle emissions, gas stoves have been found to produce greater particle exposures .26,28 Cooking
methods, and the type of food being cooked, can also
have a substantial impact on PM2.5 emissions, and the
use of cooking oils with higher smoke temperatures
has been identified as a means of reducing PM2.5
emissions .236 As mentioned previously, many of
these experimental tests involved food, and the PM2.5
concentrations observed cannot solely be attributed to
the appliances . Additionally, as mentioned in Section 2 .1, PM emissions from gas water heaters and home heating
devices are significantly higher than PM emissions from kitchen appliances .
Short-term exposure to PM2.5 is associated with
cardiovascular and cerebrovascular disease, including
strokes and increases in blood pressure .154,178–180 An increased risk of hospital admissions and mortality
for stroke has been observed per 10 µg/m3 short-term
increase in ambient PM2.5 .154
PM2.5 also has well-established, chronic health effects .182 An extensive body of evidence supports a significant
association between PM2.5 and all-cause mortality .22
PM2.5 exposure is associated with an increased risk of
cardiovascular and respiratory mortality, with a greater increase in risk than seen for NO2 .156–158 The impact
of PM2.5 pollution also includes increased emergency
room visits and general hospital admissions,182–184 and chronic PM2.5 exposure is linked to certain cardiovascular diseases and chronic respiratory conditions as well, such as bronchitis and asthma onset and exacerbation .185–189 Chronic PM2.5 exposure is particularly harmful to
pregnant women and children . Long-term PM2.5 exposure
during pregnancy is associated with increased risk
of low birth weight and preterm birth per 10 µg/m3
increase in PM2.5 .190–194 A study of more than 600,000 births in California over a 7-year period revealed a
significant association between PM2.5 exposure and low
birth weight .237 One recent study found that the dose- response relationship between preterm birth and PM2.5 is linear at lower pollution levels, suggesting increased risk even at low concentrations .190
Evidence indicates that combustion processes produce
large amounts of UFPs .48,57,236 UFPs can also be formed by nucleation, where low volatile gas phase species are converted to aerosol phases . Nucleation events can
be provoked by the operation of gas appliances, where
combustion processes produce gaseous emissions such
as CO and NO2 .44,238,239 In an LBNL study of combustion appliance emissions, the vast majority of particles
emitted by gas stoves were found to be in the ultrafine range,44 and a study of residences in Northern California found cooking to be the greatest source of indoor UFPs .48 A chamber study demonstrated substantial UFP number
concentrations of more than 300,000 particles/cm3
emitted by both gas and electric stoves,240 while a
residential study of gas stoves in Taiwan recorded PM2.5 concentrations of up to 100 µg/m3 and UFP emissions of
up to 1,400,000 particles/cm3 .241
Burgeoning research indicates that UFPs significantly
affect human health, though regulatory intervention
to control emissions of these particles is particularly challenging, due to their small size .198 Emerging evidence posits UFPs are potentially more toxic and harmful than PM2.5 on a per unit mass basis .179,242
Chronic exposure to UFPs is associated with increases
in markers related to cardiovascular disease risk .196,197 Both ambient UFP concentrations and UFP emissions
from indoor sources have been found to increase
blood pressure in adults and children .179,195 UFP
exposure also has pronounced respiratory effects: A
study of five European cities over a 10-year period
found an association between UFP and respiratory
hospitalizations during warm periods, with the
strongest effects seen among children 0-14 years old .243 Researchers suggest that UFPs may contribute to
neurological disorders as well .198,199
Exposure to PM has well-established acute and chronic
health effects, and though we were not able to quantify indoor residential exposures to PM2.5 and UFPs in this
report, due to limited available data, PM exposure due to indoor gas appliance operation should be considered in
future air pollution and health effect studies .
2.2.4.4. Formaldehyde
Formaldehyde is a part of a larger family of VOCs,
which are common indoor pollutants with sources
including building materials, carpeting, paint, furniture, personal care products, and combustion .30,244,245
Newer residential buildings have been found to
produce greater formaldehyde and VOC emissions
than older buildings .200,244 Additionally, recent evidence
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 29 suggests that infiltration of outdoor formaldehyde
contributes substantially to indoor concentrations .246,247 Formaldehyde is an extremely prevalent pollutant,
and a study of California homes found that 95% had
formaldehyde levels above the OEHHA chronic REL .45
Formaldehyde has been formally established as a human
carcinogen by regulatory agencies such as the WHO and
the International Agency for Research on Cancer (IARC), and noted potentially carcinogenic by other agencies,
with evidence of it causing nasopharyngeal cancer and,
to a lesser extent, leukemia .103,172,206–210 Apart from its carcinogenic effects, formaldehyde is a sensory and
respiratory irritant with both acute and chronic non-
cancer health effects .103,200,201 However, formaldehyde exposures often occur in conjunction with large numbers of other VOCs and indoor air pollutants; thus, identifying the direct health effects of formaldehyde has proven
challenging .200,213,248
Formaldehyde can be formed as a byproduct
of combustion processes, due to incomplete
combustion .103,247 Although most existing literature
focuses on formaldehyde emissions as a result of
cigarette smoking, wood combustion, and off-gassing
from building materials, a number of studies have
investigated the effects of formaldehyde formation
due to gas appliances and residential cooking
activities .27,4 4–46,74 Although the operation of gas
appliances has been found to result in formaldehyde
emissions, the concentrations measured in such studies
were often below the OEHHA chronic REL of 9 µg/
m3 .27,4 4 Additionally, several studies did not indicate any significant contribution of gas appliance use to indoor formaldehyde concentrations .45,46,74 These results are consistent with research showing that building materials are the primary sources of indoor formaldehyde
emissions .30,244,245 Preliminary evidence in mice suggests intermittent exposures to higher concentrations of
formaldehyde are more damaging than constant low-
level exposures, as the dose-response relationship
between formaldehyde and its impact on human health is
not linear .214 This may be of importance when considering formaldehyde emissions from gas appliances, as these
exposures are acute and unpredictable, as opposed
to chronic and stable (as in the case of formaldehyde
emitted from building materials) .
Respiratory irritation is the most common, acute effect of formaldehyde exposure, along with related symptoms
such as dry skin, sneezing, coughing, eye irritation,
and nasal congestion .200,202,205,207,211,249 Formaldehyde exposure is also associated with a range of nonspecific symptoms, including drowsiness, chest tightness, and
shortness of breath .103,200,202 Relatively low formaldehyde concentrations are associated with increased risk
of asthma and chronic bronchitis in children .200,211,212 Formaldehyde also increases sensitivity to allergens in asthmatics, even at the WHO-recommended maximum,
30-minute average concentration .203,204 Acute
formaldehyde poisoning at higher doses is associated
with severe symptoms, including fever, vomiting,
abdominal pain, and in extreme circumstances, death .205 Chronic formaldehyde exposure is an issue of concern
as well, as effects have been found to increase over time .
In addition to increasing cancer risk, chronic exposure to formaldehyde results in a multitude of symptoms,
including reduced lung function, tremors, and damage
to the nasal passages .205,211,213–219 The relationship between chronic formaldehyde exposure and poor
respiratory health may be particularly important for
children .250 Additionally, chronic formaldehyde exposure has neurotoxic effects, causing symptoms such as
headaches, sleep disorders, and memory loss .202,205
Formaldehyde is also a reproductive and developmental
toxicant associated with birth defects, low birth weights, and spontaneous abortion .205,213,218,220
While exposure to formaldehyde can result in life-
threatening, adverse health conditions, it remains unclear whether formaldehyde is a significant concern related
to gas appliance use . Since formaldehyde is a known
carcinogen, this topic demands further research .
2.2.5. ASSUMPTIONS AND LIMITATIONS
Due to the limited scope of this project, we did not
conduct any primary data collection; we only analyzed
existing literature and datasets . While we used as many relevant data sources as we could access, data paucity
was a major limitation for this report . Particularly for conducting future quantitative analyses with regard to
equity, the development of additional, publicly available databases to include more detailed and higher spatial
resolution data would be a significant asset .
There are other factors associated with exposure that
we were unable to control for, including the location
of appliances throughout the home (water heaters
and home heating devices), and seasonality (which
affects ventilation, as well as the ambient pollutant
concentrations used in the indoor air model) .29,47 There were also challenges associated with determining a
standard residence volume and ventilation rate for each residence type, so these values are based on estimates
from primary literature, and public data and reports .
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 30 Details on our calculations of volumes and ventilation rates are included in Appendix A . We also did not
assess any exposures or other dangers associated with
electrification, as we focus on combustion pollutants in this report .
There are also limitations associated with the use of
an indoor air quality model . This model assumes the
pollutant of interest reaches a steady state, which
is more appropriate for emissions occurring over
a consistent period, not for analyzing short-term
emissions . Our analyses also operated under various
assumptions about the time spent using kitchen
appliances . We approximated applicable time periods,
but we also wanted to provide varying assessments
considering different amounts of time using the
appliances, so that readers of this report can gain
a better understanding of the implications of their
own appliance-use habits . Additionally, as mentioned
previously, the 1-hour (acute) thresholds compared to
our peak kitchen pollutant concentrations only apply
to exposures under a scenario where air quality levels
remain elevated for an entire hour .
Finally, there are indoor air quality issues associated with the use of gas cooking appliances that will remain despite the implementation of electrification, and
we do not account for this . Some PM emissions are
associated with cooking oils and foods, and there are
no mitigation methods for this, other than the use of
ventilation devices such as range hoods . We do not claim that the transition to electric appliances would make a substantial difference in terms of emissions from cooking oils and food .
This report does not compare the benefits and costs
of electrification versus improving range hood use and
efficiency in terms of reducing indoor air pollution . This is an important consideration that needs to be included in any full-scale assessment of indoor air pollution
mitigation techniques . We touched briefly upon range
hoods in Section 2 .1 .3 .
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 31 3 OUTDOOR AIR QUALITY AND HEALTH
EFFECTS
Section 2 discussed the indoor air quality issues and resulting health effects associated with the use of residential gas appliances. This portion of the report covers an equally relevant realm: how the use of these appliances affects outdoor (ambient) air quality, the extent to which residential building electrification would reduce ambient exposures to the pollutants of concern, and the resulting premature mortality and morbidity reductions throughout the state. Section 3.1 provides background information from a literature review, and Section 3.2 contains the results and discussion. The objectives of this section are to:
• quantify the total emissions of CO, NO2, and NOX due to gas appliances across California;
• model changes in ambient PM2.5 due to reduced emissions of NOX and PM2.5 from a hypothetical, residential building electrification scenario; and • estimate the potential reduction in mortality associated with the modeled scenario.
In the results and discussion portion of this outdoor
air quality section of the report, as described in these objectives, we included various quantitative assessments of four pollutants: CO, NO2, NOX, and PM2.5 . In Section 3 .2 .1, we assessed the total emissions of CO, NO2,
and NOX based on our EFs calculated in Section 2 .
In Sections 3 .2 .2 and 3 .2 .3, we considered only two pollutants: NOX and PM2.5 . We first estimated reductions in secondary PM2.5 levels due to a calculated reduction in NOX and resulting nitrate PM2.5 . We then incorporated CARB data on PM2.5 emissions from residential gas
appliances to estimate the total reduction in PM2.5 from the replacement of gas appliances, representing changes in primary and secondary (nitrate) PM2.5 from gas use .
We then assessed health impacts from reductions in
those estimated ambient PM2.5 levels . This is described in detail in Appendix A .
3.1. BACKGROUND
In this literature review section, we discuss the following relevant topics:
• current electrification research as it relates to criteria air pollutants, and related policy and implications of
electrification more generally (3 .1 .1);
• the relationship between gas appliances and outdoor air quality (3 .1 .2);
• resulting outdoor air quality, health, and environmental justice implications (3 .1 .3); and
• the identified knowledge gap we aim to fill (3 .1 .4) .
3.1.1. CALIFORNIA’S ELECTRICITY LANDSCAPE
Electricity and criteria air pollutant emissions
Residential building electrification has multiple
potential co-benefits, spanning the domains of air
quality, health, and climate change mitigation .251,252 Reducing air pollutant emissions through electrification
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 32 would improve air quality and promote public health
while also limiting production of GHGs . The coupling
of electrification with decarbonizing electricity
generation represents an ideal scenario, producing
these associated co-benefits . Of course, even without
complete, wide-scale decarbonization of electricity
generation, decreasing the carbon-generating proportion of the power mix will be conducive to climate change
mitigation .253
There are several existing research studies on air quality and health co-benefits from electrification .254–256
A recent modeling study predicted that achieving the
California Executive Order S-3-05 target of reducing
GHG emissions to 80% below 1990 levels by 2050
through a focus on electrification would result in signif- icant public health benefits .256 A comprehensive decar- bonization approach, prioritizing electrification and clean, renewable energy sources, with 85% electrification in
commercial and residential sectors, would reduce 2050
emissions of NOX by 34% and PM2.5 by 33% .256 Further-
more, the pollutant reductions would result in the avoid- ance of an estimated 12,100 premature deaths annually
by 2050, due to changes in ambient ozone and PM2.5 ,
with a monetized estimated value of $109 billion .256 This particular scenario, focused on the implementation of
clean, renewable energy and high levels of electrification, had significantly more health co-benefits than a scenario focused on combustible, “renewable” fuels . Similarly, a study modeling the air quality impact of Assembly Bill
(AB) 32257 (The Global Warming Solutions Act of 2006,
which facilitated the enactment of the Cap-and-Trade
Program), predicted cumulative emissions reductions of
approximately 15% for NOX and 1% for PM2.5 throughout
California .254 Air quality improvements due to AB 32
were predicted to avoid approximately 880 premature
deaths per year by 2030, with an estimated monetized
value of $5 .4 billion .254 Another California-focused study on reaching the 2050 GHG emissions targets predicted
air-pollution-associated premature mortality reductions of up to 2,760 deaths per year by 2050, with an estimat- ed monetized value of up to $20 billion annually .255
A 2018 CEC report investigating future decarbonization
scenarios reported high levels of building electrification to be an effective, relatively low-risk, and low-cost GHG mitigation strategy as compared to other mitigation
measures, and a key factor in reducing gas consumption .7 On a related project in 2019 for the CEC, the E3 group
and the Advanced Power & Energy Program at University
of California, Irvine (UCI) evaluated the air quality and health effects of electrification; they evaluated multiple scenarios to reduce GHG emissions from 1990 levels
by 80% by the year 2050, including a high building-
electrification scenario, and a no building-electrification scenario .258 Similar to the CEC report, they also found that building electrification has the potential to be
low risk and low cost, in this case compared to the
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 33 widespread use of renewable gas .258 One portion of
this project involved using the U .S . EPA’s Benefits
Mapping and Analysis tool (BenMAP) to conduct a
health-impact analysis for a high building-electrification scenario . Building electrification was projected to result in lower PM2.5 concentrations, particularly in winter,
and the BenMAP analysis reported health savings of
approximately $200 million over 10-day episodes in
summer and winter, due to mitigation of ozone and
PM2.5 from the high building-electrification scenario .258 Reductions in secondary PM2.5 formation from lower
NOx emissions from gas appliances were found to have
a major impact on health savings .258 The building-
electrification scenarios modeled by UCI indicate
substantial co-benefits to air quality and human health as a result of reductions in NOx, PM2.5, and ozone . However, these scenarios were designed to reduce GHG emissions
rather than target criteria pollutant reductions .258
EPRI prepared a 2019 report, commissioned by the CEC,
investigating the air quality implications of electrification in California across multiple sectors .15 It estimated that electrification would result in substantial reductions of PM2.5 and ozone across California, with monetized health benefits estimated to be $108 billion per year in 2050 .15 It also found that electrification of residential and
commercial stationary sources resulted in the majority
of PM2.5 reductions (61%), with significant impacts from the reduction of residential wood combustion .15
One aspect to keep in mind throughout this analysis,
which will be mentioned again in the Results and
Discussion section, is that electricity generation at gas power plants emits both GHGs and criteria air pollutants .
Even if all residential gas appliances were transitioned to electric appliances, the electricity required to power these appliances must still be generated by some form
of fuel, and gas power plants currently produce almost
half of the electricity generation in the state . Therefore, in order to avoid increased emissions from gas power
plants, building electrification must be based on the
preface that the electric power system will continue
to decarbonize and shift to clean energy . As California increasingly builds and relies upon zero-carbon
electricity sources such as wind and solar energy, which is state-mandated by the 100% Clean Energy Act of
2018, or SB 100, the overall GHG and air quality benefits of electrification will increase (This law enacted the
Renewables Portfolio Standard (RPS), which mandates
that 100% of electricity sold must be generated
from zero-carbon energy sources by 2045 259 . This is
discussed further in Section 3 .2 .2 .
Overall, GHG emissions reductions and in particular,
electrification, offer immense co-benefits with regard to air quality, health, and economic value, with the largest benefits predicted in densely populated, metropolitan
areas .7,15,254–256
Building electrification in California: policy and
economic implications
California is a national leader in clean energy and climate policy . Though local emissions of criteria pollutants
are a byproduct of combustion processes (the focus
of this report), there is a substantial body of research on the relationships between energy sources and
climate change mitigation,3,42,251,260–262 and climate change mitigation continues to be a main driver of
policy that affects electrification status throughout
the state . Together, SB 32 (which extends AB 32), SB
100, California’s B-55-18 Executive Order to achieve
carbon neutrality by 2045, and other forthcoming bills
provide a strong legislative framework for mitigating
climate change, with aggressive targets for reducing
GHG emissions .257,263 Research has identified wide-scale electrification of multiple energy-consumption sectors, including residential buildings, as an important requisite for achieving California’s GHG emissions goals; 4,7,8 this transition will require policy support .264
Unlike the national landscape, where approximately
25% of all homes in the United States are all-electric,265 roughly 90% of California’s homes consume gas for
various fueling purposes . The majority of California
homes use gas for heating and cooking: Recent AHS
surveys estimated that 64% of California homes used
gas as their primary heating fuel, and that 67% of homes used gas as their primary cooking fuel .2 One example
of a scenario with high rates of building electrification, as described in the recent report by E3, finds that more than 7 million existing California residences will need to be retrofitted with electric technologies .4 A different report posed another scenario showing that if gas were
entirely phased out at an accelerated pace, there would be more than 13 million residential buildings in California retrofitted by 2045 .266
In July 2019, Berkeley became the first city in California to introduce legislation to phase out the use of gas piping in new buildings, with limited exceptions .267 Since then, roughly 30 cities and counties have adopted ordinances
supporting or requiring the construction of all-electric buildings .268
A study modeling the impact of future building
electrification found that all-electric homes performed better than mixed-fuel buildings, in terms of both GHG
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 34 emissions reductions and abatement costs associated
with the construction of buildings compliant with the
Title 24 California Building Standards .269 In particular, the electrification of space and water heating appliances presents an opportunity for substantial GHG emissions
reductions, which aligns with our results from Section 2 regarding criteria pollutant emissions .260,270,271
Additionally, a recent study investigating the
consequences of residential building electrification in California predicted several load-distribution effects
to the electrical grid .4 Building electrification would result in more efficient utilization of the power grid as characterized by an improved load factor, which is the
ratio of average- to peak- electricity demand . The report forecasted changes in seasonal electricity demand, with higher overall winter electricity loads and slightly lower peak summer electricity loads .
Transitioning to electric heat pumps would provide
effective heating and cooling in buildings, and the recent maturation of heat pump technologies has been identified as an efficient and beneficial component of future
electrification .4,272,273 This is all particularly relevant as California temperatures are rising . Projected increases in the intensity, frequency, and duration of heat waves274 could result in higher air conditioning adoption, increased cooling demands, and decreased heating demands .
There are several economic considerations related to a
transition from gas to electricity . Fugitive CH4 emissions produced when gas appliances are not operating (e .g ., emissions from pipe leaks) are estimated to incur an
economic cost to consumers of approximately $30
million annually .3 Research has also found that building all-electric reduces construction costs considerably,
and lowers energy bills overall .275 One research group projected consumer energy bill savings for a range of
appliances, and found that despite higher capital costs in certain scenarios, the majority of households will have both bill and life-cycle savings as a result of building electrification .4 However, one consideration identified by a recent report is that as demand for gas falls, cost for gas customers increases significantly .258 In a wide-scale electrification scenario, this may result in low-income gas consumers requiring rate protection or financial
assistance for transition . This report also predicted higher utility bills for mixed-fuel homes than for all-electric homes after year 2030 .258 This may have multifaceted
effects that constitute equity concerns; higher utility bills for gas-using homes will further encourage
electrification, but low-income consumers who rent
their homes and do not own their gas appliances, or are unable to afford purchasing electric appliances, may bear a disproportionate burden of transition costs . One report addressed other barriers to residential electrification throughout the state, highlighting that, despite the fact that all-electric homes have lower maintenance costs
(and other considerable benefits, including no direct
emissions), the up-front costs of purchasing high-
efficiency, electric appliances are higher .15 Savings were highest for homes with the greatest heating and cooling demands, such as larger SFHs .
Policy intervention providing incentives for replacing
gas appliances with electric appliances may make the
transition to electrification in California more equitable .
For example, tariffs for all-electric homes offer lower rates for electricity to offset their higher electricity consumption .276 Financing programs providing low- or
no-interest loans for electric appliances could provide a means for making electrification economically feasible, especially in disadvantaged communities .276
3.1.2. RESIDENTIAL GAS APPLIANCES AND
OUTDOOR AIR QUALITY
Relationship between indoor and outdoor air quality
While much of scientific literature focuses on the
transport of outdoor pollutants into indoor environments, emissions from residential gas appliances also transport outdoors, through the ventilation system or through
open windows and other pathways .277 The relationship
between indoor and outdoor air can be characterized by
the indoor/outdoor (I/O) ratio . The I/O ratio is influenced by factors such as natural and mechanical ventilation
and the tightness of the building envelope: Generally,
closed windows lead to low I/O ratios, while well-
ventilated environments have higher I/O ratios .277
Pollutant chemistry
Atmospheric chemistry is important when considering
certain criteria pollutants . NOX is heavily involved in the formation of ground-level ozone .278 Ozone is a secondary pollutant produced by a complex chemical reaction
between NOX, VOCs, and sunlight .278 Ozone is a risk
factor for all-cause, cardiovascular, and respiratory
mortality,279,280 and the global burden of ozone exposure is estimated at almost half a million deaths per year,281 although a recent study estimates that this number could actually be as high as 1 .2 million .282 Contributions to ozone associated with NOX emissions from gas appliance
use are outside the scope of this study .
3.1.3. WHY THIS ISSUE MATTERS: OUTDOOR AIR
QUALITY, HEALTH, BUILDING ELECTRIFICATION,
AND ENVIRONMENTAL JUSTICE
In Section 2, this report discussed indoor air quality
effects from the use of gas appliances in residences;
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 35 however, air pollution from residential gas combustion affects outdoor air quality as well . The relationship
between outdoor air quality and public health is an
important equity issue that merits greater public
awareness and policy development . As introduced in
Section 2 .1 .4, low-income communities and communities of color often have poor air quality and are burdened
with associated negative health effects . More than
40% of all fossil-fuel power plants in California are
disproportionately concentrated near disadvantaged
communities, including in the San Francisco East Bay,
the Sacramento area, Bakersfield, and the Los Angeles
South Bay .283 Furthermore, data from the exposure
mapping tool CalEnviroScreen demonstrate that the
most socially vulnerable communities, such as those
with high poverty, unemployment, and poor health
status, also suffer the highest cumulative burden of
pollution exposure .283,284 These communities often have less access to healthcare and may only seek out medical professionals when in dire need, further exacerbating
the mortality and morbidity effects experienced due to
increased pollutant exposure .15
Apart from these important considerations regarding
outdoor air quality, health, and environmental justice as they relate to gas appliances and electrification, there are numerous other equity considerations related to
the potential transition to electrification . These equity considerations are not a focus of this report but must not be overlooked .
The University of Southern California (USC) Program
for Environmental and Regional Equity (PERE) prepared
a 2019 report for the Climate Equity Network offering
guiding principles for a just and equitable transition to a low-carbon future .283 The report drew attention to the need to protect and prioritize disadvantaged communi-
ties throughout the process of alleviating the effects of climate change . EPRI’s electrification report (discussed previously) also highlights equity considerations .15 EPRI conducted interviews and hosted stakeholder meetings
with environmental justice groups to discuss the results of their electrification analysis, receiving input from the communities affected .15 Beyond simply acknowledg-
ing injustices of the past, both the USC PERE and EPRI
emphasize the need for disadvantaged communities to
play a role in the transition to electrification and renew- able energy, stating that these marginalized populations should be included in the decision-making process as a
means of advancing equity .15,283
A 2019 Greenlining Institute report focused on
equitable building electrification, developing a five-step framework for California to ensure that environmental
and social justice communities are at the forefront
of this transition .285 The steps outlined in this report include working closely with communities to identify
needs and make community-driven decisions, identifying
methods and metrics for data tracking, ensuring
allocation of necessary funding, and successfully
influencing outcomes .285 As mentioned previously,
policy intervention, such as providing incentives for
replacing gas appliances with electric appliances, can
help make the transition to electrification in California more equitable .276 While there are existing low-income
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 36 energy programs throughout the state, Greenlining’s
report identifies that there are significant distributive justice shortcomings in terms of benefit allocation; for several reasons outlined in more detail in their report, program benefits are not maximized for households in
need .285 These reports and many others have highlighted the importance of equity in decision-making regarding
California’s energy future .
3.1.4. KNOWLEDGE GAP AND CONTRIBUTIONS TO
THE LITERATURE
Our study contributes to a growing body of recent
research on the potential impact of expanding
electrification throughout the state . Large-scale
research projects modeling the future of electrification in California have considered the impact across economic
sectors .15,254–256 These studies reported significant reductions in criteria air pollutant emissions, and
associated health and monetary benefits, in addition
to reduced GHG emissions . Our approach is novel in
that it isolates the emissions and health effects of gas appliances in the residential sector, providing estimates of criteria pollutant emissions and their resulting effects on outdoor air quality and health .
Our focus on the emissions associated with residential
gas appliances may serve as a benchmark to be used
by future models of a potential switch to electrification .
This report offers a quantitative approximation of the
contribution of residential gas appliances to overall
air pollutant levels in California . We anticipate that this analysis will contribute to a more developed
understanding of how residential activity impacts air
quality on a larger, statewide scale .
3.2. RESULTS AND DISCUSSION
3.2.1. CONTRIBUTION OF GAS APPLIANCES TO
OUTDOOR AIR POLLUTION IN CALIFORNIA
Total emissions of pollutants from gas appliances
throughout the state
Using our calculated EFs and CEC data on gas
consumption, we estimated total annual emissions
of NOX (which includes NO2) and CO for 2018 (See
Appendix A, Section A .2 .1 for additional details) .
We found that residential gas appliances emitted
approximately 15,900 tons of NOX (with a confidence
interval of 15,500 to 16,300) and 12,000 tons of
CO (with a confidence interval of 10,800 to 13,100)
in 2018 . In comparison, CARB’s annual estimates
for residential gas appliance use were approximately
16,000 tons for NOX and 9,000 tons for CO for 2018 .
There is no specific estimate for NO2 provided by CARB
for comparison here, but we do present NO2 results
separately in Figures 3-1 and 3-2 . Since the numbers are similar in magnitude, indicating consistency between our estimates and CARB’s estimates, we chose to extract
PM2.5 gas combustion emission estimates from CARB,
and use them for the remainder of the outdoor air quality and health analysis in this section to develop more
comprehensive estimates for total pollutant reductions
and mortality impacts . This is discussed in Appendix A in more detail . Figure B-4 in Appendix B depicts total emissions of the three studied pollutants by county from gas appliance use, calculated using the EFs reported in Section 2 .
This report’s findings indicate that emissions from
residential gas appliances account for approximately
3% of total NOX emissions in California (Figure B-5 in
Air Pollutant Emissions in Tons/Year
(a)CO
3,014
4,370
2,830
1,749
Air Pollutant Emissions in Tons/Year
0 2,000
4,000
6,000
OtherStove/
Oven
Water
Heater
Heater
(b)NO 2
993
835
339 269
Air Pollutant Emissions in Tons/Year
0 2,000
4,000
6,000
OtherStove/
Oven
Water
Heater
Heater
(c)NO x6,998
6,222
1,349 1,331
Air Pollutant Emissions in Tons/Year
0 2,000
4,000
6,000
OtherStove/
Oven
Water
Heater
Heater
Figure 3-1: Estimated state-wide emissions of pollutants (a) CO, (b) NO 2, and (c) NOX by gas appliance type .
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 37 Appendix B shows NOX emissions from gas appliances
by county, as compared to NOX emissions from all
sources) .73 Among all counties in California, Los Angeles County has the highest total NOX emissions, as well as
the highest NOX emissions from gas appliances (3,900
tons/year) . As of 2019, 34 million Californians live in counties that are not in compliance with state or federal ambient air quality standards for ozone and/or PM2.5 .286 Considering NOX contributes to ambient PM2.5 , gas
appliances have the potential to add to this pollution
burden .
Comparison of emissions from various types of
appliances
Our analysis indicates that gas water heaters and home
heating devices, such as furnaces, are responsible for
the bulk of outdoor air pollution from gas appliances .
Gas water heaters contribute the most to CO emissions
(36 .5% of all CO emissions come from residential gas
appliances) when compared with other types of gas
appliances, while gas heating appliances emitted the
most NOX (44% of all NOX emissions from residential
gas appliances) in California for 2018 (Figure 3-1) .
This is associated with the relative EFs in ng/J of each pollutant for each appliance type, as well as the percent distribution of use of these appliances, extracted from the Residential Appliance Saturation Study (RASS) .287
This section also shows the estimated apportionment
of emissions for each gas appliance type by air basin, as depicted in Figure 3-2 . Variations by air basin result from different usage profiles for the climate zones designated in the RASS (see Appendix A, Section A .2 .1 for details) .
The two air basins not included in this figure (Great Basin Valleys and Lake County) did not have any available gas consumption data .
Moving forward, this report only discusses NO X, as
ambient CO is not used in the health-impact calculations and NO2 is a component of NOX . As described previously, we assess the contribution of NOX to PM2.5 using
our calculated EFs . We also assess the independent
contribution from PM2.5 emissions from residential fuel combustion to ambient PM2.5 , using data extracted from a CARB database . We did not develop EFs for PM2.5 in
Section 2 due to data paucity .
3.2.2. EMISSION REDUCTION DUE TO RESIDENTIAL
BUILDING ELECTRIFICATION
We simulated an electrification scenario in which 100%
of gas appliances were replaced with clean-energy
electric appliances, under the assumption that all
emissions described in Section 3 .2 .1 are eliminated .
As mentioned in the beginning of Section 3, we first
Heater Water Heater Stove/Oven Other
0 SF Bay Area
San Joaquin Valley
Sacramento Valley
San Diego
South Central Coast
Salton Sea
North Central Coast
North Coast
Mountain Counties
Lake Tahoe
Northeast Plateau
South Coast
Mojave Desert
(a)
1,000 2,000 3,000
CO Emission in Tons/YearAir Basin
Heater Water Heater Stove/Oven Other
0 SF Bay Area
San Joaquin Valley
Sacramento Valley
San Diego
South Central Coast
Salton Sea
North Central Coast
North Coast
Mountain Counties
Lake Tahoe
Northeast Plateau
South Coast
Mojave Desert
(b)
200 400 600
NO 2 Emission in Tons/YearAir Basin
Heater Water Heater Stove/Oven Other
0 SF Bay Area
San Joaquin Valley
Sacramento Valley
San Diego
South Central Coast
Salton Sea
North Central Coast
North Coast
Mountain Counties
Lake Tahoe
Northeast Plateau
South Coast
Mojave Desert
(c)
1,000 2,000 3,000 4,000
NO x Emission in Tons/YearAir Basin
Figure 3-2: Estimated emissions of (a) CO, (b) NO2, and (c) NOX in air basins from gas appliances by type .
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 38 estimated reductions in secondary PM2.5 levels, based on our calculated reduction in NOX (Section 3 .2 .1) and resulting nitrate PM2.5 . We then incorporated CARB data on PM2.5 emissions from residential gas appliances to
estimate the total reduction in PM2.5 from replacement
of gas appliances, representing changes in primary and
secondary (nitrate) PM2.5 from gas appliance use . This scenario is described in detail in Appendix A . Overall, this scenario suggests a reduction in the ambient PM2.5 concentration by an average of 0 .11 μg/m3 per county
(see Appendix A .2 .3 for details) .
Appendix B shows county data for total PM2.5 and NOX
emissions, and the estimated emission reductions with
building electrification per county . Figure 3-3 shows the geographic distribution of emission reductions due to
residential building electrification .
As discussed in Section 3 .1 .1, there are existing emissions from power plants due to electricity generation .73
Gas accounts for approximately half of all electricity
generation in California,288 and thus, if the fuel sources vi. Mortality impact applies to the population aged 30-99; acute bronchitis impact applies to the population aged 8-12; and chronic bronchitis impact applies to the population aged 27-99.
of electricity generation were to remain the same, gas
usage would increase (and associated emissions from
power plants would increase) if the new electric load is not powered by renewable energy resources . However,
utilities are making progress to ramp down electricity
production from gas and deploy clean energy on the grid, in accordance with the state’s zero-carbon requirements .
Additionally, taking into consideration California law SB 100 — which requires all of the state’s electricity to be generated by zero-carbon resources by 2045 — there
will be increasingly less dependence on nonrenewable
resources from power plants, and an increased clean
energy portfolio that contributes to reduced emissions
from power plants .259 Our analysis does not account for any increases in gas used for electricity generation as a means of looking beyond the transition period to zero-
carbon resources .
3.2.3. REDUCED MORTALITY (DEATH) AND
MORBIDITY (DISEASE) DUE TO ELECTRIFICATION
In this section, we assess the human health impact
from emission reductions in the ambient PM2.5 levels
due to building electrification described in Section
3 .2 .2 . Using the U .S . EPA’s BenMAP community edition tool (BenMAP-CE), we estimated all-cause mortality
impacts, acute bronchitis impacts, and chronic bronchitis impactsvi due to the reduction in PM2.5 from the modeled electrification scenario for the year 2018, as described in Section 3 .2 .2 . As described in the Data and Methods section (Appendix A, Section A .2 .3), we incorporated impacts from the reduction of both primary and
secondary (nitrate) PM2.5 from the conversion of NOX to secondary PM2.5 .
For the year 2018 (as described in Section 3 .2 .2), the improvement in outdoor air quality from residential
building electrification alone would reduce approximately 354 deaths (all-cause mortality), 304 cases of chronic
bronchitis, and 596 cases of acute bronchitis in
California (see Table B-5 for confidence intervals for
mortality) . The most affected counties are the higher- population areas, i .e ., Los Angeles County and Orange County, due to the nature of the concentration-response function .
To estimate the monetized benefits of reduced all-cause mortality, we used a Value of a Statistical Life (VSL)
estimation in BenMAP, which is commonly used in health
impact assessment . For acute and chronic bronchitis,
we used a Willingness to Pay (WTP) function, explained
in more detail in Appendix A . The mortality reductions Mojave Desert
Northeast Plateau
South Coast
San Joaquin Valley
North Coast
Sacramento Valley
Great Basin Valleys
Mountain Counties
Salton Sea
South Central Coast
North Central Coast
San Diego County
San Francisco Bay
San Francisco Bay
Lake County Lake Tahoe
Sources: Esri, HERE, Garmin, Intermap, increment P Corp., GEBCO, USGS, FAO, NPS, NRCAN, GeoBase, IGN, Kadaster NL, Ordnance Survey, Esri Japan, METI, Esri China (Hong Kong), (c)
OpenStreetMap contributors, and the GIS User Community/ Total Reduction in
PM2.5
Concentrations
(μg/m3)
Air Basin
No data available
0.001 - 0.005
0.006 - 0.030
0.031 - 0.050
0.051 - 0.150
0.151 - 0.300
0.301 - 0.900
0 100 20050 Miles
Figure 3-3: Total reduction in ambient PM2.5 concentrations in California from elimination of gas appliances, by county in 2018 .
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 39 result in estimated monetized benefits of almost $3 .3 billion . For reductions of acute bronchitis and chronic bronchitis cases respectively, benefits were estimated at $310,000 and $150 million respectively, in 2019 dollar- values . The total estimated, monetized benefits for all health effects addressed (i .e ., all-cause mortality, acute bronchitis, and chronic bronchitis) were estimated to be close to $3 .5 billion dollars (see Table B-6 for confidence intervals for mortality) .
A summary of all health impact and valuation results
is shown in Table 3-1, and annual monetary values for
the five California air basins with the highest monetary benefits are shown in Table 3-2 . There are additional
tables in Appendix B describing health effects and
resulting monetary benefits by county and by air
basin . Tables B-3 and B-4 vii in the appendix include an approximation of mortality and valuation results by air basin for nitrate PM2.5 alone and all PM2.5 . For morbidity and the remainder of this discussion, this report only
refers to impacts from total PM2.5 .
Table 3-1: Annual health impacts and monetized benefits from outdoor air quality improvements in a residential electrification scenario .
Health Impact Avoided Mortality
and Morbidity Cases
(Annual)
Monetized Benefits
(Annual)
All-Cause Mortality
(ages 30 - 99)
354 $3.3 billion
Acute Bronchitis
(children ages 8-12)
596 $0.3 million
Chronic Bronchitis
(ages 27-99)
304 $150 million
Totals — $3.5 billion
Table 3-2 : Estimated annual monetization of health benefits from the electrification scenario by air basin for the five air basins with the highest benefits throughout the state .viii Air Basin All PM2.5 :
Mortality
Valuation
(Annual)
Acute
Bronchitis
Valuation
(Annual)
Chronic Bronchitis
Valuation
(Annual)
San
Francisco
Bay Area
$1.2 billion $100,000 $58 million
South Coast $1.0 billion 97,000 $46 million
Mojave
Desert
$0.6 billion 57,000 $26 million
Sacramento
Valley
$0.2 billion 16,000 $7 million
San Joaquin
Valley
$0.2 billion 18,000 $6 million
vii. We separated an air pollution impact of a county evenly across different air basins, in cases where the county is spread over different air basin areas. viii. The values in this table are rounded to two significant digits. Please see Table B-4 for detailed results.
A geographic depiction of mortality reductions by county is provided in Figure 3-4 .
We can compare our findings with other recently
released reports . As previously mentioned, EPRI released an analysis for the CEC on the air quality and health
impacts of a high electrification scenario in California .
In their analysis, EPRI found that electrification of
multiple sectors in 2050 would result in $108 billion in annual health benefits for California from reductions
in PM2.5 and ozone .15 They also found significant,
unexpected impacts from the reduction of residential
wood combustion — reductions in winter PM2.5 from
wood-burning are equivalent to reductions from all
other sources combined . More than half of EPRI’s
reported benefits would occur in the South Coast Air
Basin . The analysis involved developing a reference and electrification scenario for 2050 based on emission
inventories for non-road, stationary, on-road, and power- sector sources, pulled from multiple databases and
models . Though there are other challenges in comparison Mojave Desert
Northeast Plateau
South Coast
San Joaquin Valley
North Coast
Sacramento Valley
Great Basin Valleys
Mountain Counties
Salton Sea
South Central Coast
North Central Coast
San Diego County
San Francisco Bay
San Francisco Bay
Lake County Lake Tahoe
Sources: Esri, HERE, Garmin, Intermap, increment P Corp., GEBCO, USGS, FAO, NPS, NRCAN, GeoBase, IGN, Kadaster NL, Ordnance Survey, Esri Japan, METI, Esri China (Hong Kong), (c)
OpenStreetMap contributors, and the GIS User Community/ Total Reduction in
Cases of PM2.5 Related
All-Cause Mortality
(ages 30-99)
Air Basin
No data available
1 - 2
3 - 5
6 - 10
11 - 20
21 - 50
51 - 100
0 100 20050 Miles
Figure 3-4: Total reduction in annual cases of PM 2.5 related all- cause mortality by county in 2018 .
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 40 here as well, considering EPRI’s analysis is for 2050 and ours is for 2018, and our analysis only incorporates PM2.5 and residential building electrification, and is only including the effects of gas, it is reasonable to assume that our estimated benefits are a small percentage
of EPRI’s . Another general point of comparison is
CARB’s GHG inventory cited by the EPRI report, which
suggests that the residential sector was responsible
for approximately 6% of GHG emissions in 2017, most
of which resulted from gas combustion .289 This can be
compared to our residential sector findings of 3% ($3 .4 billion) of the monetized benefits EPRI estimated for high electrification of multiple sectors; however, again, our analysis only accounted for PM2.5 , and not ozone . Thus, they are even more comparable .
A Massachusetts Institute of Technology study
published in early 2020 assessed premature mortality
from cross-state air pollution in the U .S ., accounting for PM2.5 and ozone emissions and resulting health effects
from exposure .290 This analysis found that the residential and commercial sectors, which included residential
combustion of all fuels as well as other sources (such as waste treatment), were responsible for more than 6,000
premature deaths in California in 2018 .290 Our analysis accounts for a small subset of these mortality rates . We only assess PM2.5 and residential gas consumption in
our analysis; we do not include other fuels or emission sources, as the 2020 study did . Our findings account
for approximately 6% of these premature deaths
attributable to the residential and commercial sectors .
Another key finding from that particular study: The
premature deaths caused by those two sectors is
double the number caused by electric power generation
processes . The authors of that study clarify that this is a direct result of significant emission reductions in electric power generation processes since 2005 .290
We were not able to assess outdoor air quality and
resulting health effects at the census tract level due
to data paucity, but conducting future analyses at
that spatial level would enable us to draw quantitative conclusions about the relationship between gas
appliance use, electrification, and environmental justice .
3.2.4. ASSUMPTIONS AND LIMITATIONS
There are several limitations associated with the analysis presented in Section 3 . Data limitations restricted the geographical scale for this analysis, as much data (e .g ., on energy use) are only available at the county level
and higher . The RASS data we used to estimate total
emissions is from 2009, and therefore may not be
entirely representative of current usage proportions
of different appliances . Due to the limited scope of
this project, we were not able to conduct dispersion or photochemical modeling for the distribution of PM2.5
emissions and resulting ambient changes, and instead
used a back-of-the-envelope calculation for estimating
changes in PM2.5 at the county level that would result
from eliminating residential gas appliances . We also
assumed all indoor emissions from gas appliances
eventually traveled outdoors, which is a health-
protective, conservative assessment . We also did not
account for heating demand trends or seasonality in
this analysis, although prior studies have separately
evaluated winter and summer seasons . Considering
these factors, this is a simplified analysis and should be considered a conservative approximation .
Regarding the health impact analysis, it is important to note that the BenMAP software accounts for ambient
outdoor PM2.5 changes and does not assess population
time-activity patterns or personal exposures, which also significantly contribute to health effects .
Finally, there are several facets of electrification that we were unable to include in this report due to the scope of this project . There are some pollutant emissions from
the use of residential electric appliances, though not to the same extent as those produced by combustion of
gas appliances; we did not account for these electric
appliance emissions in this analysis . This report only focuses on residential buildings and does not include an assessment of the health and monetary impacts from
the electrification of commercial buildings . Also, it does not assess the costs and potential adverse impacts of
residential electrification as some other reports do, such as EPRI’s report (on electrification of multiple sectors), which we have discussed and cited .15
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 41 4 CONCLUSION
While California is a leader in clean energy and climate policy, many regions of the state have poor air quality, particularly in state-identified disadvantaged communities. As part of the state’s strategy to improve air quality and public health, one area of focus can be reducing emissions from gas appliances through methods such as building electrification. This report presents the adverse health effects resulting from the residential use of gas appliances and outlines the potential benefits of transitioning residential gas appliances to all-electric appliances. These benefits are not only related to GHG emission reductions, but also are related to improving indoor and outdoor air quality, as well as subsequent health and economic effects from pollutant reductions.
The indoor air quality analysis for this report found that concentrations of CO and NO2 during cooking events
can exceed the levels set by national and California-
based ambient air quality standards, occurring much
more often for NO2 than CO . Under a cooking scenario
where the stove and oven are used simultaneously for
an hour, acute exposures to NO2 from cooking with gas
appliances exceed the levels of national and California- based ambient air quality thresholds in more than 90%
of modeled emission scenarios . Concentrations of CO
and NO2 resulting from gas cooking are the highest
for apartments, due to smaller residence sizes . This
presents an additional risk for renters, who are often
lower income than homeowners . Considering the well-
known dangers of CO poisoning, and that acute and
chronic exposures to NO2 are associated with respiratory illness and mortality, this is a serious concern that should not be overlooked . We echo other researchers in this
space with the recommendation that proper ventilation
technology, such as effective, low-noise range hoods,
be implemented to reduce exposure and protect public
health .
Regarding outdoor air quality, this report indicates
that under a 2018 scenario where all residential gas
appliances were transitioned to electric, the reduction of secondary nitrate PM2.5 (from NOX) and primary PM2.5
would result in 354 fewer deaths, and 596 and 304
fewer cases of acute and chronic bronchitis, respectively .
The reduction in associated negative health effects is
equivalent to approximately $3 .5 billion in monetized
health benefits for just one year .
However, these health and monetary benefits will not be realized at the pace or scale needed without policymaker support . Decision-makers at state and local agencies
that regulate air quality all have important roles to play in determining the best course of action for reducing
pollution from gas appliances, and doing so in a way
that prioritizes and protects those most burdened by
air pollution — namely, low-income and environmental
justice communities . Implemented strategically, new
policies to reduce air pollution from residential buildings will yield significant health benefits, improve the quality of life for Californians, and reduce greenhouse gas
emissions .
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 42 APPENDICES
Appendix A: Data and Methods
A.1. INDOOR AIR QUALITY & HEALTH
EFFECTS (SECTION 2 IN THE REPORT)
A.1.1. EMISSION FACTOR DATABASE
We developed an EF database of CO, NO2, and NOX for
different gas appliances, including stoves and ovens,
heating devices, and water heaters . In cases where
EFs were not available for some pollutants (due to data paucity and/or feasibility), such as PM2.5 , UFP, and
formaldehyde, a qualitative analysis of related emissions and associated health impacts was conducted .
Aggregating appliance characteristics from online
resources
First, we summarized real-world (measured) EFs of
gas appliances from existing peer-reviewed or grey
literature . While most previous studies reported the EF of gas appliances in a unit such as ng/J, those values do not reflect the amount of pollutants released during the consumption without accounting for the MBR in J/h of
different gas appliances . Hence, we also summarized
the MBR of various gas and electric appliances from
approximately 15 main appliance brands using online
resources, including websites for companies such
as Home Depot, Lowe’s, Amazon, etc . Our internet
search terms to select brands and extract information
included, “gas and electric ovens,” “cooktops,” “popular gas appliances,” “range,” “gas range,” “electric range,” “furnace,” “water heater,” and “fireplace .” We gathered information regarding different models for each brand,
including price(s), heat output in British thermal units (BTUs — which were converted to J/h), and specification characteristics .
Extracting emission rates from primary literature and
determining significant explanatory variables
We acknowledge that the EF (ng/J) can be influenced
by many factors, such as appliance age, location, and
ventilation conditions . Thus, we collected information on these parameters in conjunction with EFs from the
aforementioned literature . We performed a multiple
linear regression analysis to quantify the contribution of different factors to the EFs of CO, NO2, and NOX, with
EFs and various factors as dependent and independent
variables, respectively . We ran three models using
RStudio software, with emission rates of CO, NO 2, and
NOX as the outcome variable .
Log (Emission Factor) = b0 + b1a + b2c + b3d + b4f + b5h + b6l (1)
EF (in a unit of ng/J) = f (a, c, d, f, l) * prediction uncertainty (2) Emission rate (in a unit of ng/h) = BTU* f (a, c, d, f, l) * prediction uncertainty
C = 𝑝𝑝% &
&'()*CO +
-
&'() (3)
𝛥𝛥𝑃𝑃𝑃𝑃1.3 45 = 𝑃𝑃𝑃𝑃1.3 (7894:;<)45 ∗ 𝑘𝑘 ∗
∆ABCDE
ABCDE
(4)
𝛥𝛥𝑃𝑃𝑃𝑃1.3 45 = 𝑃𝑃𝑃𝑃1.3 (7894:;<)45 ∗
∆FG1.3DE
FG1.3 (5)
(1)
where, a = appliance directly vented (yes/no), c = energy use (J/h), d = appliance age, f = appliance type, h =
laboratory or residence setting, and l = year of study .
The EFs from literature used as the outcome variable
in the regression analysis, along with the associated
covariates, were primarily extracted from a 2009
report produced by LBNL in California, which was ideal
since it provided very detailed information on sampling methods and results .44 Since this dataset is the most
recent source and specific to our study area, this was
our primary data source for the quantitative analysis .
We also gathered emission rates from other papers,
some of which dated to the 1970s (so, covering the last 50 years); we gathered as much data as was feasible
during the timeframe . We only used data from the
United States, and most data used was California-based, but we needed to use several other studies as well, to
optimize the regression models . Of course, there have
been technological advances that have reduced emission
rates over time, and this was factored into the regression model . Appliance ages spanned from 1-20 years old .
Most of the data used fit the regression line well .
Based on the results of normality tests, we log-
transformed the data . We ran the model with multiple
specifications, including with and without the oldest data points, and with various appliance groupings, to ensure our model was optimally fitted . The final sample sizes
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 43 (emission rates with values for each covariate in the regression equation), including all appliance types, were approximately 55 for each pollutant .
The regression models all had R2 values of ≥ 0 .6 (see
Figure B-1 in Appendix B), which indicates that the
models fit well, and the dependent variables of pollutant EFs in ng/J are highly predictable from the data . Three supplemental figures with the regression lines, J/second distribution (prior to conversion to J/h) and predicted emission rates are included in Appendix B (Figures B-1, B-2, and B-3) .
We identified factors that are significantly associated with EFs . Then, by reviewing existing literature and
databases, we obtained or assigned appropriate values
for those factors to better reflect the real-world scenario in California, and used bootstrapping statistics to
simulate the distribution of each factor — and thus,
EFs in California, accordingly, with 1000 bootstraps
for each factor . This nonparametric technique involved resampling data to estimate data distributions and is
widely used . The MBR values, in J/h, were gathered
from online resources and converted from BTU/h . The
ventilation characteristics we used for stoves and ovens were based on the general assumptions that stoves
and ovens are not vented, and heating devices and
water heaters are vented 44 (assumed due to existing
regulations) . According to California Health and Safety Code, gas-fueled, unvented space heaters cannot be
sold,76 the CEC mandates direct venting of water heaters to outside spaces,291 and the California Mechanical Code regulates the venting of other fuel-burning devices as
well (additional information on these types of regulations is provided in Section 2 .1 .2 of the report) .292 The age of appliances was gathered from the RASS . We calculated
EFs for stoves and ovens separately, but combined
them for much of this analysis under the assumption
that the devices were operating at the same time and
were entirely vented into the kitchen, though we do
include some separate considerations for stove use
only . We did not adjust for variable range hood use, due to survey results showing low rates of range hood use
in California .98 Therefore, this aspect of the analysis is more conservative .
Developing emission rate database
With available data on EFs (ng/J) and MBR (J/h), we
derived a new emission rate database for NO2, NOX, and
CO in a unit of ng/h, which we converted to µg/h, which reflects the emission rate, or the amount of pollutants ix. We took this approach because we believe it is valuable to compare cooking times of 15 minutes, 1 hour, and 2 hours, since one objective of this report is to help the public understand these concerns, and considering that some households may cook more or less than others, we wanted to provide this range. released in a specific time period during the usage of
different gas appliances . To validate our results, we
compared our calculated emission rates to the WHO’s
household fuel combustion emission rate targets293 as
well as primary literature . We used Microsoft Excel to conduct the bootstrapping and initial model setup . The equations used for calculating EFs and emission rates
are listed here:
Log (Emission Factor) = b0 + b1a + b2c + b3d + b4f + b5h + b6l (1)
EF (in a unit of ng/J) = f (a, c, d, f, l) * prediction uncertainty (2) Emission rate (in a unit of ng/h) = BTU* f (a, c, d, f, l) * prediction uncertainty
C = 𝑝𝑝% &
&'()*CO +
-
&'() (3)
𝛥𝛥𝑃𝑃𝑃𝑃1.3 45 = 𝑃𝑃𝑃𝑃1.3 (7894:;<)45 ∗ 𝑘𝑘 ∗
∆ABCDE
ABCDE
(4)
𝛥𝛥𝑃𝑃𝑃𝑃1.3 45 = 𝑃𝑃𝑃𝑃1.3 (7894:;<)45 ∗
∆FG1.3DE
FG1.3 (5)
(2)
where, a = appliance directly vented (yes/no), c = energy use (J/h), d = appliance age, f = appliance type, and l = year of study .
A.1.2. INDOOR AIR QUALITY IMPACTS AND
SUSCEPTIBILITY
We estimated the impact of the gas appliances that are
not vented to the outdoors (stoves and ovens) on indoor air quality using our developed EF database and a mass
balance model:122
Log (Emission Factor) = b0 + b1a + b2c + b3d + b4f + b5h + b6l (1)
EF (in a unit of ng/J) = f (a, c, d, f, l) * prediction uncertainty (2) Emission rate (in a unit of ng/h) = BTU* f (a, c, d, f, l) * prediction uncertainty
C = 𝑝𝑝% &
&'()*CO +
-
&'() (3)
𝛥𝛥𝑃𝑃𝑃𝑃1.3 45 = 𝑃𝑃𝑃𝑃1.3 (7894:;<)45 ∗ 𝑘𝑘 ∗
∆ABCDE
ABCDE
(4)
𝛥𝛥𝑃𝑃𝑃𝑃1.3 45 = 𝑃𝑃𝑃𝑃1.3 (7894:;<)45 ∗
∆FG1.3DE
FG1.3 (5)
(3)
where, V = volume of the indoor space (m3), Q =
ventilation rate (m3/h), S = emission rate (µg/h), C0 = outdoor concentration (µg/m3), C = indoor concentration (µg/m3), k = deposition rate (h-1), and p = penetration factor (unitless) .
We used values for deposition rate and penetration
factor from recent journal articles .47,52 For outdoor
concentrations, we used average California values from
the EPA’s Air Data portal for 2018 .294 The methods for determining volume and ventilation rate, which varied
for different housing types, are described later in this section .
For this analysis, we defined two indoor environments,
one with the use of gas appliances and one without, to
determine the contribution of gas appliances to indoor air pollution, the latter of which represents an electrification scenario; we assumed there were no emissions
of combustion pollutants with the use of electric
appliances . Under the assumption of a steady state, we calculated the increment of indoor levels of CO, NO2, and NOX due to gas appliance use by comparing C in models
with or without emissions (S) from gas appliance usage .
The elevation of pollutants’ concentrations due to gas
appliances was weighted by the time of their usage (e .g ., time-activity patterns) over 24 hours to estimate the
contribution to chronic exposures . We modeled the use
of kitchen appliances under three cooking scenarios: 15 minutes, 1 hour, and 2 hours per day .ix These timeframes
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 44 were chosen based on a cooking appliance use survey
indicating a total daily cooking time of around 1 hour for breakfast, lunch, dinner, and other meals, for both stoves and ovens, though we included multiple timeframes to
account for a wide range of cooking patterns .98 For CO, we also weighted the elevated concentrations over 8
hours for comparison with the national 8-hour standard
of 10 mg/m3 for both California and the EPA .295,296
The model also produced an output with the highest
concentration value, representing the emissions while
cooking; we used this to establish peak concentration
levels . For peak concentration levels, we used kitchen- specific volumes, and for values weighted by usage time, we used entire residence volumes under the assumption
that pollutants would mix into the residential space over time .
We modeled the increments of CO, NO2, and NOX due to
gas appliance use in three common residential building
types: SFHs, apartment buildings, and townhouses . As
shown in Equation (3), the relationship between C and
S is dependent on other building parameters associated
with indoor air quality, suggesting differential impacts of gas appliances in different building types . Therefore, we collected data on building design parameters (e .g ., air exchange rate and ventilation, residence volume) by housing type in California from regulatory standards,
AHS, primary literature, and various other reports on
building ventilation and other factors . To estimate kitch- en volume, we assumed kitchens occupied 10% of the
house volume . This is near the lower end of the range
found in our literature review, and hence, another conser- vative assumption . We used bootstrapping to simulate
the distributions of the various housing parameters, and incorporated them into Equation (3) to finalize our indoor air quality estimates . These findings were simplified into three boxplots, by pollutant (Figure 2-1) .
For assessing the impact these concentrations and
associated exposures may have on health, we stopped
evaluating NOX separately, since NO2 is established to
be the primary health concern out of the nitrogen oxides, as well as a main combustion pollutant with established ambient air quality standards .
As noted in Section 2 .2 .2, we used California
(CAAQS) and U .S . EPA ambient (outdoor - NAAQS) air
quality standards as a metric for health effects from
exposure . These standards are the maximum allowable
concentration of a pollutant present in outdoor air
that will not have a known, adverse impact on human
health and are developed to apply to long-term, ambient outdoor air quality, averaged over time periods . It is not possible to actually exceed these outdoor standards in
an indoor environment due to the technical definition .
Therefore, we apply target thresholds using the
standards as a guide to provide context for indoor air
quality . We refer to three different types of thresholds based on the standards: 1) Acute (1-hour for NO2 and
CO), 2) 8-hour (for CO), and 3) chronic (annual mean for NO2; there is no annual mean standard for CO) . When
we use the term “acute,” we are referring to 1-hour
standards . For CO, we refer to 8-hour standards directly as such . For NO2, when we use the term “chronic,” we are referring to the annual mean standards .
When an exceedance is referenced in this report, it
means that the modeled indoor air concentration is
higher than the threshold levels based on the standards in Table B-7 . When we refer to the percentage of
exceedances, we are discussing the percent of our
modeled indoor air quality estimates that exceed
thresholds . We evaluated the indoor air quality
exceedances of the CAAQS and NAAQS thresholds,
overall and for separate residence types, for CO and NO 2 (there are no applicable standards for NOX) .
To assess acute exposures of these two pollutants, we
compared peak concentrations to acute (1-hour) CAAQS
and NAAQS . This is like calculating a hazard quotient
(HQ) as is done in risk assessment, which would be a
ratio of the concentrations to the established standards .
If the HQ is less than 1 (essentially, if the maximum
concentration does not exceed the standard), adverse
health impacts are not expected . We compared the peak
concentrations to 1-hour CAAQS of 339 µg/m3 (180
ppb) for NO2 and 23 mg/m3 (20 ppm) for CO and 1-hour
NAAQS (US EPA standards) of 188 µg/m3 (100 ppb) for
NO2 and 40 mg/m3 (35 ppm) for CO .295 Exceedances
of the thresholds for our estimated peak concentrations (based on 1-hour standards) only apply under a scenario where cooking occurs for the entire hour and the air
quality levels remain elevated .
To assess chronic exposures, we compared chronic
exposure concentrations for NO2 to the annual mean
CAAQS (57 µg/m3 or 30 ppb) and NAAQS (100 µg/m3 or
53 ppb) as well .295,296 For CO, we compared our 8-hour averages to the 8-hour threshold of 10 mg/m3 (9 .0 ppm) for both CAAQS and the NAAQS .295 All acute, chronic,
and 8-hour standards are listed in Table B-7 . We also
qualitatively discussed long-term health impacts of the pollutants (Section 2 .2 .4) as described in the literature, since chronic impacts are less well-established for NO2 and CO (though the epidemiological literature on NO2
and mortality is expanding, which we discuss in detail in the results section) . More information on this is provided in Section A .1 .3 .
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 45 We conducted two sensitivity analyses: we estimated
indoor air concentrations due to potential use of kitchen appliances for supplemental heating, and we estimated
concentrations resulting from improper ventilation
systems for appliances required to be vented outdoors
(within the results, we discuss peak concentrations in the entire home due to the ventilation issues) .
We evaluated exposure susceptibility qualitatively
to the extent possible (Section 2 .2 .3), including
equity considerations . There is insufficient data to
quantitatively estimate exposure disparities in different groups . It is important to note that risk is highly
dependent on exposure parameters (e .g ., inhalation rate and body weight) . Additionally, different populations’ exposures are affected by their activity patterns as well as by the environmental concentrations of pollutants . We qualitatively discussed the exposure levels of populations with different characteristics .
A.1.3. HEALTH EFFECTS OF AIR POLLUTION
We reviewed previous human research studies focusing
on pollutants that could be emitted by gas appliances .
Specifically, controlled-exposure experimental and
time-series epidemiologic studies were reviewed to
evaluate the adverse health effects of short-term
exposures, while cross-sectional studies were reviewed
for long-term effects . In Section 2 .2 .4, we summarized potential outcomes associated with CO, NO2, and NOX
at all levels, including those comparable to our modeled concentrations . Additionally, we summarized the current literature on the health impacts of exposure to PM and
formaldehyde .
A.2. OUTDOOR AIR QUALITY & HEALTH
EFFECTS (SECTION 3 IN THE REPORT)
A.2.1. CONTRIBUTION TO TOTAL EMISSIONS OF
OUTDOOR AIR POLLUTANTS IN CALIFORNIA
We estimated the total emissions of outdoor air
pollutants from gas appliances in California, at the
county and state-wide levels . To do this, we used the
EF database created in Section 2 in combination with
total gas consumption (from the CEC) to calculate the
total emissions of CO, NO2, and NOX in tons/year .297
Since consumption patterns related to appliances vary
by region (e .g ., in some regions 40% of the energy may be used by water heaters, but in a different area, more energy is designated to heating devices than water
heaters), we used the RASS relative appliance energy
usage splits by climate zones to estimate emissions in
each county by assigning counties to each climate zone .
Total emissions of each pollutant by county are depicted in Figure B-4 . We compared the contributions from
gas appliances to NOX emissions with other sources
in California, which is shown in Figure B-5 . With the
data of energy consumption by different gas appliances
in California,287 we also estimated the emissions by
appliance type, and the result is depicted in Figure 3-1 .
It is also important to note that for this second section, we incorporated emissions from all types of appliances, while for the indoor air quality evaluation, we primarily considered emissions from appliances that are not
vented to the outdoors (e .g ., stoves and ovens), and also conducted a sensitivity analysis, incorporating scenarios in which venting technology for water heaters and
home heating devices failed to transport all combustion pollutants outdoors . For this section, we operated under the conservative assumption that all indoor emissions
are transporting outside .
A.2.2. EMISSION REDUCTION DUE TO
ELECTRIFICATION
We simulated NOX emissions (which include NO2) under
the assumption that all the energy generated by gas
appliance usage is replaced by clean electricity . We
modeled and evaluated an all-electrification scenario,
as compared to the “business as usual” scenario with
no replacement of appliances (though this scenario is
unrealistic, as normal replacement rates are a part of
“business as usual”) . This simulates 100% replacement
of gas appliances with electric appliances .
Our modeled scenario, which is for the year 2018, was
based on the assumption of adoption of entirely clean
electric technologies . We discussed the limitations
associated with this, with consideration to the emissions from electricity generation at power plants,298 and the reduction in EFs over time .
A.2.3. REDUCED AMBIENT PM2.5 CONCENTRATIONS
AND RESULTING MORTALITY AND MORBIDITY
IMPACTS DUE TO ELECTRIFICATION
Using the same scenario listed in Section A .2 .2 and
the previously calculated reduction in total outdoor
emissions, we estimated the potential mortality
and morbidity impacts (only for acute and chronic
bronchitis) in California due to residential building
electrification and the resulting reduction in ambient
outdoor concentrations of PM2.5 . This analysis was
entirely separate from the indoor air exposure analysis in Section 2 . Again, we operated under the conservative assumption that all indoor emissions are transported
outdoors .
Approximately 40% of NOX converts into nitrate-PM2.5
after emission . Thus, we first estimated reductions in
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 46 secondary PM2.5 levels by county (later aggregated to air basin) due to reduction in NOX and resulting nitrate PM2.5 , using methods described in a recently published paper .299
Log (Emission Factor) = b0 + b1a + b2c + b3d + b4f + b5h + b6l (1)
EF (in a unit of ng/J) = f (a, c, d, f, l) * prediction uncertainty (2) Emission rate (in a unit of ng/h) = BTU* f (a, c, d, f, l) * prediction uncertainty
C = 𝑝𝑝% &
&'()*CO +
-
&'() (3)
𝛥𝛥𝑃𝑃𝑃𝑃1.3 45 = 𝑃𝑃𝑃𝑃1.3 (7894:;<)45 ∗ 𝑘𝑘 ∗
∆ABCDE
ABCDE
(4)
𝛥𝛥𝑃𝑃𝑃𝑃1.3 45 = 𝑃𝑃𝑃𝑃1.3 (7894:;<)45 ∗
∆FG1.3DE
FG1.3 (5)
(4)
In Equation 4, i represents the year, j represents the
area of analysis (county), and k is the conversion rate for NOx to nitrate (0 .4) .300 ΔNOxij is the reduction in NOx emissions in that particular county and year, and NOxij is the total NOX emissions in county j in that year, extracted from CARB’s State Implementation Plan Standard
Emission Tool database .73 PM2.5ij is the nitrate PM2.5 level in each county, and was calculated by averaging nitrate PM2.5 data from the US EPA Air Data portal .294
We did not develop EFs for primary PM2.5 in our study,
due to data paucity and uncertainty regarding how much
gas combustion contributes to PM2.5 (our literature
review provided sufficient evidence of a relationship
between UFPs and gas combustion, but not solely PM 2.5
in papers published in recent decades, particularly for kitchen appliances) . Since we were not able to calculate EFs for PM2.5 for reasons stated previously, we extracted CARB estimates of emissions for PM2.5 from residential
gas appliances . We used Equation 5 shown here to
calculate changes in ambient PM2.5 levels; the baseline PM2.5 levels were extracted from the US EPA Air Data
portal:
Log (Emission Factor) = b0 + b1a + b2c + b3d + b4f + b5h + b6l (1)
EF (in a unit of ng/J) = f (a, c, d, f, l) * prediction uncertainty (2) Emission rate (in a unit of ng/h) = BTU* f (a, c, d, f, l) * prediction uncertainty
C = 𝑝𝑝% &
&'()*CO +
-
&'() (3)
𝛥𝛥𝑃𝑃𝑃𝑃1.3 45 = 𝑃𝑃𝑃𝑃1.3 (7894:;<)45 ∗ 𝑘𝑘 ∗
∆ABCDE
ABCDE
(4)
𝛥𝛥𝑃𝑃𝑃𝑃1.3 45 = 𝑃𝑃𝑃𝑃1.3 (7894:;<)45 ∗
∆FG1.3DE
FG1.3 (5)
(5)
We then summed the two changes in PM2.5 , with the final PM2.5 increase representing both changes in primary and secondary (nitrate) PM2.5 from gas use .
We used the EPA’s BenMAP tool to estimate the
mortality and morbidity (acute and chronic bronchitis)
impacts for the scenario as compared to “business as
usual,” using the standard U .S . EPA preloaded selections when possible . BenMAP uses established concentration-
response functions to quantify mortality from increased PM2.5 pollution . Inputs included: the change in PM2.5
calculated in Equation 5, population rates,301 incidence rates,302 and a b value,156,303 which represents the health impact per unit change of pollution and is drawn from
epidemiologic literature . We used California-specific
input values .
Additionally, we used our BenMAP mortality and
morbidity outputs to monetize the benefits of
electrification . This process was done using the
BenMAP software (it has VSL calculations and other
specific morbidity valuation functions as well), except for chronic bronchitis, which has a functionality issue within BenMAP that we confirmed with U .S . EPA staff .
We calculated valuation for chronic bronchitis manually .
As stated in Section 3 .2 .3, we used VSL estimates
for monetizing mortality benefits, which is standard
in health impact assessment literature . For acute and
chronic bronchitis, we used the WTP metric for valuing
illness . The U .S . EPA BenMAP manual defines WTP
as “the willingness of individuals to pay for a good or service, such as a reduction in the risk of illness,” and it is considered conservative .304 We adjusted all of the monetary outputs for inflation by converting them to
2019 dollars, using the Bureau of Labor Statistics’ CPI Inflation Calculator .
The mortality and valuation results are presented in
Tables 3-1 and 3-2 in the report, and Tables B-3 to B-6 in Appendix B .
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 47 Appendix B: Supplemental Figures and Tables
(a)
1e+00
1e+01
1e+03
1e+02
1e-01
Adjusted R-Squared: 0.73
p-value < .001
Predicted EFs of CO ( ng /J)
Measured EFs of CO (ng/J)
1e+01 1e+02 1e+031e+001e-01
Predicted EFs of CO ( ng /J)
(b)
1.0 10.0
100.0
0.1 Adjusted R-Squared: 0.82
p-value < .001
Measured EFs of NO 2 (ng/J)
10.0 100.01.00.1
Predicted EFs of NO 2 ( ng /J)
(c)
100
30 10
Adjusted R-Squared: 0.60
p-value < .001
Measured EFs of NO x (ng/J)
1003010
Predicted EFs of NO X ( ng /J)
Figure B-1: Relationship between predicted and measured EFs of (a) CO, (b) NO 2, and (c) NOX . (Blue line = correlation between predicted EFs and measured EFs .)
Figure B-2: Energy use histogram of (a) heating devices, (b) water heaters, (c) ovens, and (d) stoves, gathered from online resources . 0 10,000 20,000 30,000
2 0
4 4
8 (a)
Heater (Joules/s)
Frequency
3,000 3,500 4,000 4,500 5,000
2.5 0
5.0 7.5
(c)
Oven (Joules/s)
Frequency
0 20,000 40,000 60,000
1 2
4 3
5 0
(b)
Water Heater (Joules/s)
Frequency
0 2,000 4,000 6,000
5 10
0 (d)
Stove (Joules/s)
Frequency
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 48 Emission Rates ( µg/h)
(a)CO
1e+04
1e+06
1e+08
StoveOvenWater
Heater
Heater
(b)NO 2
StoveOvenWater
Heater
Heater
1e+04
1e+06
1e+08Emission Rates ( µg/h)
(c)NO x
StoveOvenWater
Heater
Heater
Emission Rates ( µg/h)
1e+04
1e+06
1e+08
Figure B-3: Predicted emission rates of (a) CO, (b) NO 2, and (c) NOX in μg/h for various gas appliances .
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 49 Figure B-4: Total emissions of air pollutants (a) CO, (b) NO2, and (c) NOx by county (gray outlines) in 2018 .
Mojave Desert
Northeast Plateau
South Coast
San Joaquin Valley
North Coast
Sacramento Valley
Great Basin Valleys
Mountain Counties
Salton Sea
South Central Coast
North Central Coast
San Diego County
San Francisco Bay
San Francisco Bay
Lake County Lake Tahoe
Sources: Esri, HERE, Garmin, Intermap, increment P Corp., GEBCO, USGS, FAO, NPS, NRCAN, GeoBase, IGN, Kadaster NL, Ordnance Survey, Esri Japan, METI, Esri China (Hong Kong), (c)
OpenStreetMap contributors, and the GIS User Community/ Total CO
Emissions
(tons/year)
Air Basin
No data available
1 - 15
16 - 50
51 - 100
101 - 200
201 - 1000
1,001 - 3,500
0 100 20050 Miles
(a)
(a)
Mojave Desert
Northeast Plateau
South Coast
San Joaquin Valley
North Coast
Sacramento Valley
Great Basin Valleys
Mountain Counties
Salton Sea
South Central Coast
North Central Coast
San Diego County
San Francisco Bay
San Francisco Bay
Lake County Lake Tahoe
Sources: Esri, HERE, Garmin, Intermap, increment P Corp., GEBCO, USGS, FAO, NPS, NRCAN, GeoBase, IGN, Kadaster NL, Ordnance Survey, Esri Japan, METI, Esri China (Hong Kong), (c)
OpenStreetMap contributors, and the GIS User Community/ Total NOX
Emissions
(tons/year)
Air Basin
No data available
1 - 20
21 - 50
51 - 250
251 - 500
501 - 1000
1,001 - 4,000
0 100 20050 Miles
(c)
(c)
Mojave Desert
Northeast Plateau
South Coast
San Joaquin Valley
North Coast
Sacramento Valley
Great Basin Valleys
Mountain Counties
Salton Sea
South Central Coast
North Central Coast
San Diego County
San Francisco Bay
San Francisco Bay
Lake County Lake Tahoe
Sources: Esri, HERE, Garmin, Intermap, increment P Corp., GEBCO, USGS, FAO, NPS, NRCAN, GeoBase, IGN, Kadaster NL, Ordnance Survey, Esri Japan, METI, Esri China (Hong Kong), (c)
OpenStreetMap contributors, and the GIS User Community/ Total NO2
Emissions
(tons/year)
Air Basin
No data available
1 - 5
6 - 10
11 - 25
26 - 50
51 - 100
101 - 620
0 100 20050 Miles
(b)
(b)
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 50 Figure B-5: NOX emissions from residential gas appliances as compared to NO X emissions from all sources (all California counties) . 0 25,000 50,000 75,000 100,000
CALAVERAS
AMADOR
SAN BENITO
YUBA
NAPA
TRINITY
LASSEN
NEVADA
EL DORADO
GLENN
TEHAMA
SUTTER
MARIN
COLUSA
YOLO
KINGS
MADERA
MENDOCINO
BUTTE
SONOMA
PLACER
HUMBOLDT
SANTA CRUZ
SOLANO
MERCED
SHASTA
STANISLAUS
TULARE
SAN LUIS OBISPO
SACRAMENTO
SAN JOAQUIN
SAN MATEO
VENTURA
SANTA CLARA
SAN FRANCISCO
CONTRA COSTA
ALAMEDA
MONTEREY
FRESNO
ORANGE
RIVERSIDE
SANTA BARBARA
KERN
SAN DIEGO
SAN BERNARDINO
LOS ANGELES
NO x Emisions in Tons/Year
County
NO x Emissions in Tons/Year (Gas Appliances) NO x Emissions in Tons/Year (Other Sources)
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 51 Table B-1: Pollutants other than CO, NO 2, and NOx emitted during gas appliance use as identified in various studies and reports, and a summary of associated key findings and health outcomes .
Pollutant Source Description of Study Key Findings Related to Pollutant Example of Health Impacts of Exposure to
Pollutant
Acetaldehyde
Fortmann, R., Kariher, P.
& Clayton, R. 2001 27
Assessed emissions of multiple
pollutants during typical stove and
oven use activities in a California home
(both gas and electric ranges).
Acetaldehyde is present in air samples
collected during fish broiling, oven
self-cleaning, and pork roast tests.
These findings, though limited, provide
evidence that cooking may have a
substantial effect on aldehyde levels
more broadly.
Carcinogenic, sensory
irritant, and affects the
respiratory system. 305,306
Mullen, N. A., Li, J. &
Singer, B. C. 2012 45
Concentrations of CO, NO X, NO2,
formaldehyde, and acetaldehyde
were measured over 6-day
periods in 155 California homes to
assess associations of pollutant
concentrations with natural gas
appliances.
The geometric mean of acetaldehyde
concentrations in both kitchens and
bedrooms was 9 ppb, which was much
higher than outdoor concentrations.
However, acetaldehyde concentrations
were not significantly affected by gas
appliance use.
Carcinogenic, sensory
irritant, and affects the
respiratory system. 305,306
Mullen, N. A. et al. 2016 46 To assess the indoor air quality impacts of gas appliance use,
collected indoor and outdoor
measurements of pollutants at 352
California homes with natural gas
appliances, and conducted interviews
with residents.
This study did not find statistically
significant changes in acetaldehyde
levels due to gas appliance use.
Carcinogenic, sensory
irritant, and affects the
respiratory system. 305,306
Singer, B. C. et al. 2009 44 Measured emission rates of multiple pollutants from natural gas
combustion in various types of stoves,
ovens, broilers, water heaters, and
furnaces. This was a large study with
multiple objectives.
Acetaldehyde emission rates were low
for all burners.
Carcinogenic, sensory
irritant, and affects the
respiratory system. 305,306
Formaldehyde
Fortmann, R., Kariher, P.
& Clayton, R. 2001 27
Assessed emissions of multiple
pollutants during typical stove and
oven use activities in a California home
(both gas and electric ranges).
Formaldehyde was present in
air samples collected during fish
broiling, oven self-cleaning, and pork
roast tests. This study reported
formaldehyde concentrations far
above the acute Reference Exposure
Level set by OEHHA during gas
cooking, both with and without food.
These findings, though limited, provide
evidence that cooking may have a
substantial effect on aldehyde levels
more broadly.
Carcinogenic, sensory
and respiratory
irritant, causes
nausea and headache.
103,200,201,206,307,308
Mullen, N. A., Li, J. &
Singer, B. C. 2012 45
Concentrations of CO, NO X , NO2,
formaldehyde, and acetaldehyde
were measured over 6-day
periods in 155 California homes to
assess associations of pollutant
concentrations with natural gas
appliances.
The geometric mean of formaldehyde
concentrations in both kitchens
and bedrooms was 15 ppb, which
was much higher than outdoor
concentrations. About 95% of homes
had indoor formaldehyde levels above
the Chronic Reference Exposure Level
set by OEHHA. However, formaldehyde
concentrations were not significantly
affected by gas appliance use.
Carcinogenic, sensory
and respiratory
irritant, causes
nausea and headache.
103,200,201,206,307,308
Mullen, N. A. et al. 2016 46 To assess the indoor air quality impacts of gas appliance use,
collected indoor and outdoor
measurements of pollutants at 352
California homes with natural gas
appliances, and conducted interviews
with residents.
This study did not find statistically
significant changes in formaldehyde
levels due to gas appliance use.
Carcinogenic, sensory
and respiratory
irritant, causes
nausea and headache.
103,200,201,206,307,308
Singer, B. C. et al. 2009 44 Measured emission rates of multiple pollutants from natural gas
combustion in various types of stoves,
ovens, broilers, water heaters, and
furnaces. This was a large study with
multiple objectives.
Formaldehyde emission rates showed
high variability across all burners, but
were particularly low in storage water
heaters and high in tankless water
heaters.
Carcinogenic, sensory
and respiratory
irritant, causes
nausea and headache.
103,200,201,206,307,308
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 52 Pollutant Source Description of Study Key Findings Related to Pollutant Example of Health Impacts of Exposure to
Pollutant
Polycyclic
Aromatic
Hydrocarbons
(PAHs)
Fortmann, R., Kariher, P.
& Clayton, R. 200 127
Assessed emissions of multiple
pollutants during typical stove and
oven use activities in a California home
(both gas and electric ranges).
PAHs were found in cooking oils
used, though PAH air concentrations
were low; the study concluded that
additional research on PAHs is
necessary in order to fully assess
the impact of cooking on PAH
concentrations.
Varies by PAH. Examples
are carcinogenic and
teratogenic effects, and
various impacts from
oxidative stress. 311,312
Ruiz, P. A. et al. 2010 66 Conducted indoor and outdoor sampling of 16 homes with unvented
space heaters using different energy
sources (electric/central heating,
compressed natural gas, liquified
petroleum gas, and kerosene) in Chile.
This study found high levels of PAHs in
homes with kerosene space heaters.
The impacts of gas space heaters were
less significant.
Varies by PAH. Examples
are carcinogenic and
teratogenic effects, and
various impacts from
oxidative stress. 311,312
Yu, K.-P. et al. 2015 241 Sampled particle concentrations and PAHs in five gas cooking kitchens of
non-smoking families in Taiwan and
conducted a health risk assessment.
This study found that PAH
concentrations were correlated with
PM concentrations, and PAH cooking
exposures could result in cancer
risks exceeding the well-established
threshold of 10 -6.
Varies by PAH. Examples
are carcinogenic and
teratogenic effects, and
various impacts from
oxidative stress. 311,312
Dutton, S. J., Hannigan,
M. P. & Miller, S. L.
200190
Monitored emissions of NO 2, CO,
and PAHs from unvented natural gas
fireplaces in two Colorado residences.
The concentrations measured here
were more than an order of magnitude
larger than ambient measurements in
urban areas. This study highlights the
need for research to assess the effects
of PAH exposure further.
Varies by PAH. Examples
are carcinogenic and
teratogenic effects, and
various impacts from
oxidative stress. 312,313
Sulfur Dioxide
(SO2)
Jones, A. P. 1999 23 This review paper assessed indoor air quality and health.
This review identifies that indoor SO 2
concentrations can be high in homes
with poorly vented gas appliances and
kerosene space heaters, citing studies
(before 2000) that have sampled
homes with both types of appliances.
Respiratory symptoms
and disease, premature
mortality. 313,314
Triche, E. W. et al.
2005315
Assessed respiratory symptoms and
exposures of almost 900 women
who used secondary heating devices,
including gas space heaters, during
winter.
A 10-ppb increase in SO 2 was
associated with an increase in
respiratory symptoms (wheezing and
chest tightness), though kerosene
heaters evaluated in this study were
the primary source of SO 2.
Respiratory symptoms
and disease, premature
mortality. 313,314
Table B-1: Pollutants other than CO, NO 2, and NOx emitted during gas appliance use as identified in various studies and reports, and a summary of associated key findings and health outcomes, cont .
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 53 Pollutant Source Description of Study Key Findings Related to Pollutant Example of Health Impacts of Exposure to
Pollutant
Ultrafine
Particles
(UFP)/Particle
Number (PN)
Dennekamp, M. et al.
200128
Measured UFP and nitrogen oxide
emissions from gas and electric stoves
and ovens in a laboratory chamber
with no ventilation.
Gas combustion alone and with
boiling water produced UFP in a peak
size range of 15-40 nm. Electric
stove coils also generate UFP. The
authors suggested that cooking in
kitchens with inadequate ventilation
could produce toxic particle number
concentrations.
Respiratory impacts,
cardiovascular
disease, various
impacts from oxidative
stress, neurological
impacts.199,316–318
Minutolo, P. et al.
2008319
Measured UFP emissions from
3 heater burners and 1 stove burner in
an experimental chamber.
UFP in the size range of 1 nm-10 nm
formed under all examined conditions,
but at very low mass concentrations.
Larger UFP (soot particles) are not
formed under the conditions studied.
A larger amount of particles were
ultimately emitted from the stove top
burner than heater burners.
Respiratory impacts,
cardiovascular
disease, various
impacts from oxidative
stress, neurological
impacts.199,316–318
Ruiz, P. A. et al. 2010 66 Conducted indoor and outdoor sampling of 16 homes with unvented
space heaters using different energy
sources (electric/central heating,
compressed natural gas, liquified
petroleum gas, and kerosene) in Chile.
Found higher levels of UFP in homes
with combustion heaters (including
gas heaters) than in homes with
electric heaters or central heating.
Respiratory impacts,
cardiovascular
disease, various
impacts from oxidative
stress, neurological
impacts.199,316–318
Wallace, L., Wang, F.,
Howard-Reed, C. &
Persily, A. 2008 320
Measured UFP emissions of a gas
stove, electric stove, and electric
toaster oven in a test house. 150 tests
were conducted.
Found larger particle number
concentrations than reported in
previous studies assessing larger
particles >10 nm, with the highest
concentrations occurring at a 5 nm
particle size. The study concludes
that gas and electric stoves produce
these small particles in significant
quantities.
Respiratory impacts,
cardiovascular
disease, various
impacts from oxidative
stress, neurological
impacts.199,316–318
Zhang, Q., Gangupomu,
R. H., Ramirez, D. & Zhu,
Y. 201057
Measured UFP, PM 2.5 , and black
carbon concentrations from cooking in
residences.
Cooking increased UFP concentrations
in the kitchen significantly. This
study found that the highest UFP
concentrations occurred when gas
stoves were turned on high and range
hoods were not on.
Respiratory impacts,
cardiovascular
disease, various
impacts from oxidative
stress, neurological
impacts.199,316–318
Other Volatile
Organic
Compounds
(VOCs)
Stocco, C. et al. 2008 323 Measured personal, indoor and outdoor 24-hour levels of 188 VOCs
(though analysis focused on 18) in
48 homes for 8 weeks during winter
and summer in Canada. Created an
exposure model using predictions
based on indoor concentrations.
Indoor concentrations of VOCs are
predictive of personal exposures.
Having a gas stove in the home was
a significant predictor of acrolein
exposure.
Varies by VOC. Examples
are headaches, fatigue,
respiratory issues. 321,322
Table B-1: Pollutants other than CO, NO 2, and NOx emitted during gas appliance use as identified in various studies and reports, and a summary of associated key findings and health outcomes, cont .
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 54 County PM2.5 Emissions from Gas
Appliances (tons/year) 73
Primary PM 2.5
Reduction ( µg/m3)
NOX Emissions from Gas
Appliances (tons/year)
Nitrate PM 2.5
Reduction ( µg/m3)
Total PM2.5
Reduction ( µg/m3)
Alameda 101 0.47 793 0.021 0.49
Alpine 0 0 0 0 0
Amador 0.77 0.0072 7.5 0.00081 0.0081
Butte 12 0.029 91 0.0031 0.032
Calaveras 0.22 0.0017 1.4 0.00023 0.0020
Colusa 0.80 0.0036 7.5 0.00051 0.0042
Contra Costa 77 0.29 634 0.018 0.30
Del Norte 0 0 0 0 0
El Dorado 1.2 0.0027 84 0.0025 0.0052
Fresno 44 0.045 368 0.018 0.062
Glenn 1.0 0.013 8.2 0.00070 0.014
Humboldt 7.0 0.0091 71 0.00071 0.0098
Imperial 1.9 0.0015 0 0 0.0015
Inyo 0 0 0 0 0
Kern 39 0.030 343 0.0133 0.043
Kings 6.7 0.067 53 0.0114 0.078
Lake 0 0 0 0 0
Lassen 0 0 3.9 0.00018 0.00018
Los Angeles 368 0.22 3883 0.041 0.26
Madera 3.1 0.018 29 0.0055 0.024
Marin 23 0.41 192 0.0086 0.41
Mariposa 0 0 0 0 0
Mendocino 2.7 0.0036 21 0.00027 0.0038
Merced 10 0.072 90 0.012 0.085
Modoc 0 0 0 0 0
Mono 0 0 0 0 0
Monterey 22 0.0086 181 0.0017 0.010
Napa 9.2 0.19 75 0.019 0.20
Nevada 2.1 0.013 48 0.0037 0.017
Orange 120 0.33 1178 0.041 0.37
Placer 18 0.025 229 0.0057 0.031
Plumas 0 0 0 0 0
Riverside 72 0.12 960 0.043 0.16
Table B-2 : Emissions of PM2.5 and NOX from residential gas appliance use and estimated primary, nitrate, and total PM 2.5 reductions under an electrification scenario in which all residential gas appliances are replaced with electric appliances .
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 55 Table B-2 : Emissions of PM2.5 and NOX from residential gas appliance use and estimated primary, nitrate, and total PM 2.5 reductions under an electrification scenario in which all residential gas appliances are replaced with electric appliances, cont .
County PM2.5 Emissions from Gas
Appliances (tons/year) 73
Primary PM 2.5
Reduction ( µg/m3)
NOX Emissions from Gas
Appliances (tons/year)
Nitrate PM 2.5
Reduction ( µg/m3)
Total PM2.5
Reduction ( µg/m3)
Sacramento 73 0.21 716 0.028 0.24
San Benito 2.2 0.032 23 0.0027 0.035
San Bernardino 80 0.062 857 0.0039 0.066
San Diego 62 0.057 942 0.016 0.073
San Francisco 65 0.84 512 0.015 0.85
San Joaquin 35 0.22 316 0.026 0.24
San Luis Obispo 14 0.051 132 0.0025 0.053
San Mateo 56 0.53 446 0.015 0.55
Santa Barbara 25 0.028 194 0.0014 0.029
Santa Clara 112 0.37 851 0.040 0.41
Santa Cruz 14 0.062 122 0.0031 0.065
Shasta 6.6 0.0064 61 0.00057 0.0070
Sierra 0 0 0 0 0
Siskiyou 0 0 0 0 0
Solano 27 0.22 205 0.0098 0.23
Sonoma 30 0.15 252 0.011 0.16
Stanislaus 26 0.16 220 0.022 0.19
Sutter 5.4 0.051 43 0.0031 0.054
Tehama 1.3 0.0023 13 0.0011 0.0034
Trinity 0 0 0.080 0.0000032 0.0000032
Tulare 21 0.043 181 0.016 0.060
Tuolumne 0 0 0 0 0
Ventura 41 0.12 344 0.0050 0.13
Yolo 10 0.064 91 0.0053 0.070
Yuba 2.6 0.044 26 0.0042 0.048
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 56 Table B-3: Estimated mortality and morbidity reductions from the electrification scenario by air basin, in 2018 .
Air Basin Nitrate PM 2.5 :
Reduced Mortality
All PM2.5 :
Reduced Mortality
Acute Bronchitis
(Cases Avoided)
Chronic Bronchitis
(Cases Avoided)
Great Basin Valleys 0 0 0 0
Lake County 0 0 0 0
Lake Tahoe 0.061 0.29 0.35 0.19
Mojave Desert 9.7 61 109 52
Mountain Counties 0.088 0.43 0.45 0.27
North Central Coast 0.063 0.91 1.5 0.76
North Coast 0.14 2.2 2.5 1.5
Northeast Plateau 0.0021 0.0024 0.0031 0.0017
Sacramento Valley 2.1 20 31 14
Salton Sea 1.4 5.4 9.9 4.1
San Diego 2.1 9.5 15 7.8
San Francisco Bay Area 6.0 125 196 115
San Joaquin Valley 2.8 18 35 13
South Central Coast 0.24 5.7 9.3 4.4
South Coast 14 105 185 91
Total 39 354 596 304
Table B-4 : Estimated monetization of the health benefits from the electrification scenario by air basin, in 2018 .
Air Basin Nitrate PM 2.5 :
Mortality Valuation
All PM2.5 :
Mortality Valuation
Acute Bronchitis Valuation Chronic Bronchitis Valuation Great Basin Valleys $0 $0 $0 $0
Lake County $0 $0 $0 $0
Lake Tahoe $565,809 $2,707,573 $185 $95,561
Mojave Desert $90,280,523 $570,844,734 $57,04 8 $26,344,390 Mountain Counties $818,583 $3,972,574 $239 $134,691
North Central Coast $592,105 $8,528,831 $808 $380,196
North Coast $1,332,509 $20,137,675 $1,331 $729,931
Northeast Plateau $20,055 $22,050 $2 $831
Sacramento Valley $19,919,241 $187,863,502 $16,487 $7,182,284 Salton Sea $13,247,57 1 $50,566,952 $5,187 $2,069,330
San Diego $19,4 47,260 $88,384,743 $8,138 $3,932,141
San Francisco Bay Area $56,225,767 $1,168,481,307 $103,155 $57,664,334 San Joaquin Valley $26,072,110 $168,161,417 $18,422 $6,390,438 South Central Coast $2,226,449 $53,269,838 $4,888 $2,206,735 South Coast $134,721,840 $983,223,898 $97,34 3 $45,569,735 Total $365 million $3.31 billion $0.31 million $153 million
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 57 County All PM2.5 : Reduced Mortality
(95% Confidence Interval)
San Benito 0.07 (0.05, 0.09)
San Bernardino 13.03 (8.8, 17.25)
San Diego 9.46 (6.39, 12.52)
San Francisco 28.64 (19.33, 37.93)
San Joaquin 7.79 (5.26, 10.31)
San Luis Obispo 0.79 (0.53, 1.05)
San Mateo 16.03 (10.82, 21.23)
Santa Barbara 0.54 (0.36, 0.71)
Santa Clara 25.35 (17.12, 33.56)
Santa Cruz 0.69 (0.47, 0.91)
Shasta 0.1 (0.06, 0.13)
Sierra 0 (0, 0)
Siskiyou 0 (0, 0)
Solano 4.54 (3.07, 6.01)
Sonoma 4.11 (2.78, 5.44)
Stanislaus 4.51 (3.05, 5.97)
Sutter 0.24 (0.16, 0.32)
Tehama 0.01 (0.01, 0.02)
Trinity 0 (0, 0)
Tulare 1.05 (0.71, 1.39)
Tuolumne 0 (0, 0)
Ventura 4.37 (2.95, 5.78)
Yolo 0.56 (0.38, 0.74)
Yuba 0.16 (0.11, 0.21)
County All PM2.5 : Reduced Mortality
(95% Confidence Interval)
Alameda 29.4 (19.85, 38.93)
Alpine 0 (0, 0)
Amador 0.02 (0.02, 0.03)
Butte 0.43 (0.29, 0.57)
Calaveras 0.01 (0, 0.01)
Colusa 0.003 (0.002, 0.004)
Contra Costa 14.58 (9.84, 19.29)
Del Norte 0 (0, 0)
El Dorado 0.05 (0.03, 0.07)
Fresno 2.5 (1.69, 3.31)
Glenn 0.02 (0.01, 0.03)
Humboldt 0.08 (0.05, 0.1)
Imperial 0.02 (0.02, 0.03)
Inyo 0 (0, 0)
Kern 1.5 (1.02, 1.99)
Kings 0.38 (0.26, 0.51)
Lake 0 (0, 0)
Lassen 0 (0, 0)
Los Angeles 96.88 (65.42, 128.22)
Madera 0.16 (0.11, 0.21)
Marin 5.17 (3.49, 6.85)
Mariposa 0 (0, 0)
Mendocino 0.02 (0.01, 0.03)
Merced 0.85 (0.58, 1.13)
Modoc 0 (0, 0)
Mono 0 (0, 0)
Monterey 0.15 (0.1, 0.2)
Napa 1.55 (1.04, 2.05)
Nevada 0.11 (0.07, 0.14)
Orange 44.89 (30.31, 59.42)
Placer 0.79 (0.53, 1.05)
Plumas 0 (0, 0)
Riverside 16.16 (10.91, 21.39)
Sacramento 16.04 (10.83, 21.23)
Table B-5: BenMAP outputs for estimated mortality reductions from the electrification scenario by county, in 2018 .
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 58 County All PM2.5 : Mortality Valuation
& 95% Confidence Interval
Estimate Lower Bound Upper Bound
San
Bernardino
$113,451,872 $10,524,312 $307,711,232
San Diego $82,344,448 $7,638,627 $223,339,872
San
Francisco
$249,324,048 $23,121,320 $676,267,520
San Joaquin $67,795,992 $6,288,626 $183,882,720
San Luis
Obispo
$6,890,559 $639,203 $18,688,990
San Mateo $139,580,336 $12,945,681 $378,590,528
Santa
Barbara
$4,701,954 $436,181 $12,752,904
Santa Clara $220,699,600 $20,470,320 $598,609,024
Santa Cruz $6,017,096 $558,174 $16,319,943
Shasta $835,539 $7 7,510 $2,266,194
Sierra $0 $0 $0
Siskiyou $0 $0 $0
Solano $39,542,172 $3,667,874 $107,249,936
Sonoma $35,786,860 $3,319,630 $97,063,968
Stanislaus $39,271,068 $3,642,793 $106,514,288
Sutter $2,117,348 $196,416 $5,742,799
Tehama $110,212 $10,224 $298,922
Trinity $0 $0 $0
Tulare $9,130,249 $846,966 $24,763,624
Tuolumne $0 $0 $0
Ventura $38,036,816 $3,528,387 $103,166,240
Yolo $4,857,377 $450,592 $13,174,484
Yuba $1,407,345 $130,553 $3,817,086
County All PM2.5 : Mortality Valuation
& 95% Confidence Interval
Estimate Lower Bound Upper Bound
Alameda $255,972,880 $23,741,228 $694,285,440
Alpine $0 $0 $0
Amador $202,040 $18,743 $5 47,983
Butte $3,7 74,240 $350,120 $10,236,708
Calaveras $54,529 $5,058 $147,895
Colusa $28,817 $2,673 $78,159
Contra Costa $126,885,312 $11,769,362 $344,151,744
Del Norte $0 $0 $0
El Dorado $448,354 $41,592 $1,216,049
Fresno $21,789,786 $2,021,323 $59,099,608
Glenn $174,319 $16,171 $472,799
Humboldt $687,856 $63,810 $1,865,639
Imperial $2 17,224 $20,151 $589,166
Inyo $0 $0 $0
Kern $13,099,088 $1,215,142 $35,528,120
Kings $3,329,755 $308,882 $9,031,176
Lake $0 $0 $0
Lassen $20,543 $1,906 $55,719
Los Angeles $843,326,528 $78,224,896 $2,287,352,832
Madera $1,362,471 $126,391 $3,695,370
Marin $45,046,368 $4,178,137 $122,180,416
Mariposa $0 $0 $0
Mendocino $180,162 $16,713 $488,643
Merced $7,4 40,247 $690,186 $20,179,928
Modoc $0 $0 $0
Mono $0 $0 $0
Monterey $1,315,226 $122,009 $3,567,224
Napa $13,453,159 $1,247,909 $36,488,836
Nevada $921,981 $85,529 $2,500,646
Orange $390,746,336 $36,243,116 $1,059,827,968
Placer $6,895,075 $639,627 $18,701,210
Plumas $0 $0 $0
Riverside $140,681,808 $13,049,800 $381,568,448
Sacramento $139,650,096 $12,953,712 $378,772,032
San Benito $613,641 $56,925 $1,664,352
Table B- 6: BenMAP outputs for estimated monetization of mortality reductions from the electrification scenario by county, in 2018 (shown in 2015 dollars, pre-inflation adjustments) .
EFFECTS OF RESIDENTIAL GAS APPLIANCES ON INDOOR AND OUTDOOR AIR QUALITY AND PUBLIC HEALTH IN CALIFORNIA 59 Table B-7: List of air quality standards
Air Pollutant Standard Averaging Time Concentration
CO
CAAQS
1-hour 23,000 µg/m3 (20 ppm)
8-hour 10,000 µg/m3 (9 ppm)
NAAQS
1-hour 40,000 µg/m3 (35 ppm)
8-hour 10,000 µg/m3 (9 ppm)
Health Canada Residential
Indoor Air Quality Guideline
1-hour 28,600 µg/m3 (25 ppm)
Health Canada Residential
Indoor Air Quality Guideline
24-hour 11,500 µg/m3 (10 ppm)
NO2
CAAQS
1-hour 339 µg/m3 (180 ppb)
Annual mean 57 µg/m3 (30 ppb)
NAAQS
1-hour 188 µg/m3 (100 ppb)
Annual mean 100 µg/m3 (53 ppb)
Health Canada Residential
Indoor Air Quality Guideline
1-hour 170 µg/m3 (90 ppb)
Health Canada Residential
Indoor Air Quality Guideline
24-hour 20 µg/m3 (11 ppb)
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