Clean Air Act Issues in the 117th Congress

Changes from February 17, 2021 to November 23, 2021

This page shows textual changes in the document between the two versions indicated in the dates above. Textual matter removed in the later version is indicated with ~~red strikethrough~~ and textual matter added in the later version is indicated with blue.

Clean Air Act Issues in the 117th Congress
~~February 17~~November 23, 2021 , 2021
Congress may examine wide-ranging air pollution issues as it deliberates legislation and conducts Congress may examine wide-ranging air pollution issues as it deliberates legislation and conducts
oversight of the U.S. Environmental Protection Agency (EPA). Oversight of EPA’s air pollution oversight of the U.S. Environmental Protection Agency (EPA). Oversight of EPA’s air pollution
Kate C. Shouse
work has historically received significant attention in Congress. Such oversight has often work has historically received significant attention in Congress. Such oversight has often
Analyst in Environmental Analyst in Environmental
examined whether EPA’s programs meet the statutory objective to protect human health and the examined whether EPA’s programs meet the statutory objective to protect human health and the
Policy Policy
environment from air pollution, how evolving scientific understanding informs Clean Air Act environment from air pollution, how evolving scientific understanding informs Clean Air Act

(CAA) decisionmaking, and the degree to which potential tradeoffs exist between public health (CAA) decisionmaking, and the degree to which potential tradeoffs exist between public health
benefits and compliance costs. Some Members of Congress have also raised concerns about benefits and compliance costs. Some Members of Congress have also raised concerns about

potential disproportionate impacts on communities located near sources of emissions, and related potential disproportionate impacts on communities located near sources of emissions, and related
concerns about whether CAA standards are protective of vulnerable individuals (e.g., children, pregnant women, the elderly, concerns about whether CAA standards are protective of vulnerable individuals (e.g., children, pregnant women, the elderly,
and persons with preexisting health conditions). and persons with preexisting health conditions).
Congress may also consider legislation to address air pollution issues and EPA’s CAA authority. Recent Administrations Congress may also consider legislation to address air pollution issues and EPA’s CAA authority. Recent Administrations
have interpreted CAA authority in different, and sometimes conflicting, ways. Historically, many of EPA’s CAA regulations have interpreted CAA authority in different, and sometimes conflicting, ways. Historically, many of EPA’s CAA regulations
have been challenged in court, both by industry and by public health and environmental groups, with various states have been challenged in court, both by industry and by public health and environmental groups, with various states
supporting each side. supporting each side.
Some prominent air topics of potential interest in the 117th Congress are air quality standards, wildfire smoke, hazardous air Some prominent air topics of potential interest in the 117th Congress are air quality standards, wildfire smoke, hazardous air
pollutant standards, and permits. Related issues, such as greenhouse gas (GHG) emissions or other climate change topics pollutant standards, and permits. Related issues, such as greenhouse gas (GHG) emissions or other climate change topics
relevant to the CAA, are not addressed herein. relevant to the CAA, are not addressed herein.
Air Quality Standards
The CAA requires EPA to review national ambient air quality standards (NAAQS) for common pollutants every five years. The CAA requires EPA to review national ambient air quality standards (NAAQS) for common pollutants every five years.
~~The NAAQS review process has evolved over time. In recent years, EPA restructured the NAAQS review process by~~
~~compressing the schedule and disbanding a pollutant-specific scientific review panel that has historically advised agency staff~~
~~during their reviews.~~ In December 2020, EPA completed its particulate matter and ozone reviews, and finalized rules to retain In December 2020, EPA completed its particulate matter and ozone reviews, and finalized rules to retain
the current PM and ozone standards. While some supported EPA’s the current PM and ozone standards. While some supported EPA’s ~~efforts to streamline NAAQS reviews, others voiced~~
~~concerns that procedural changes compromised the agency’s review of the latest science~~decisions to retain the existing PM and ozone standards, others voiced concerns that the agency’s efforts to streamline the review procedures compromised its review of the latest science. In 2021, EPA announced that it would reconsider the 2020 decision to retain the PM and ozone standards. Congress may consider whether . Congress may consider whether
EPA’s review process meets the CAA objectives to review in a timely manner the NAAQS and the science upon which they EPA’s review process meets the CAA objectives to review in a timely manner the NAAQS and the science upon which they
are based. are based.
Wildfire Smoke
Wildfire smoke can temporarily increase ambient levels of particulate matter and other air pollutants. These increases may be Wildfire smoke can temporarily increase ambient levels of particulate matter and other air pollutants. These increases may be
measured by the national network of stationary air monitors. Given the need for real-time air quality information during measured by the national network of stationary air monitors. Given the need for real-time air quality information during
wildfire events, monitoring strategies may include some combination of stationary monitors, mobile sensors, or computer wildfire events, monitoring strategies may include some combination of stationary monitors, mobile sensors, or computer
modeling to estimate pollution levels. Congress may consider which monitoring strategies effectively inform smoke modeling to estimate pollution levels. Congress may consider which monitoring strategies effectively inform smoke
management and public health responses. Congress may also examine how CAA requirements factor into forest management management and public health responses. Congress may also examine how CAA requirements factor into forest management
and fire prevention strategies. and fire prevention strategies.
Hazardous Air Pollutants
The CAA requires EPA to set and periodically review standards limiting hazardous air pollutants (HAPs). Congress may The CAA requires EPA to set and periodically review standards limiting hazardous air pollutants (HAPs). Congress may
conduct oversight of EPA’s statutorily mandated reviews of regulations to limit HAPs such as ethylene oxide. Another CAA conduct oversight of EPA’s statutorily mandated reviews of regulations to limit HAPs such as ethylene oxide. Another CAA
issue involves the potential tension between incentivizing pollution prevention and limiting cumulative emissions. Under a issue involves the potential tension between incentivizing pollution prevention and limiting cumulative emissions. Under a
2020 EPA rulemaking, major sources of HAPs can reclassify as “area sources,” which are typically subject to lesser controls, 2020 EPA rulemaking, major sources of HAPs can reclassify as “area sources,” which are typically subject to lesser controls,
after meeting conditions to limit emissions below major source thresholds. Congress may consider the health and after meeting conditions to limit emissions below major source thresholds. Congress may consider the health and
environmental implications of this rule, including how potential HAP increases may contribute to cumulative exposures in environmental implications of this rule, including how potential HAP increases may contribute to cumulative exposures in
communities with relatively high environmental burdens. communities with relatively high environmental burdens.
CAA Permitting
Congress may conduct oversight of New Source Review (NSR), a CAA preconstruction permitting program intended to Congress may conduct oversight of New Source Review (NSR), a CAA preconstruction permitting program intended to
ensure that new and modified stationary sources of air pollution do not significantly degrade air quality. The NSR program ensure that new and modified stationary sources of air pollution do not significantly degrade air quality. The NSR program
generally requires emission limits based on modern pollution controls when new facilities are built or when existing facilities generally requires emission limits based on modern pollution controls when new facilities are built or when existing facilities
make a change that increases emissions above specified thresholds. Historically, NSR applicability determinations have been make a change that increases emissions above specified thresholds. Historically, NSR applicability determinations have been
contentious and extensively litigated. Congress may consider legislative proposals addressing questions about NSR contentious and extensively litigated. Congress may consider legislative proposals addressing questions about NSR
applicability and enforcement. applicability and enforcement.
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Clean Air Act Issues in the 117th Congress

Introduction
The 117th Congress is likely to face wide-ranging air pollution issues as it conducts oversight and The 117th Congress is likely to face wide-ranging air pollution issues as it conducts oversight and
deliberates on legislation related to air quality standards, smoke from wildfires, air quality deliberates on legislation related to air quality standards, smoke from wildfires, air quality
monitoring, air toxics, and permitting requirements. Congress may factor multiple issues into monitoring, air toxics, and permitting requirements. Congress may factor multiple issues into
these deliberations, including environmental and public health objectives, economic impacts, and these deliberations, including environmental and public health objectives, economic impacts, and
how the U.S. Environmental Protection Agency (EPA) accounts for how the U.S. Environmental Protection Agency (EPA) accounts for distributional effects1 in 1 in
benefit-cost analysis for Clean Air Act (CAA) rulemakings. benefit-cost analysis for Clean Air Act (CAA) rulemakings.
Diverse sources of air emissions—including power plants, industrial facilities, small commercial Diverse sources of air emissions—including power plants, industrial facilities, small commercial
facilities, motor vehicles, and wildfires—contribute to the various gaseous and particle pollutants facilities, motor vehicles, and wildfires—contribute to the various gaseous and particle pollutants
in ambient, or outdoor, air, which is the purview of the Clean Air Act. Air quality has improved in ambient, or outdoor, air, which is the purview of the Clean Air Act. Air quality has improved
substantially since Congress enacted the CAA in 1970. Annual emissions of the six “criteria” air substantially since Congress enacted the CAA in 1970. Annual emissions of the six “criteria” air
pollutants for which the EPA has set air quality standards—ozone, particulate matter, sulfur pollutants for which the EPA has set air quality standards—ozone, particulate matter, sulfur
dioxide, carbon monoxide, nitrogen dioxide, and lead—have since declined by more than 70%, dioxide, carbon monoxide, nitrogen dioxide, and lead—have since declined by more than 70%,
despite increases in population, motor vehicle miles traveled, and economic activity.2 despite increases in population, motor vehicle miles traveled, and economic activity.2
At the same time, EPA has tightened air quality standards as the scientific understanding of the At the same time, EPA has tightened air quality standards as the scientific understanding of the
health effects of air pollution has evolved. The goal of clean air continues to elude many areas.3 health effects of air pollution has evolved. The goal of clean air continues to elude many areas.3
For example, approximately For example, approximately ~~122~~125 million people live in 50 areas of the United States that do not million people live in 50 areas of the United States that do not
meet the ozone standards issued by EPA in 2015.4 Additionally, some Members of Congress have meet the ozone standards issued by EPA in 2015.4 Additionally, some Members of Congress have
expressed concern about wildfire smoke and air quality, including potential interactions with the expressed concern about wildfire smoke and air quality, including potential interactions with the
Coronavirus Disease 2019 (COVID-19).5 Exposure to smoke can increase the risk and severity of Coronavirus Disease 2019 (COVID-19).5 Exposure to smoke can increase the risk and severity of
respiratory infections such as COVID-19.6 respiratory infections such as COVID-19.6
This report begins with background about the CAA framework, including federal and state roles, This report begins with background about the CAA framework, including federal and state roles,
and summarizes congressional actions related to the CAA in the 116th and earlier Congresses. The and summarizes congressional actions related to the CAA in the 116th and earlier Congresses. The
report also discusses some prominent air topics of potential interest in the 117th Congress: EPA’s report also discusses some prominent air topics of potential interest in the 117th Congress: EPA’s
review of particulate matter and ozone standards; management of wildfire smoke; EPA’s review review of particulate matter and ozone standards; management of wildfire smoke; EPA’s review
of hazardous air pollutant standards; classification of hazardous air pollutant sources; and of hazardous air pollutant standards; classification of hazardous air pollutant sources; and
revisions to applicability determinations under the preconstruction permitting program, known as revisions to applicability determinations under the preconstruction permitting program, known as
New Source Review (NSR). This report does not discuss greenhouse gas (GHG) emissions or New Source Review (NSR). This report does not discuss greenhouse gas (GHG) emissions or
other climate change topics relevant to the CAA, which are addressed in other CRS reports.7 other climate change topics relevant to the CAA, which are addressed in other CRS reports.7

1 The Office of Management and Budget refers to 1 The Office of Management and Budget refers to distributional effects as “the impact of a regulatory action across the as “the impact of a regulatory action across the
population and economy, divided up in various ways (e.g., income groups, race, sex, industrial sector, geography).” See population and economy, divided up in various ways (e.g., income groups, race, sex, industrial sector, geography).” See
OMB Circular A-4, “Regulatory Analysis,” September 17, 2003, p. 14. OMB Circular A-4, “Regulatory Analysis,” September 17, 2003, p. 14.
2 EPA, 2 EPA, Our Nation’s Air, https://gispub.epa.gov/air/trendsreport/2020/#home. , https://gispub.epa.gov/air/trendsreport/2020/#home.
3 For example, see EPA’s Green Book for a list of areas that do not meet one or more of the NAAQS. EPA, 3 For example, see EPA’s Green Book for a list of areas that do not meet one or more of the NAAQS. EPA, Green
Book National Area and County-Level Multi-Pollutant Information, https://www.epa.gov/green-book/green-book-, https://www.epa.gov/green-book/green-book-
national-area-and-county-level-multi-pollutant-information. national-area-and-county-level-multi-pollutant-information.
4 Data reported by EPA as of 4 Data reported by EPA as of ~~December 31, 2020~~October 31, 2021, based on 2010 population. EPA, , based on 2010 population. EPA, 8-Hour Ozone (2015)
Nonattainment Area Summary, , ~~December 31, 2020~~October 31, 2021, https://www3.epa.gov/airquality/greenbook/jnsum.html. , https://www3.epa.gov/airquality/greenbook/jnsum.html.
5 Letter from Jeffrey A. Merkley, U.S. Senator, et al. to Alex M. Azar II, Secretary, U.S. Department of Health and 5 Letter from Jeffrey A. Merkley, U.S. Senator, et al. to Alex M. Azar II, Secretary, U.S. Department of Health and
Human Services, September 14, 2020. Human Services, September 14, 2020.
6 Centers for Disease Control and Prevention, 6 Centers for Disease Control and Prevention, FAQs for Wildland Firefighters, https://www.cdc.gov/coronavirus/2019-, https://www.cdc.gov/coronavirus/2019-
ncov/community/wildland-firefighters-faq.html. ncov/community/wildland-firefighters-faq.html.
7 For example, see (1) CRS In Focus IF11696, 7 For example, see (1) CRS In Focus IF11696, Aviation and Climate Change, by Richard K. Lattanzio; (2) CRS In , by Richard K. Lattanzio; (2) CRS In
Focus IF10752, Focus IF10752, Methane Emissions: A Primer, by Richard K. Lattanzio; (3) CRS In Focus IF10871, , by Richard K. Lattanzio; (3) CRS In Focus IF10871, Vehicle Fuel
Economy and Greenhouse Gas Standards, by Richard K. Lattanzio, Linda Tsang, and Bill Canis; (4) CRS Report , by Richard K. Lattanzio, Linda Tsang, and Bill Canis; (4) CRS Report
R46568, R46568, EPA’s Affordable Clean Energy Rule: In Brief, coordinated by Kate C. Shouse; and (5) CRS In Focus , coordinated by Kate C. Shouse; and (5) CRS In Focus
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Overview of the Clean Air Act
The CAA, codified as 42 U.S.C. 7401 et seq., seeks to protect human health and the environment The CAA, codified as 42 U.S.C. 7401 et seq., seeks to protect human health and the environment
from emissions that pollute ambient, or outdoor, air.8 It establishes roles for federal and state from emissions that pollute ambient, or outdoor, air.8 It establishes roles for federal and state
agencies and “expressly delegates a large number and variety of regulatory and policymaking agencies and “expressly delegates a large number and variety of regulatory and policymaking
functions.”9 For example, the act requires EPA to establish minimum national standards for air functions.”9 For example, the act requires EPA to establish minimum national standards for air
quality, known as national ambient air quality standards (NAAQS). States have primary quality, known as national ambient air quality standards (NAAQS). States have primary
responsibility for assuring compliance with these standards, and for establishing and responsibility for assuring compliance with these standards, and for establishing and
incorporating procedures in state implementation plans to attain and maintain the NAAQS. The incorporating procedures in state implementation plans to attain and maintain the NAAQS. The
CAA also requires that areas not meeting the standards, referred to as “nonattainment areas,” CAA also requires that areas not meeting the standards, referred to as “nonattainment areas,”
implement specified air pollution control measures. implement specified air pollution control measures.
Under the CAA, Congress mandated that EPA establish two types of NAAQS for each criteria Under the CAA, Congress mandated that EPA establish two types of NAAQS for each criteria
pollutant—a primary NAAQS, which must protect public health with an “adequate margin of pollutant—a primary NAAQS, which must protect public health with an “adequate margin of
safety,” and a secondary NAAQS, which must “protect public welfare from any known or safety,” and a secondary NAAQS, which must “protect public welfare from any known or
anticipated adverse effects.”10 Public welfare includes damage to crops, vegetation, property, anticipated adverse effects.”10 Public welfare includes damage to crops, vegetation, property,
building materials, and climate.11 building materials, and climate.11
The CAA also requires EPA to review the NAAQS and the science upon which they are based The CAA also requires EPA to review the NAAQS and the science upon which they are based
every five years and then revise the NAAQS if necessary. In addition, the CAA requires EPA to every five years and then revise the NAAQS if necessary. In addition, the CAA requires EPA to
appoint an independent scientific review committee composed of seven members, which has appoint an independent scientific review committee composed of seven members, which has
become the Clean Air Scientific Advisory Committee (CASAC). The act directs CASAC to become the Clean Air Scientific Advisory Committee (CASAC). The act directs CASAC to
review the NAAQS every five years and recommend to the EPA Administrator “any new national review the NAAQS every five years and recommend to the EPA Administrator “any new national
ambient air quality standards and revisions … as may be appropriate.”12 In practice, CASAC has ambient air quality standards and revisions … as may be appropriate.”12 In practice, CASAC has
evaluated the agency’s work during NAAQS-setting and NAAQS-revision, rather than evaluated the agency’s work during NAAQS-setting and NAAQS-revision, rather than
conducting its own independent review of the standards. Beyond these CAA requirements, conducting its own independent review of the standards. Beyond these CAA requirements,
procedural aspects of the NAAQS review are generally at the discretion of the EPA Administrator. procedural aspects of the NAAQS review are generally at the discretion of the EPA Administrator.
The CAA also includes provisions related to ambient air quality monitoring. The act requires EPA The CAA also includes provisions related to ambient air quality monitoring. The act requires EPA
to develop standards for the design and operation of an air quality monitoring network. It also to develop standards for the design and operation of an air quality monitoring network. It also
requires state implementation plans to “provide for establishment and operation” of the requires state implementation plans to “provide for establishment and operation” of the
monitors.13 States, local agencies, and tribes typically design and operate air quality monitoring monitors.13 States, local agencies, and tribes typically design and operate air quality monitoring
networks based on federal standards. networks based on federal standards.
The CAA contains air pollution provisions beyond the NAAQS requirements. The act establishes The CAA contains air pollution provisions beyond the NAAQS requirements. The act establishes
federal standards for certain new and modified stationary sources of air pollution, for mobile federal standards for certain new and modified stationary sources of air pollution, for mobile
sources of air pollution and their fuels, and for sources of 187 hazardous air pollutants.sources of air pollution and their fuels, and for sources of 187 hazardous air pollutants.14 It It
~~establishes a cap-and-trade program for the emissions that contribute to acid rain. It also~~
~~addresses protection of the stratospheric ozone layer.~~

IF11541, IF11541, Hydrofluorocarbons (HFCs): EPA and State Actions, by Kate C. Shouse. , by Kate C. Shouse.
8 For example, one of the stated purposes of Title I of the CAA is to “to protect and enhance the quality of the Nation’s 8 For example, one of the stated purposes of Title I of the CAA is to “to protect and enhance the quality of the Nation’s
air resources so as to promote the public health and welfare and the productive capacity of its population” (42 U.S.C. air resources so as to promote the public health and welfare and the productive capacity of its population” (42 U.S.C.
§7401(b)(1)). §7401(b)(1)).
9 Michael R. Barr, “Introduction to the Clean Air Act,” in 9 Michael R. Barr, “Introduction to the Clean Air Act,” in The Clean Air Act Handbook, ed. Julie R. Domike and Alec , ed. Julie R. Domike and Alec
C. Zacaroli, 4th ed. (Chicago: American Bar Association, 2016). C. Zacaroli, 4th ed. (Chicago: American Bar Association, 2016).
10 42 U.S.C. §7409(b). 10 42 U.S.C. §7409(b).
11 42 U.S.C. §7602(h). 11 42 U.S.C. §7602(h).
12 42 U.S.C. §7409(d)(2). 12 42 U.S.C. §7409(d)(2).
13 42 U.S.C. §§7410(a)(2)(B) and 7619. 13 42 U.S.C. §§7410(a)(2)(B) and 7619.
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14 As of this report’s publication date, there are 187 pollutants on the CAA’s list of hazardous air pollutants. EPA reported that it intends to add 1-bromopropane (1-BP) to the CAA’s list of hazardous air pollutants by the end of 2021. See EPA, Petitions to Add 1-BP (nPB) to the Clean Air act List of Hazardous Air Pollutants, https://www.epa.gov/ Congressional Research Service 2 Clean Air Act Issues in the 117th Congress establishes a cap-and-trade program for the emissions that contribute to acid rain. It also addresses protection of the stratospheric ozone layer. In addition, the CAA establishes two types of permits. One is New Source Review (NSR), a In addition, the CAA establishes two types of permits. One is New Source Review (NSR), a
preconstruction permit issued before construction of a new facility or major modification to an preconstruction permit issued before construction of a new facility or major modification to an
existing facility. The NSR program generally requires emission limits based on modern pollution existing facility. The NSR program generally requires emission limits based on modern pollution
controls when new facilities are built or when existing facilities make a change that increases controls when new facilities are built or when existing facilities make a change that increases
emissions above specified thresholds. Historically, NSR applicability determinations have been emissions above specified thresholds. Historically, NSR applicability determinations have been
contentious and extensively litigated.contentious and extensively litigated.1415
The second type of CAA permit is an operating permit required under Title V. The operating The second type of CAA permit is an operating permit required under Title V. The operating
permit is federally enforceable and specifies each source’s emission limits, compliance schedule, permit is federally enforceable and specifies each source’s emission limits, compliance schedule,
reporting requirements, and other conditions. States typically administer operating permit reporting requirements, and other conditions. States typically administer operating permit
programs and issue the permits. Sources subject to the permit requirements include major sources programs and issue the permits. Sources subject to the permit requirements include major sources
that emit or have the potential to emit 100 tons per year of any regulated pollutant, as well as that emit or have the potential to emit 100 tons per year of any regulated pollutant, as well as
sources that emit or have potential to emit lesser specified amounts of hazardous air pollutants.sources that emit or have potential to emit lesser specified amounts of hazardous air pollutants.1516
For more information about the CAA’s major requirements, see CRS Report RL30853, For more information about the CAA’s major requirements, see CRS Report RL30853, Clean Air
Act: A Summary of the Act and Its Major Requirements, by Kate C. Shouse and Richard K. , by Kate C. Shouse and Richard K.
Lattanzio. Lattanzio.
Air Pollution Issues in Prior Sessions of Congress
Oversight of EPA’s air pollution work has historically received significant attention from Oversight of EPA’s air pollution work has historically received significant attention from
Congress. Such oversight has often examined whether EPA’s programs meet the statutory Congress. Such oversight has often examined whether EPA’s programs meet the statutory
objective to protect human health and the environment from air pollution, whether EPA objective to protect human health and the environment from air pollution, whether EPA
regulatory efforts are consistent with, or exceed, the agency’s statutory authority, how evolving regulatory efforts are consistent with, or exceed, the agency’s statutory authority, how evolving
scientific understanding informs CAA decisionmaking, and potential tradeoffs between public scientific understanding informs CAA decisionmaking, and potential tradeoffs between public
health benefits and compliance costs. Some Members of Congress have also raised concerns health benefits and compliance costs. Some Members of Congress have also raised concerns
about distributional impacts—for example, whether CAA permitting accounts for potential about distributional impacts—for example, whether CAA permitting accounts for potential
disproportionate impacts on air quality in communities located closer to sources of emissions, and disproportionate impacts on air quality in communities located closer to sources of emissions, and
relatedly, whether CAA standard-setting accounts for greater health risks among vulnerable relatedly, whether CAA standard-setting accounts for greater health risks among vulnerable
individuals (e.g., children, pregnant women, the elderly, and persons with preexisting health individuals (e.g., children, pregnant women, the elderly, and persons with preexisting health
conditions). conditions).
Historical Context: Congressional Oversight of EPA’s CAA Rules
Over the past decade, Congress has deliberated on EPA’s authority to promulgate or implement Over the past decade, Congress has deliberated on EPA’s authority to promulgate or implement
new emission control requirements under the CAA. Often under court order, the Obama new emission control requirements under the CAA. Often under court order, the Obama
Administration’s EPA used authorities Congress gave EPA in the CAA amendments of 1970, Administration’s EPA used authorities Congress gave EPA in the CAA amendments of 1970,
1977, and 1990 to address long-standing issues posed by emissions from various sources. During 1977, and 1990 to address long-standing issues posed by emissions from various sources. During
~~that time, EPA’s regulations on greenhouse gas emissions from both mobile and stationary~~
~~sources and on a variety of emissions from electric power plants were of particular interest to~~
~~Congress, as were the agency’s efforts to revise the ozone and particulate matter NAAQS. Some~~

14 haps/petitions-add-1-bp-npb-clean-air-act-list-hazardous-air-pollutants. 15 For discussion of key legal decisions on NSR, see CRS Report R43699, For discussion of key legal decisions on NSR, see CRS Report R43699, Key Historical Court Decisions Shaping
EPA’s Program Under the Clean Air Act, by Linda Tsang. , by Linda Tsang.
1516 42 U.S.C. §7661a and 40 CFR §70.3. Permit applicability depends on the type of air pollutant, whether the source is 42 U.S.C. §7661a and 40 CFR §70.3. Permit applicability depends on the type of air pollutant, whether the source is
located in a nonattainment area, and other criteria. For example, some nonmajor sources of hazardous air pollutants, located in a nonattainment area, and other criteria. For example, some nonmajor sources of hazardous air pollutants,
such as hazardous waste such as hazardous waste ~~combusters~~combustors, may be subject to operating permits. Regardless of size, some sources subject to , may be subject to operating permits. Regardless of size, some sources subject to
the CAA Acid Rain requirements as well as certain solid waste incineration units may be subject to operating permits. the CAA Acid Rain requirements as well as certain solid waste incineration units may be subject to operating permits.
In nonattainment areas, the permit requirements include sources that emit as little as 50, 25, or 10 tons per year of In nonattainment areas, the permit requirements include sources that emit as little as 50, 25, or 10 tons per year of
VOCs, depending on the severity of the region’s ozone nonattainment status (serious, severe, or extreme). See also VOCs, depending on the severity of the region’s ozone nonattainment status (serious, severe, or extreme). See also
EPA, “Who Has to Obtain a Title V Permit?” https://www.epa.gov/title-v-operating-permits/who-has-obtain-title-v-EPA, “Who Has to Obtain a Title V Permit?” https://www.epa.gov/title-v-operating-permits/who-has-obtain-title-v-
permit. permit.
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that time, EPA’s regulations on greenhouse gas emissions from both mobile and stationary sources and on a variety of emissions from electric power plants were of particular interest to Congress, as were the agency’s efforts to revise the ozone and particulate matter NAAQS. Some Members of Congress raised concerns that some of EPA’s regulatory activities exceeded the Members of Congress raised concerns that some of EPA’s regulatory activities exceeded the
authority that Congress had provided through the CAA, that the agency ignored or authority that Congress had provided through the CAA, that the agency ignored or
underestimated the costs and economic impacts, and that EPA overestimated the benefits of underestimated the costs and economic impacts, and that EPA overestimated the benefits of
proposed and promulgated rules. Other Members of Congress disagreed that EPA exceeded its proposed and promulgated rules. Other Members of Congress disagreed that EPA exceeded its
CAA authority, concluding that the agency had a statutory obligation to take action on significant CAA authority, concluding that the agency had a statutory obligation to take action on significant
air pollution issues, such as limiting mercury emissions from power plants, and emphasized the air pollution issues, such as limiting mercury emissions from power plants, and emphasized the
health and environmental benefits of CAA regulations. health and environmental benefits of CAA regulations.
Deliberations on air pollution issues continued in the 115th and 116th Congresses through Deliberations on air pollution issues continued in the 115th and 116th Congresses through
oversight hearings and the introduction of some CAA-related bills. At the same time, the Trump oversight hearings and the introduction of some CAA-related bills. At the same time, the Trump
Administration reviewed many CAA regulations. The CAA mandated some of these reviews, Administration reviewed many CAA regulations. The CAA mandated some of these reviews,
such as the NAAQS reviews and residual risk and technology reviews of hazardous air pollutant such as the NAAQS reviews and residual risk and technology reviews of hazardous air pollutant
standards. Judicial actions, such as the remand of a 2016 rule addressing interstate transport of standards. Judicial actions, such as the remand of a 2016 rule addressing interstate transport of
ground-level ozone, prompted other reviews.ground-level ozone, prompted other reviews.1617 The Trump Administration’s regulatory reform The Trump Administration’s regulatory reform
initiative also led EPA to evaluate existing regulations and some of the accompanying benefit-cost initiative also led EPA to evaluate existing regulations and some of the accompanying benefit-cost
analyses, and to identify those regulations that should be considered for replacement, repeal, or analyses, and to identify those regulations that should be considered for replacement, repeal, or
modification.modification.1718 Examples of rules evaluated under this initiative include those for NSR and the Examples of rules evaluated under this initiative include those for NSR and the
EPA findings from 2000, 2012, and 2016 that limits on hazardous air pollutants from coal- and EPA findings from 2000, 2012, and 2016 that limits on hazardous air pollutants from coal- and
oil-fired power plants are “appropriate and necessary” under CAA Section 112(n)(1). oil-fired power plants are “appropriate and necessary” under CAA Section 112(n)(1).
EPA’s reviews resulted in some regulatory revisions. Some Members of Congress and EPA’s reviews resulted in some regulatory revisions. Some Members of Congress and
stakeholders disagreed with EPA’s rationale—e.g., statutory interpretations and revised benefit-stakeholders disagreed with EPA’s rationale—e.g., statutory interpretations and revised benefit-
cost analyses—for various regulatory decisions and maintained that EPA’s decisions would cost analyses—for various regulatory decisions and maintained that EPA’s decisions would
worsen air quality.worsen air quality.1819 Other Members of Congress and stakeholders agreed with EPA’s revised Other Members of Congress and stakeholders agreed with EPA’s revised
statutory interpretations and updated accounting of benefits and costs.statutory interpretations and updated accounting of benefits and costs.1920
Legislative Proposals in the 116th Congress
At least 47 CAA-related bills were introduced in the 116th Congress. Many of the bills addressed At least 47 CAA-related bills were introduced in the 116th Congress. Many of the bills addressed
either renewable fuel standards or hazardous air emissions. For example, some bills would have either renewable fuel standards or hazardous air emissions. For example, some bills would have
~~revised CAA provisions for renewable fuel standards, and others would have authorized EPA to~~
~~take various actions with respect to hazardous air pollutants. Additional proposals would have~~
~~modified CAA permitting provisions: some would have modified NSR provisions, and others~~

1617 On September 13, 2019, the U.S. Court of Appeals for the District of Columbia Circuit remanded EPA’s 2016 Cross- On September 13, 2019, the U.S. Court of Appeals for the District of Columbia Circuit remanded EPA’s 2016 Cross-
State Air Pollution Rule Update in State Air Pollution Rule Update in Wisconsin v. EPA. For more information, see EPA, “Revised Cross-State Air . For more information, see EPA, “Revised Cross-State Air
Pollution Rule Update,” https://www.epa.gov/csapr/revised-cross-state-air-pollution-rule-update. Pollution Rule Update,” https://www.epa.gov/csapr/revised-cross-state-air-pollution-rule-update.
1718 Executive Order 13777 of February 24, 2017, “Enforcing the Regulatory Reform Agenda,” 82 Executive Order 13777 of February 24, 2017, “Enforcing the Regulatory Reform Agenda,” 82 Federal
Register 12285, March 1, 2017, https://www.federalregister.gov/documents/2017/03/01/2017-04107/enforcing-the- 12285, March 1, 2017, https://www.federalregister.gov/documents/2017/03/01/2017-04107/enforcing-the-
regulatory-reform-agenda. In addition, E.O. 13771 directed agencies, among other actions, to eliminate two regulations regulatory-reform-agenda. In addition, E.O. 13771 directed agencies, among other actions, to eliminate two regulations
for each new regulatory action. Executive Order 13771, “Reducing Regulation and Controlling Regulatory Costs,” 82 for each new regulatory action. Executive Order 13771, “Reducing Regulation and Controlling Regulatory Costs,” 82
Federal Register 9339, January 30, 2017, https://www.federalregister.gov/documents/2017/02/03/2017-02451/ 9339, January 30, 2017, https://www.federalregister.gov/documents/2017/02/03/2017-02451/
reducing-regulation-and-controlling-regulatory-costs. E.O. 13771 and E.O. 13777 were revoked by Executive Order reducing-regulation-and-controlling-regulatory-costs. E.O. 13771 and E.O. 13777 were revoked by Executive Order
13992 of January 20, 2021, “Revocation of Certain Executive Orders Concerning Federal Regulation,” 86 13992 of January 20, 2021, “Revocation of Certain Executive Orders Concerning Federal Regulation,” 86 Federal
Register 7049, January 25, 2021, https://www.federalregister.gov/documents/2021/01/25/2021-01767/revocation-of- 7049, January 25, 2021, https://www.federalregister.gov/documents/2021/01/25/2021-01767/revocation-of-
certain-executive-orders-concerning-federal-regulation. certain-executive-orders-concerning-federal-regulation.
1819 For example, see Senator Tom Carper, For example, see Senator Tom Carper, A Pandemic of Pollution, U.S. Senate Environment and Public Works , U.S. Senate Environment and Public Works
Committee, Staff Report, May 2020, https://www.epw.senate.gov/public/index.cfm/2020/5/carper-releases-new-staff-Committee, Staff Report, May 2020, https://www.epw.senate.gov/public/index.cfm/2020/5/carper-releases-new-staff-
report-on-epa-s-pandemic-of-pollution. report-on-epa-s-pandemic-of-pollution.
1920 For example, see quotes from Members of Congress reported in EPA, “EPA Finalizes MATS Supplemental Cost For example, see quotes from Members of Congress reported in EPA, “EPA Finalizes MATS Supplemental Cost
Finding and ‘Risk and Technology Review,’” press release, April 16, 2020, https://www.epa.gov/newsreleases/epa-Finding and ‘Risk and Technology Review,’” press release, April 16, 2020, https://www.epa.gov/newsreleases/epa-
finalizes-mats-supplemental-cost-finding-and-risk-and-technology-review. finalizes-mats-supplemental-cost-finding-and-risk-and-technology-review.
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revised CAA provisions for renewable fuel standards, and others would have authorized EPA to take various actions with respect to hazardous air pollutants. Additional proposals would have modified CAA permitting provisions: some would have modified NSR provisions, and others would have restricted issuance of CAA operating permits for new sources based on would have restricted issuance of CAA operating permits for new sources based on
environmental justice environmental justice ~~considerations20~~considerations21 among multiple other criteria. among multiple other criteria.
Two additional air quality topics of interest in the 116th Congress were (1) wildfire smoke and (2) Two additional air quality topics of interest in the 116th Congress were (1) wildfire smoke and (2)
potential interactions between air pollution and the COVID-19 pandemic. The 116th Congress potential interactions between air pollution and the COVID-19 pandemic. The 116th Congress
considered options for federal support and assistance to address wildfires and introduced considered options for federal support and assistance to address wildfires and introduced
legislation centered on wildfire smoke.legislation centered on wildfire smoke.2122 For example, S. 1812 and H.R. 4924 would have For example, S. 1812 and H.R. 4924 would have
authorized EPA to research and mitigate the impacts of smoke emissions from wildfires. authorized EPA to research and mitigate the impacts of smoke emissions from wildfires.
Some Members of Congress raised concerns about whether poor air quality makes individuals Some Members of Congress raised concerns about whether poor air quality makes individuals
more vulnerable to COVID-19. For many years, scientific studies found links between air more vulnerable to COVID-19. For many years, scientific studies found links between air
pollution, illness, and premature mortality.pollution, illness, and premature mortality.2223 For example, research has linked exposure to fine For example, research has linked exposure to fine
particles with a range of health effects, including aggravated asthma, chronic bronchitis, and particles with a range of health effects, including aggravated asthma, chronic bronchitis, and
increased premature mortality. More recently, researchers have begun to examine whether there is increased premature mortality. More recently, researchers have begun to examine whether there is
a link between long-term exposure to fine particles and COVID-19 mortality.a link between long-term exposure to fine particles and COVID-19 mortality.2324
Air Pollution Issues in the 117th Congress
Congress may continue to debate questions about air quality and emissions control through its Congress may continue to debate questions about air quality and emissions control through its
EPA oversight or legislation. Congressional oversight also may consider how the Biden EPA oversight or legislation. Congressional oversight also may consider how the Biden
Administration could shape CAA implementation through various administrative tools, such as Administration could shape CAA implementation through various administrative tools, such as
executive orders and policy memoranda. In particular, the Biden Administration has directed executive orders and policy memoranda. In particular, the Biden Administration has directed
federal agencies to review regulations and other agency actions issued by the Trump federal agencies to review regulations and other agency actions issued by the Trump
Administration, and to consider taking actions based on the review. For example, a White House Administration, and to consider taking actions based on the review. For example, a White House
memorandum directed EPA and other agencies to, among other things, consider postponing for 60 memorandum directed EPA and other agencies to, among other things, consider postponing for 60
days (from January 20, 2021) the effective dates of regulations that had been published in the days (from January 20, 2021) the effective dates of regulations that had been published in the
Federal Register but had not yet taken effect. but had not yet taken effect.2425 A second example is Executive Order (E.O.) A second example is Executive Order (E.O.)
13990.13990.2526 E.O. 13990 requires federal agencies to review “all existing regulations, orders, E.O. 13990 requires federal agencies to review “all existing regulations, orders,
guidance documents, policies, and any other similar agency actions” taken during the Trump guidance documents, policies, and any other similar agency actions” taken during the Trump
Administration and to consider “suspending, revising, or rescinding” agency actions that are Administration and to consider “suspending, revising, or rescinding” agency actions that are
deemed inconsistent with the order’s stated policy concerning protection of public health and the deemed inconsistent with the order’s stated policy concerning protection of public health and the
environment and addressing climate change.environment and addressing climate change.2627 E.O. 13990 also specifies timelines for agency E.O. 13990 also specifies timelines for agency
~~heads to consider taking action—suspend, revise, or rescind—on certain rulemakings through a~~
~~notice-and-comment proposed rulemaking. One of these rules is EPA’s 2020 review of the~~

20 21 For more on environmental justice, see CRS In Focus IF10529, For more on environmental justice, see CRS In Focus IF10529, Role of the U.S. Environmental Protection Agency in
Environmental Justice, by David M. Bearden and Angela C. Jones. , by David M. Bearden and Angela C. Jones.
2122 CRS In Focus IF10732, CRS In Focus IF10732, Federal Assistance for Wildfire Response and Recovery, by Katie Hoover. , by Katie Hoover.
2223 For example, see EPA, For example, see EPA, Integrated Science Assessment (ISA) for Particulate Matter, December 2019, , December 2019,
https://cfpub.epa.gov/ncea/isa/recordisplay.cfm?deid=347534. https://cfpub.epa.gov/ncea/isa/recordisplay.cfm?deid=347534.
2324 X. Wu et al., “Air Pollution and COVID-19 Mortality in the United States: Strengths and Limitations of an X. Wu et al., “Air Pollution and COVID-19 Mortality in the United States: Strengths and Limitations of an
Ecological Regression Analysis,” Ecological Regression Analysis,” Science Advances, vol. 6, no. 45 (November 4, 2020), , vol. 6, no. 45 (November 4, 2020),
https://advances.sciencemag.org/content/6/45/eabd4049. https://advances.sciencemag.org/content/6/45/eabd4049.
2425 Presidential Actions, Memorandum for the Heads of Executive Departments and Agencies, “Regulatory Freeze Presidential Actions, Memorandum for the Heads of Executive Departments and Agencies, “Regulatory Freeze
Pending Review,” January 20, 2021, https://www.whitehouse.gov/briefing-room/presidential-actions/2021/01/20/Pending Review,” January 20, 2021, https://www.whitehouse.gov/briefing-room/presidential-actions/2021/01/20/
regulatory-freeze-pending-review/. See also CRS Legal Sidebar LSB10566, regulatory-freeze-pending-review/. See also CRS Legal Sidebar LSB10566, Responses to Midnight Rulemaking: Legal
Issues, by Daniel J. Sheffner and Kate R. Bowers. , by Daniel J. Sheffner and Kate R. Bowers.
2526 Executive Order 13990 of January 20, 2021, “Protecting Public Health and the Environment and Restoring Science Executive Order 13990 of January 20, 2021, “Protecting Public Health and the Environment and Restoring Science
to Tackle the Climate Crisis,” 86to Tackle the Climate Crisis,” 86 Federal Register 7037, January 25, 2021. 7037, January 25, 2021.
2627 The policy is presented in E.O. 13990, Section 1. The policy is presented in E.O. 13990, Section 1.
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heads to consider taking action—suspend, revise, or rescind—on certain rulemakings through a notice-and-comment proposed rulemaking. One of these rules is EPA’s 2020 review of the benefits and costs of reducing mercury and other hazardous air pollutants from coal- and oil-fired benefits and costs of reducing mercury and other hazardous air pollutants from coal- and oil-fired
power plants.power plants.~~27 EPA is to consider taking action on this rule by August 2021.~~28 28
Congress may consider legislation to address continued concerns about air pollution and Congress may consider legislation to address continued concerns about air pollution and
disagreements about EPA’s CAA authority. Recent Administrations have interpreted CAA disagreements about EPA’s CAA authority. Recent Administrations have interpreted CAA
authority in different, and sometimes conflicting, ways. Historically, many of EPA’s CAA authority in different, and sometimes conflicting, ways. Historically, many of EPA’s CAA
regulations have been challenged in court, both by industry and by public health and regulations have been challenged in court, both by industry and by public health and
environmental groups, with various states supporting each side. Industry stakeholders have environmental groups, with various states supporting each side. Industry stakeholders have
maintained that under some Administrations, EPA has overreached its CAA authority. maintained that under some Administrations, EPA has overreached its CAA authority.
Environmental and public health groups have often asserted that EPA standards are not Environmental and public health groups have often asserted that EPA standards are not
sufficiently protective of public health or do not meet statutory requirements, or that the agency sufficiently protective of public health or do not meet statutory requirements, or that the agency
has disregarded its science advisors. has disregarded its science advisors.
The remainder of this report discusses CAA topics that will likely garner attention in the 117th The remainder of this report discusses CAA topics that will likely garner attention in the 117th
Congress. Congress.
Congressional Review
Congress may also use the Congressional Review Act (CRA) to review some rules that were Congress may also use the Congressional Review Act (CRA) to review some rules that were
promulgated by the Trump Administration and submitted late in the 116th Congress.29 The most promulgated by the Trump Administration and submitted late in the 116th Congress.29 The most
likely timing for using the CRA is at the outset of the 117th Congress. likely timing for using the CRA is at the outset of the 117th Congress.
The CRA provides one special legislative mechanism through which Congress may review and The CRA provides one special legislative mechanism through which Congress may review and
disapprove of an agency rule through a joint resolution, which cannot be filibustered in the disapprove of an agency rule through a joint resolution, which cannot be filibustered in the
Senate, provided it meets certain conditions.30 Under the CRA, if Congress passes a joint Senate, provided it meets certain conditions.30 Under the CRA, if Congress passes a joint
resolution disapproving a rule and the resolution becomes law, the rule cannot take effect or resolution disapproving a rule and the resolution becomes law, the rule cannot take effect or
continue in effect.31 The agency may not reissue either that rule or any substantially similar one, continue in effect.31 The agency may not reissue either that rule or any substantially similar one,
except under authority of a subsequently enacted law. For a CRA resolution to become law, except under authority of a subsequently enacted law. For a CRA resolution to become law,
however, the President must sign it or allow it to become law without signature, or Congress however, the President must sign it or allow it to become law without signature, or Congress
overrides a presidential veto. overrides a presidential veto.
The CRA specifies deadlines that determine which final rules could be considered using this The CRA specifies deadlines that determine which final rules could be considered using this
legislative mechanism. If Congress adjourns before the period authorized by the CRA to legislative mechanism. If Congress adjourns before the period authorized by the CRA to
introduce and act on a disapproval resolution for a rule, the CRA’s “lookback” provision allows introduce and act on a disapproval resolution for a rule, the CRA’s “lookback” provision allows
the next Congress to consider doing so. The lookback provision is intended to ensure that the next Congress to consider doing so. The lookback provision is intended to ensure that
Congress will have the full periods contemplated by the act to disapprove a rule regardless of Congress will have the full periods contemplated by the act to disapprove a rule regardless of
when it is received.32 Under Section 801(d) of the CRA, final rules submitted to Congress on or when it is received.32 Under Section 801(d) of the CRA, final rules submitted to Congress on or
~~after the 60th meeting day before adjournment in either the Senate or the House are subject to~~

2728 EPA, “National Emission Standards for Hazardous Air Pollutants: Coal- and Oil-Fired Electric Utility Steam EPA, “National Emission Standards for Hazardous Air Pollutants: Coal- and Oil-Fired Electric Utility Steam
Generating Units—Subcategory of Certain Existing Electric Utility Steam Generating Units Firing Eastern Bituminous Generating Units—Subcategory of Certain Existing Electric Utility Steam Generating Units Firing Eastern Bituminous
Coal Refuse for Emissions of Acid Gas Hazardous Air Pollutants,” 85Coal Refuse for Emissions of Acid Gas Hazardous Air Pollutants,” 85 Federal Register 20838, April 15, 2020. 20838, April 15, 2020.
28 E.O. E.O. 13990, Section 2(iv) directed EPA to consider taking action on this rule by August 2021. As of this report’s publication date, EPA has not issued a rulemaking action related to this rule.~~13990, Section 2(iv). The 2020 rule is discussed later in this report; see~~ ~~“Mercury from Power Plants: EPA’s~~
~~Consideration of Co-Benefits.~~”
29 Title II, Subtitle E, P.L. 104-121, 5 U.S.C. §§801-808. 29 Title II, Subtitle E, P.L. 104-121, 5 U.S.C. §§801-808.
30 CRS Report R43992, 30 CRS Report R43992, The Congressional Review Act (CRA): Frequently Asked Questions, by Maeve P. Carey and , by Maeve P. Carey and
Christopher M. Davis. For questions about the CRA, congressional clients may contact Maeve Carey, Specialist in Christopher M. Davis. For questions about the CRA, congressional clients may contact Maeve Carey, Specialist in
Government Organization and Management. Government Organization and Management.
31 The CRA adopts a broad definition of 31 The CRA adopts a broad definition of rule; for more information, see CRS Report R43992, ; for more information, see CRS Report R43992, The Congressional
Review Act (CRA): Frequently Asked Questions, by Maeve P. Carey and Christopher M. Davis. , by Maeve P. Carey and Christopher M. Davis.
32 CRS In Focus IF10023, 32 CRS In Focus IF10023, The Congressional Review Act (CRA), by Maeve P. Carey and Christopher M. Davis. , by Maeve P. Carey and Christopher M. Davis.
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after the 60th meeting day before adjournment in either the Senate or the House are subject to renewed periods for congressional review.33 That is, for regulations submitted to the 116th renewed periods for congressional review.33 That is, for regulations submitted to the 116th
Congress within 60 meeting days before adjournment in either chamber, the 117th Congress may Congress within 60 meeting days before adjournment in either chamber, the 117th Congress may
consider a joint resolution of disapproval of such regulations using the special CRA procedures. consider a joint resolution of disapproval of such regulations using the special CRA procedures.
CRS unofficially estimates that final rules received during the 116th Congress on or after August CRS unofficially estimates that final rules received during the 116th Congress on or after August
21, 2020, are potentially eligible for additional periods of CRA review in the 117th Congress. The 21, 2020, are potentially eligible for additional periods of CRA review in the 117th Congress. The
Senate and House Parliamentarians are the sole definitive arbiters of the CRA mechanism, Senate and House Parliamentarians are the sole definitive arbiters of the CRA mechanism,
however, and should be consulted for guidance on any specific question. however, and should be consulted for guidance on any specific question.
EPA has finalized numerous rules that may be considered under the CRA, and at least 90 of these EPA has finalized numerous rules that may be considered under the CRA, and at least 90 of these
rules were promulgated in the last six months of the Trump Administration. The vast majority of rules were promulgated in the last six months of the Trump Administration. The vast majority of
the rules promulgated in the last six months of the Trump Administration were actions on state the rules promulgated in the last six months of the Trump Administration were actions on state
implementation plans, based on EPA’s review of the plans. Of the remaining CAA rules implementation plans, based on EPA’s review of the plans. Of the remaining CAA rules
promulgated during this period, the following four are discussed in greater detail in this report: promulgated during this period, the following four are discussed in greater detail in this report:
1. Air Quality Standards: EPA, “Review of the National Ambient Air Quality 1. Air Quality Standards: EPA, “Review of the National Ambient Air Quality
Standards for Ozone,” final rule, 85 Standards for Ozone,” final rule, 85 Federal Register 87256, December 31, 2020. 87256, December 31, 2020.
(See (See “Particulate Matter and Ozone NAAQS Reviews.”) ”)
2. Air Quality Standards: EPA, “Review of the National Ambient Air Quality 2. Air Quality Standards: EPA, “Review of the National Ambient Air Quality
Standards for Particulate Matter,” final rule, 85 Standards for Particulate Matter,” final rule, 85 Federal Register 82684, 82684,
December 18, 2020. (See December 18, 2020. (See “Particulate Matter and Ozone NAAQS Reviews.”) ”)
3. Preconstruction Permits: EPA, “Prevention of Significant Deterioration (PSD) 3. Preconstruction Permits: EPA, “Prevention of Significant Deterioration (PSD)
and Nonattainment New Source Review (NNSR): Project Emissions and Nonattainment New Source Review (NNSR): Project Emissions
Accounting,” 85Accounting,” 85 Federal Register 74890, November 24, 2020. (See 74890, November 24, 2020. (See “New Source
Review Permits.”) ”)
4. Hazardous Air Pollutants: EPA, “Reclassification of Major Sources as Area 4. Hazardous Air Pollutants: EPA, “Reclassification of Major Sources as Area
Sources Under Section 112 of the Clean Air Act,” final rule, 85 Sources Under Section 112 of the Clean Air Act,” final rule, 85 Federal Register
73854, November 19, 2020. (See 73854, November 19, 2020. (See “Source Classification: 2018 EPA Withdrawal
of “Once In, Always In” Policy.”) ”)
~~In addition to considering rules pursuant to the CRA, the 117th Congress may also address rules~~
While the 117th Congress did not consider these four rules pursuant to the CRA, Congress may address them through other types of legislation or through the appropriations process. The courts will continue through other types of legislation or through the appropriations process. The courts will continue
to play an important role, and the 117th Congress and EPA itself may act to make important to play an important role, and the 117th Congress and EPA itself may act to make important
~~revisions to CAA regulations.~~
revisions to CAA regulations. Particulate Matter and Ozone NAAQS Reviews In December 2020, EPA completed its statutorily mandated reviews of the particulate matter NAAQS and the ozone NAAQS. EPA finalized two rules, one to retain the current particulate
33 §801(d) of the CRA provides that, if a final rule is submitted to Congress less than 60 session days in the Senate or 33 §801(d) of the CRA provides that, if a final rule is submitted to Congress less than 60 session days in the Senate or
less than 60 legislative days in the House of Representatives before Congress adjourns a session less than 60 legislative days in the House of Representatives before Congress adjourns a session sine die, a new period , a new period
for congressional review of that rule becomes available in the next session of Congress. For more information about for congressional review of that rule becomes available in the next session of Congress. For more information about
this “lookback” period and other CRA elements, see CRS Report R43992, this “lookback” period and other CRA elements, see CRS Report R43992, The Congressional Review Act (CRA):
Frequently Asked Questions, by Maeve P. Carey and Christopher M. Davis. , by Maeve P. Carey and Christopher M. Davis.
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~~Particulate Matter and Ozone NAAQS Reviews~~
~~In December 2020, EPA completed its statutorily mandated reviews of the particulate matter~~
~~NAAQS and the ozone NAAQS. EPA finalized two rules, one to retain the current~~ matter standards34 and another to retain the current ozone standards.35 In 2021, EPA announced that it would reconsider the 2020 decision to retain the particulate particulate
matter matter ~~standards34 and another~~standards36 and the 2020 decision to retain the to retain the ~~current~~ ozone standards.ozone standards.35
37 Stakeholder opinion regarding whether EPA should revise the particulate matter and ozone Stakeholder opinion regarding whether EPA should revise the particulate matter and ozone
standards varies. For example, some Members of Congress concurred with EPA’s rulemaking to standards varies. For example, some Members of Congress concurred with EPA’s rulemaking to
retain particulate matter standards, describing the current standards as “among the strictest retain particulate matter standards, describing the current standards as “among the strictest
safeguards” globally and observing that U.S. air quality has improved over time.safeguards” globally and observing that U.S. air quality has improved over time.3638 Other Other
Members of Congress have urged EPA to tighten the particulate matter standards. For example, in Members of Congress have urged EPA to tighten the particulate matter standards. For example, in
a letter to the EPA Administrator dated June 29, 2020, some Members noted concerns about how a letter to the EPA Administrator dated June 29, 2020, some Members noted concerns about how
air quality may disproportionately affect certain communities—such as low-income communities, air quality may disproportionately affect certain communities—such as low-income communities,
communities of color, and Tribal and indigenous communities—and potentially interact with communities of color, and Tribal and indigenous communities—and potentially interact with
COVID-19.COVID-19.3739
NAAQS Review Process
The NAAQS review process has evolved over time, with multiple Administrations introducing The NAAQS review process has evolved over time, with multiple Administrations introducing
procedural modifications intended to streamline the process, improve transparency, or strengthen procedural modifications intended to streamline the process, improve transparency, or strengthen
the scientific basis. Beyond the CAA requirements discussed earlier in this report, the procedural the scientific basis. Beyond the CAA requirements discussed earlier in this report, the procedural
aspects of the NAAQS review are generally at the discretion of the EPA Administrator.aspects of the NAAQS review are generally at the discretion of the EPA Administrator.~~38 Most~~
~~recently, the~~ 40 The Trump Administration has sought to streamline NAAQS reviews by restructuring the Trump Administration has sought to streamline NAAQS reviews by restructuring the
review process.review process.3941 For example, EPA structured the most For example, EPA structured the most ~~recent~~recently completed ozone review to last roughly two- ozone review to last roughly two-
and-a-half years. The previous ozone review lasted about seven years. EPA compressed the ozone and-a-half years. The previous ozone review lasted about seven years. EPA compressed the ozone
NAAQS review schedule by releasing two draft analyses—the Integrated Science Assessment NAAQS review schedule by releasing two draft analyses—the Integrated Science Assessment
and the Policy Assessment—nearly concurrently for simultaneous review by CASAC. This and the Policy Assessment—nearly concurrently for simultaneous review by CASAC. This
approach differed from previously completed reviews in which EPA considered approach differed from previously completed reviews in which EPA considered ~~CASAC input~~
~~and public comments on the Integrated Science Assessment as EPA developed the Policy~~
~~Assessment.~~

34 EPA, “Review of the National Ambient Air Quality Standards for Particulate Matter,” Final action, 85 34 EPA, “Review of the National Ambient Air Quality Standards for Particulate Matter,” Final action, 85 Federal
Register 82684, December 18, 2020. EPA completed its prior review of the particulate matter NAAQS in late 2012 and 82684, December 18, 2020. EPA completed its prior review of the particulate matter NAAQS in late 2012 and
promulgated revisions to strengthen the standards. EPA published the final rule in the promulgated revisions to strengthen the standards. EPA published the final rule in the Federal Register in 2013; see in 2013; see
EPA, “National Ambient Air Quality Standards for Particulate Matter, Final Rule,” 78EPA, “National Ambient Air Quality Standards for Particulate Matter, Final Rule,” 78 Federal Register 3086, January 3086, January
15, 2013. 15, 2013.
35 EPA, “Review of the Ozone National Ambient Air Quality Standards,” Final action, 85 35 EPA, “Review of the Ozone National Ambient Air Quality Standards,” Final action, 85 Federal Register 87256, 87256,
December 31, 2020. EPA completed its prior review of the ozone NAAQS in 2015, at which time it strengthened the December 31, 2020. EPA completed its prior review of the ozone NAAQS in 2015, at which time it strengthened the
ozone standards. See EPA, “National Ambient Air Quality Standards for Ozone, Final Rule,” 80 ozone standards. See EPA, “National Ambient Air Quality Standards for Ozone, Final Rule,” 80 Federal Register
65292, October 26, 2015. 65292, October 26, 2015.
36 36 EPA, “EPA to Reexamine Health Standards for Harmful Soot that Previous Administration Left Unchanged,” press release, June 10, 2021, https://www.epa.gov/newsreleases/epa-reexamine-health-standards-harmful-soot-previous-administration-left-unchanged. 37 EPA, EPA to Reconsider Previous Administration’s Decision to Retain 2015 Ozone Standards, https://www.epa.gov/ground-level-ozone-pollution/epa-reconsider-previous-administrations-decision-retain-2015-ozone. 38 EPA, “What They Are Saying: EPA Proposes to Retain NAAQS for Particulate Matter,” press release, April 14, EPA, “What They Are Saying: EPA Proposes to Retain NAAQS for Particulate Matter,” press release, April 14,
2020, https://www.epa.gov/newsreleases/what-they-are-saying-epa-proposes-retain-naaqs-particulate-matter. 2020, https://www.epa.gov/newsreleases/what-they-are-saying-epa-proposes-retain-naaqs-particulate-matter.
3739 Some Members of Congress stated that such communities are disproportionately affected by particulate matter air Some Members of Congress stated that such communities are disproportionately affected by particulate matter air
pollution and that studies show that “Americans living in areas with higher levels of particulate matter pollution are pollution and that studies show that “Americans living in areas with higher levels of particulate matter pollution are
more likely to die from COVID-19 than those living in areas with cleaner air.” Letter from Thomas R. Carper, U.S. more likely to die from COVID-19 than those living in areas with cleaner air.” Letter from Thomas R. Carper, U.S.
Senator, et al. to Andrew Wheeler, EPA Administrator, June 29, 2020. Senator, et al. to Andrew Wheeler, EPA Administrator, June 29, 2020.
3840 For summary of relevant statutory requirements, see the For summary of relevant statutory requirements, see the “Overview of the Clean Air Act” section of this report. section of this report.
3941 Letter from the Honorable E. Scott Pruitt, EPA Administrator, to EPA Assistant Administrators, May 9, 2018, Letter from the Honorable E. Scott Pruitt, EPA Administrator, to EPA Assistant Administrators, May 9, 2018,
https://www.epa.gov/criteria-air-pollutants/back-basics-process-reviewing-national-ambient-air-quality-standards. https://www.epa.gov/criteria-air-pollutants/back-basics-process-reviewing-national-ambient-air-quality-standards.
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CASAC input and public comments on the Integrated Science Assessment as EPA developed the Policy Assessment. Historically, pollutant-specific scientific review panels have advised agency staff during their Historically, pollutant-specific scientific review panels have advised agency staff during their
reviews. EPA took a different approach in the multiyear NAAQS reviews it completed in 2020.reviews. EPA took a different approach in the multiyear NAAQS reviews it completed in 2020.4042
For example, in 2018, EPA disbanded the CASAC Particulate Matter Review Panel formed in For example, in 2018, EPA disbanded the CASAC Particulate Matter Review Panel formed in
2015. The agency did not convene an ozone panel to review the 2015 ozone NAAQS. Instead, 2015. The agency did not convene an ozone panel to review the 2015 ozone NAAQS. Instead,
EPA directed the seven-member CASAC to assist EPA with reviews for the particulate matter and EPA directed the seven-member CASAC to assist EPA with reviews for the particulate matter and
ozone NAAQS on an expedited timeline. CASAC and others have expressed concerns about the ozone NAAQS on an expedited timeline. CASAC and others have expressed concerns about the
lack of pollutant-specific panels. In 2019, CASAC recommended EPA either reappoint the lack of pollutant-specific panels. In 2019, CASAC recommended EPA either reappoint the
CASAC particulate matter panel or appoint a new panel with similar expertise. CASAC stated CASAC particulate matter panel or appoint a new panel with similar expertise. CASAC stated
that the “breadth and diversity of evidence to be considered exceeds the expertise of the statutory that the “breadth and diversity of evidence to be considered exceeds the expertise of the statutory
CASAC members.”CASAC members.”4143 EPA subsequently announced the availability of 12 subject matter experts to EPA subsequently announced the availability of 12 subject matter experts to
assist CASAC with technical questions.assist CASAC with technical questions.4244 CASAC continued to urge EPA to “consider restoring a CASAC continued to urge EPA to “consider restoring a
traditional interactive discussion process in which the CASAC can interact directly with external traditional interactive discussion process in which the CASAC can interact directly with external
expert panels, while also keeping the option of obtaining written responses from external experts expert panels, while also keeping the option of obtaining written responses from external experts
to specific questions.”to specific questions.”43
45 In 2021, EPA signaled interest in pollutant-specific review panels, convening a CASAC Particulate Matter Panel to “provide advice through the chartered CASAC on updates to the science and policy assessments supporting the agency’s reconsideration” of the agency’s 2020 decision to retain the particulate matter standards.”46 In its oversight role, Congress may consider if EPA’s In its oversight role, Congress may consider if EPA’s ~~revised~~ approach meets the CAA objectives approach meets the CAA objectives
to review the NAAQS and the science upon which they are based in a timely manner. EPA’s to review the NAAQS and the science upon which they are based in a timely manner. EPA’s
modifications to the NAAQS review process underscore the tension between competing concerns. modifications to the NAAQS review process underscore the tension between competing concerns.
Some stakeholders, interest groups, and Members of Congress have criticized the timeliness of Some stakeholders, interest groups, and Members of Congress have criticized the timeliness of
past NAAQS reviews, noting that delayed reviews contribute to regulatory uncertainty. Others past NAAQS reviews, noting that delayed reviews contribute to regulatory uncertainty. Others
question whether expedited NAAQS decisions are able to reflect the latest science and if the question whether expedited NAAQS decisions are able to reflect the latest science and if the
scientific basis is sufficiently rigorous. scientific basis is sufficiently rigorous.
Wildfire Smoke
Congress may continue to deliberate legislation related to wildfires and smoke management in the Congress may continue to deliberate legislation related to wildfires and smoke management in the
117th Congress. Wildfire smoke is a complex mixture of air pollutants that can temporarily 117th Congress. Wildfire smoke is a complex mixture of air pollutants that can temporarily
degrade air quality and harm human health. The chemical composition of smoke depends on degrade air quality and harm human health. The chemical composition of smoke depends on
~~various factors including burn conditions (e.g., fire temperature), type of biomass burned (e.g.,~~
~~vegetation), and weather-related influences (e.g., wind).44~~
~~Wildfire smoke can temporarily increase ambient levels of particulate matter and other criteria~~
~~pollutants regulated under the CAA.45 These increases may be measured by air monitoring~~
~~stations comprising a national network, which informs determinations about NAAQS compliance.~~

40 42 EPA initiated this particulate matter NAAQS review in December 2014 and initiated this ozone NAAQS review in EPA initiated this particulate matter NAAQS review in December 2014 and initiated this ozone NAAQS review in
May 2018. EPA, “Review of the National Ambient Air Quality Standards for Particulate Matter,” Final action, 85 May 2018. EPA, “Review of the National Ambient Air Quality Standards for Particulate Matter,” Final action, 85
Federal Register 87261, December 18, 2020. 87261, December 18, 2020.
4143 Letter from Dr. Louis Anthony Cox, Jr., Chair, CASAC, to the Honorable Andrew R. Wheeler, EPA Administrator, Letter from Dr. Louis Anthony Cox, Jr., Chair, CASAC, to the Honorable Andrew R. Wheeler, EPA Administrator,
April 11, 2019. April 11, 2019.
4244 EPA, “Administrator Wheeler Announces New CASAC Member, Pool of NAAQS Subject Matter Experts,” press EPA, “Administrator Wheeler Announces New CASAC Member, Pool of NAAQS Subject Matter Experts,” press
release, September 13, 2019, https://www.epa.gov/newsreleases/administrator-wheeler-announces-new-casac-member-release, September 13, 2019, https://www.epa.gov/newsreleases/administrator-wheeler-announces-new-casac-member-
pool-naaqs-subject-matter-experts. pool-naaqs-subject-matter-experts.
4345 Letter from Dr. Louis Anthony Cox, Jr., Chair, CASAC, to the Honorable Andrew R. Wheeler, EPA Administrator, Letter from Dr. Louis Anthony Cox, Jr., Chair, CASAC, to the Honorable Andrew R. Wheeler, EPA Administrator,
February 19, 2020. February 19, 2020.
~~44 EPA, U.S. Forest Service, U.S. Centers for Disease Control and Prevention, and California Air Resources Board,~~
~~California Office of Environmental Health Hazard Assessment, Wildfire Smoke: A Guide for Public Health Officials,~~
~~Revised 2019, https://www.airnow.gov/publications/wildfire-smoke-guide/wildfire-smoke-a-guide-for-public-health-~~
~~officials/.~~
~~45 For more information, see CRS Insight IN11528, Wildfire Smoke: Air Quality Concerns and Management, by Kate~~
~~C. Shouse.~~
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46 EPA, “Request for Nominations of Candidates for the Clean Air Scientific Advisory Committee (CASAC) Particulate Matter (PM) Panel,” 86 Federal Register 33703, June 25, 2021. See also EPA, 2021 CASAC PM Panel, https://casac.epa.gov/ords/sab/f?p=105:14:13752977270736:::14:P14_COMMITTEEON:2021%20CASAC%20PM%20Panel. Congressional Research Service 9 Clean Air Act Issues in the 117th Congress various factors including burn conditions (e.g., fire temperature), type of biomass burned (e.g., vegetation), and weather-related influences (e.g., wind).47 Wildfire smoke can temporarily increase ambient levels of particulate matter and other criteria pollutants regulated under the CAA.48 These increases may be measured by air monitoring stations comprising a national network, which informs determinations about NAAQS compliance. Congress authorized EPA to treat emissions from certain natural events differently than those Congress authorized EPA to treat emissions from certain natural events differently than those
from anthropogenic sources. The CAA allows EPA to exclude air quality data from regulatory from anthropogenic sources. The CAA allows EPA to exclude air quality data from regulatory
decisions if such data were demonstratively influenced by “exceptional events” such as certain decisions if such data were demonstratively influenced by “exceptional events” such as certain
natural events (42 U.S.C. §7619(b)). EPA regulations specify conditions under which states and natural events (42 U.S.C. §7619(b)). EPA regulations specify conditions under which states and
tribes can demonstrate that air quality impacts from wildfires should be excluded from NAAQS tribes can demonstrate that air quality impacts from wildfires should be excluded from NAAQS
compliance determinations.compliance determinations.4649 Such exclusions are neither required nor guaranteed. That is, air Such exclusions are neither required nor guaranteed. That is, air
quality data influenced by exceptional events are not excluded unless a state, tribe, federal land quality data influenced by exceptional events are not excluded unless a state, tribe, federal land
manager, or other federal agency submits a demonstration to EPA and the agency approves the manager, or other federal agency submits a demonstration to EPA and the agency approves the
demonstration.demonstration.4750 EPA’s review may qualitatively weigh the evidence presented in the exceptional EPA’s review may qualitatively weigh the evidence presented in the exceptional
events demonstration “based on its relevance to the Exceptional Events Rule criterion being events demonstration “based on its relevance to the Exceptional Events Rule criterion being
addressed, the degree of certainty, its persuasiveness, and other considerations appropriate to the addressed, the degree of certainty, its persuasiveness, and other considerations appropriate to the
individual pollutant and the nature and type of event.”individual pollutant and the nature and type of event.”4851
Wildfire response strategies rely on air quality monitoring, smoke forecasting, and timely Wildfire response strategies rely on air quality monitoring, smoke forecasting, and timely
communication of air quality conditions and related health risks to the public.communication of air quality conditions and related health risks to the public.4952 Various federal, Various federal,
tribal, state, and local agencies contribute to these tasks.tribal, state, and local agencies contribute to these tasks.5053 To measure ambient air pollutant To measure ambient air pollutant
levels, they rely on established monitors from the national network and deploy temporary levels, they rely on established monitors from the national network and deploy temporary
monitors. Specialists also use computer modeling to estimate pollution levels. In addition, EPA monitors. Specialists also use computer modeling to estimate pollution levels. In addition, EPA
manages AirNow, a multiagency website that reports air quality based on monitoring data manages AirNow, a multiagency website that reports air quality based on monitoring data
received on a regular basis from state, local, and federal agencies.received on a regular basis from state, local, and federal agencies.5154 AirNow compiles the data in 47 EPA, U.S. Forest Service, U.S. Centers for Disease Control and Prevention, and California Air Resources Board, California Office of Environmental Health Hazard Assessment, Wildfire Smoke: A Guide for Public Health Officials, Revised 2019, https://www.airnow.gov/publications/wildfire-smoke-guide/wildfire-smoke-a-guide-for-public-health-officials/. 48 For more information, see CRS Insight IN11528, Wildfire Smoke: Air Quality Concerns and Management, by Kate C. Shouse. 49 ~~AirNow compiles the data in~~
~~a consistent format and displays it through interactive maps, such as the Fire and Smoke Map.52~~
~~The need for real-time air quality information is critical during wildfire events.~~
~~EPA, the U.S. Forest Service, other agencies, and stakeholders are exploring emerging~~
~~technologies to improve air quality monitoring during wildfire events. For example, the AirNow~~
~~Sensor Data Pilot adds air pollution data from “low-cost sensors” to the Fire and Smoke Map.~~
~~Federal agencies caution that such data should be considered supplemental to existing resources,~~
~~given uncertainties about the “precision, accuracy, and reliability” of sensors.53~~

46 For example, states and tribes may submit a demonstration that addresses the technical criterion that “the event For example, states and tribes may submit a demonstration that addresses the technical criterion that “the event
affected air quality in such a way that there exists a clear causal relationship between the specific event and the affected air quality in such a way that there exists a clear causal relationship between the specific event and the
monitored exceedance or violation.” 40 C.F.R. §50.14(c)(3)(iv)(B)-(C). See also EPA, “Treatment of Air Quality Data monitored exceedance or violation.” 40 C.F.R. §50.14(c)(3)(iv)(B)-(C). See also EPA, “Treatment of Air Quality Data
Influenced by Exceptional Events,” https://www.epa.gov/air-quality-analysis/treatment-air-quality-data-influenced-Influenced by Exceptional Events,” https://www.epa.gov/air-quality-analysis/treatment-air-quality-data-influenced-
exceptional-events-homepage-exceptional. exceptional-events-homepage-exceptional.
4750 42 U.S.C. §7619(b)(1). See also 40 C.F.R. §50.14 and EPA, “2016 Revisions to the Exceptional Events Rule: Update 42 U.S.C. §7619(b)(1). See also 40 C.F.R. §50.14 and EPA, “2016 Revisions to the Exceptional Events Rule: Update
to Frequently Asked Questions,” February 2020, https://www.epa.gov/air-quality-analysis/updated-exceptional-events-to Frequently Asked Questions,” February 2020, https://www.epa.gov/air-quality-analysis/updated-exceptional-events-
rule-faqs. rule-faqs.
4851 EPA, “Exceptional Events Guidance: Prescribed Fire on Wildland that May Influence Ozone and Particulate Matter EPA, “Exceptional Events Guidance: Prescribed Fire on Wildland that May Influence Ozone and Particulate Matter
Concentrations,” August 19, 2019, https://www.epa.gov/air-quality-analysis/exceptional-events-guidance-prescribed-Concentrations,” August 19, 2019, https://www.epa.gov/air-quality-analysis/exceptional-events-guidance-prescribed-
fire-wildland-may-influence-ozone-and. fire-wildland-may-influence-ozone-and.
4952 For example, see California Air Resources Board, California Office of Environmental Health Hazard Assessment, For example, see California Air Resources Board, California Office of Environmental Health Hazard Assessment,
EPA, U.S. Centers for Disease Control and Prevention, and U.S. Forest Service, EPA, U.S. Centers for Disease Control and Prevention, and U.S. Forest Service, Wildfire Smoke: A Guide for Public
Health Officials, Revised 2019, https://www.airnow.gov/publications/wildfire-smoke-guide/wildfire-smoke-a-guide-, Revised 2019, https://www.airnow.gov/publications/wildfire-smoke-guide/wildfire-smoke-a-guide-
for-public-health-officials/. Hereinafter, “2019 Wildfire Smoke Guide.” for-public-health-officials/. Hereinafter, “2019 Wildfire Smoke Guide.”
5053 For example, see (1) Interagency Wildland Fire Air Quality Response Program, “Air Resource Advisors,” For example, see (1) Interagency Wildland Fire Air Quality Response Program, “Air Resource Advisors,”
https://sites.google.com/firenet.gov/wfaqrp-external/air-resource-advisors; and (2) AirNow, “Smoke Advisories,” https://sites.google.com/firenet.gov/wfaqrp-external/air-resource-advisors; and (2) AirNow, “Smoke Advisories,”
https://www.airnow.gov/air-quality-and-health/fires/smoke-advisories/. https://www.airnow.gov/air-quality-and-health/fires/smoke-advisories/.
5154 AirNow, About AirNow, https://www.airnow.gov/about-airnow/. AirNow, About AirNow, https://www.airnow.gov/about-airnow/.
~~52 AirNow, Fire and Smoke Map, https://fire.airnow.gov/.~~
~~53 2019 Wildfire Smoke Guide, p. 3.~~
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Congressional Research Service 10 Clean Air Act Issues in the 117th Congress a consistent format and displays it through interactive maps, such as the Fire and Smoke Map.55 The need for real-time air quality information is critical during wildfire events. EPA, the U.S. Forest Service, other agencies, and stakeholders are exploring emerging technologies to improve air quality monitoring during wildfire events. For example, the AirNow Sensor Data Pilot adds air pollution data from “low-cost sensors” to the Fire and Smoke Map. Federal agencies caution that such data should be considered supplemental to existing resources, given uncertainties about the “precision, accuracy, and reliability” of sensors.56 CAA requirements may also factor into forest management and fire prevention strategies, CAA requirements may also factor into forest management and fire prevention strategies,
specifically the use of prescribed fires. Prescribed fires—the deliberate use of fire in specific specifically the use of prescribed fires. Prescribed fires—the deliberate use of fire in specific
areas within prescribed fuel and weather conditions—are one option often considered to reduce areas within prescribed fuel and weather conditions—are one option often considered to reduce
fuel levels (e.g., dead wood) and thereby reduce risk of larger wildfires.fuel levels (e.g., dead wood) and thereby reduce risk of larger wildfires.5457 Various factors Various factors
influence the use of prescribed fires, including available capacity and funding, air quality and influence the use of prescribed fires, including available capacity and funding, air quality and
other health and safety concerns, compliance with air quality requirements, and landscape other health and safety concerns, compliance with air quality requirements, and landscape
conditions and conservation priorities.conditions and conservation priorities.5558 Many states have developed programs to manage and Many states have developed programs to manage and
control smoke from prescribed fires.control smoke from prescribed fires.5659 Smoke management plans seek to minimize smoke Smoke management plans seek to minimize smoke
entering populated areas, prevent public safety hazards, and maintain CAA compliance. entering populated areas, prevent public safety hazards, and maintain CAA compliance.
Notwithstanding the potential for longer-term air quality and fire protection benefits, prescribed Notwithstanding the potential for longer-term air quality and fire protection benefits, prescribed
fires may have near-term implications for compliance with federal air quality standards. EPA’s fires may have near-term implications for compliance with federal air quality standards. EPA’s
exceptional events guidance describes conditions under which states and tribes can demonstrate exceptional events guidance describes conditions under which states and tribes can demonstrate
that air quality impacts from prescribed that air quality impacts from prescribed ~~fires57~~fires60 should be excluded from NAAQS compliance should be excluded from NAAQS compliance
determinations.determinations.5861 In particular, the guidance discusses how to demonstrate that a prescribed fire In particular, the guidance discusses how to demonstrate that a prescribed fire
“caused the event-related exceedance(s) or violation(s), was not reasonably controllable or “caused the event-related exceedance(s) or violation(s), was not reasonably controllable or
preventable, and is unlikely to recur at a particular location.”preventable, and is unlikely to recur at a particular location.”5962
As Congress deliberates on wildfire legislation, it may consider which monitoring strategies As Congress deliberates on wildfire legislation, it may consider which monitoring strategies
effectively inform smoke management and public health responses. Monitoring strategies may effectively inform smoke management and public health responses. Monitoring strategies may
include some combination of stationary monitors, mobile sensors, or models. Congress may also include some combination of stationary monitors, mobile sensors, or models. Congress may also
consider monitoring costs, which may vary by location, along with public health benefits. consider monitoring costs, which may vary by location, along with public health benefits.
In addition, Congress may continue to consider legislation related to prescribed fires. In the 116th In addition, Congress may continue to consider legislation related to prescribed fires. In the 116th
Congress, some Members introduced legislation to increase the frequency and scale of prescribed Congress, some Members introduced legislation to increase the frequency and scale of prescribed
~~burns as part of a broader strategy to mitigate future wildfire risk.60 Deliberations around such~~
~~proposals may consider the potential barriers to prescribed burns. Some have expressed concern~~
~~that resource limitations and, in some cases, regulatory requirements, may deter the use of~~
~~prescribed fires.61 Among other things, Congress may consider whether exceptional event~~
~~demonstrations—which are determined on a case-by-case basis and may be resource intensive—~~
~~balance air quality objectives with regulatory certainty and resource constraints.~~

54 55 AirNow, Fire and Smoke Map, https://fire.airnow.gov/. 56 2019 Wildfire Smoke Guide, p. 3. 57 Prescribed fuel and weather conditions may include fuel moisture content, relative humidity, and wind speed. For Prescribed fuel and weather conditions may include fuel moisture content, relative humidity, and wind speed. For
more information about prescribed burning and other measures to reduce fuel levels (e.g., dead wood) for fire more information about prescribed burning and other measures to reduce fuel levels (e.g., dead wood) for fire
protection, see CRS Report R40811, protection, see CRS Report R40811, Wildfire Fuels and Fuel Reduction, by Katie Hoover. , by Katie Hoover.
5558 Courtney A. Schultz, Sarah M. McCaffrey, and Heidi R. Huber-Stearns, “Policy Barriers and Opportunities for Courtney A. Schultz, Sarah M. McCaffrey, and Heidi R. Huber-Stearns, “Policy Barriers and Opportunities for
Prescribed Fire Application in the Western United States,” Prescribed Fire Application in the Western United States,” International Journal of Wildland Fire, vol. 28 (2019). , vol. 28 (2019).
5659 National Wildlife Coordinating Group, National Wildlife Coordinating Group, NWCG Smoke Management Guide for Prescribed Fire, PMS 420-3, , PMS 420-3,
November 2020, https://www.nwcg.gov/sites/default/files/publications/pms420-3.pdf. November 2020, https://www.nwcg.gov/sites/default/files/publications/pms420-3.pdf.
5760 For purposes of exceptional event demonstrations, EPA has defined For purposes of exceptional event demonstrations, EPA has defined prescribed fire as “any fire intentionally ignited as “any fire intentionally ignited
by management actions in accordance with applicable laws, policies, and regulations to meet specific land or resource by management actions in accordance with applicable laws, policies, and regulations to meet specific land or resource
management objectives” (40 C.F.R. §50.1). management objectives” (40 C.F.R. §50.1).
5861 EPA, “Exceptional Events Guidance: Prescribed Fire on Wildland that May Influence Ozone and Particulate Matter EPA, “Exceptional Events Guidance: Prescribed Fire on Wildland that May Influence Ozone and Particulate Matter
Concentrations,” August 19, 2019, https://www.epa.gov/air-quality-analysis/exceptional-events-guidance-prescribed-Concentrations,” August 19, 2019, https://www.epa.gov/air-quality-analysis/exceptional-events-guidance-prescribed-
fire-wildland-may-influence-ozone-and. Hereinafter, “2019 Exceptional Events Guidance.” fire-wildland-may-influence-ozone-and. Hereinafter, “2019 Exceptional Events Guidance.”
5962 2019 Exceptional Events Guidance. See also EPA, “EPA Releases Additional Resource on Prescribed Fires to 2019 Exceptional Events Guidance. See also EPA, “EPA Releases Additional Resource on Prescribed Fires to
Support Air Agencies,” press release, August 14, 2019, https://www.epa.gov/newsreleases/epa-releases-additional-Support Air Agencies,” press release, August 14, 2019, https://www.epa.gov/newsreleases/epa-releases-additional-
resource-prescribed-fires-support-air-agencies. resource-prescribed-fires-support-air-agencies.
~~60 S. 4626, National Prescribed Fire Act of 2020. Examples of proposed legislation related to prescribed fires from the~~
~~115th Congress include H.R. 7042, H.R. 4208, S. 1991, and S. 2068.~~
~~61 Courtney A. Schultz, Sarah M. McCaffrey, and Heidi R. Huber-Stearns, “Policy Barriers and Opportunities for~~
~~Prescribed Fire Application in the Western United States,” International Journal of Wildland Fire, vol. 28 (2019).~~
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11

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Congressional Research Service 11 Clean Air Act Issues in the 117th Congress burns as part of a broader strategy to mitigate future wildfire risk.63 Deliberations around such proposals may consider the potential barriers to prescribed burns. Some have expressed concern that resource limitations and, in some cases, regulatory requirements, may deter the use of prescribed fires.64 Among other things, Congress may consider whether exceptional event demonstrations—which are determined on a case-by-case basis and may be resource intensive—balance air quality objectives with regulatory certainty and resource constraints. For more information about air quality requirements related to wildfires, see CRS Insight For more information about air quality requirements related to wildfires, see CRS Insight
IN11528, IN11528, Wildfire Smoke: Air Quality Concerns and Management, by Kate C. Shouse. , by Kate C. Shouse.
Review of Air Toxics Standards
The CAA directs EPA to promulgate emission standards for sources of the 187 hazardous air The CAA directs EPA to promulgate emission standards for sources of the 187 hazardous air
pollutants (HAPs), informally referred to as “air toxics,” that are listed in Section 112(b).pollutants (HAPs), informally referred to as “air toxics,” that are listed in Section 112(b).6265 In In
general, these standards, known as National Emission Standards for Hazardous Air Pollutants general, these standards, known as National Emission Standards for Hazardous Air Pollutants
(NESHAPs), require major (NESHAPs), require major ~~sources63~~sources66 to meet numeric emission limits that have been achieved in to meet numeric emission limits that have been achieved in
practice by the best-performing similar sources. These standards are generally referred to as practice by the best-performing similar sources. These standards are generally referred to as
Maximum Achievable Control Technology (MACT) standards. The CAA also requires EPA to Maximum Achievable Control Technology (MACT) standards. The CAA also requires EPA to
conduct certain reviews of the MACT standards.conduct certain reviews of the MACT standards.6467
The remainder of this section highlights some of the air toxics issues that may garner interest in The remainder of this section highlights some of the air toxics issues that may garner interest in
the 117th Congress. the 117th Congress.
Mercury from Power Plants: EPA’s Consideration of Co-Benefits
In 2020, EPA promulgated the latest in a series of rulemakings on mercury from power plants In 2020, EPA promulgated the latest in a series of rulemakings on mercury from power plants
based on its review of the benefits and costs of reducing mercury and other HAPs from coal- and based on its review of the benefits and costs of reducing mercury and other HAPs from coal- and
oil-fired power plants. As explained below, the 2020 rulemaking revealed a change in EPA’s oil-fired power plants. As explained below, the 2020 rulemaking revealed a change in EPA’s
interpretation of a statutory provision—Section 112(n)(1)—that was expected to set a precedent interpretation of a statutory provision—Section 112(n)(1)—that was expected to set a precedent
for EPA’s consideration of benefits under other CAA authorities. It remains uncertain whether the for EPA’s consideration of benefits under other CAA authorities. It remains uncertain whether the
Biden Administration will retain that interpretation. Congress may conduct oversight and consider Biden Administration will retain that interpretation. Congress may conduct oversight and consider
how the agency factors benefits and costs into regulatory decisions. how the agency factors benefits and costs into regulatory decisions.
EPA concluded in 2020 that limits on HAPs from coal- and oil-fired power plants are not EPA concluded in 2020 that limits on HAPs from coal- and oil-fired power plants are not
“appropriate and necessary” (A&N) under CAA Section 112(n)(1).“appropriate and necessary” (A&N) under CAA Section 112(n)(1).6568 The 2020 A&N rule The 2020 A&N rule
reversed prior A&N determinations that led to the 2000 listing of coal- and oil-fired power plants reversed prior A&N determinations that led to the 2000 listing of coal- and oil-fired power plants
~~as a major source of HAPs and the 2012 Mercury and Air Toxics Standards (MATS) limiting~~
~~those HAPs. EPA’s accompanying analysis, published in 2011, projected annual benefits between~~
~~$37 billion and $90 billion in 2016. Nearly all of the monetized benefits were from the rule’s~~
~~particulate matter co-benefits. EPA monetized one of the expected mercury impacts—intelligence~~
~~quotient loss to children exposed to mercury from recreationally caught freshwater fish—but~~
~~could not monetize other mercury impacts. Such nonmonetized impacts may include other~~
~~neurologic effects (e.g., memory and behavior), cardiovascular effects, and effects on wildlife.~~
~~Factors that precluded comprehensively monetizing mercury and other HAP benefits from the~~
~~MATS rule included gaps in toxicological data, uncertainties in estimating human effects based~~

62 63 S. 4625, National Prescribed Fire Act of 2020. Examples of proposed legislation related to prescribed fires from the 115th Congress include H.R. 7042, H.R. 4208, S. 1991, and S. 2068. 64 Courtney A. Schultz, Sarah M. McCaffrey, and Heidi R. Huber-Stearns, “Policy Barriers and Opportunities for Prescribed Fire Application in the Western United States,” International Journal of Wildland Fire, vol. 28 (2019). 65 42 U.S.C. §7412. The 1990 CAA amendments specified 189 pollutants, but P.L. 102-187, enacted on December 4, 42 U.S.C. §7412. The 1990 CAA amendments specified 189 pollutants, but P.L. 102-187, enacted on December 4,
1991, deleted hydrogen sulfide from the list of toxic pollutants, leaving only 188. On December 19, 2005, EPA 1991, deleted hydrogen sulfide from the list of toxic pollutants, leaving only 188. On December 19, 2005, EPA
removed methyl ethyl ketone (MEK) from the list of toxic air pollutants. The total number of listed air toxics is now removed methyl ethyl ketone (MEK) from the list of toxic air pollutants. The total number of listed air toxics is now
187. 187.
6366 CAA §112(a) defines a CAA §112(a) defines a major source as “any stationary source or group of stationary sources located within a as “any stationary source or group of stationary sources located within a
contiguous area and under common control that emits or has the potential to emit considering controls, in the aggregate, contiguous area and under common control that emits or has the potential to emit considering controls, in the aggregate,
10 tons per year or more of any hazardous air pollutant or 25 tons per year or more of any combination of hazardous air 10 tons per year or more of any hazardous air pollutant or 25 tons per year or more of any combination of hazardous air
pollutants” 42 U.S.C. §7412(a)(1). pollutants” 42 U.S.C. §7412(a)(1).
6467 CAA §112(f)(2), codified at 42 U.S.C. §7412(f)(2). CAA §112(f)(2), codified at 42 U.S.C. §7412(f)(2).
6568 EPA, “National Emission Standards for Hazardous Air Pollutants: Coal- and Oil-Fired Electric Utility Steam EPA, “National Emission Standards for Hazardous Air Pollutants: Coal- and Oil-Fired Electric Utility Steam
Generating Units—Reconsideration of Supplemental Finding and Residual Risk and Technology Review,” 85Generating Units—Reconsideration of Supplemental Finding and Residual Risk and Technology Review,” 85 Federal
Register 31286, May 22, 2020. 31286, May 22, 2020.
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as a major source of HAPs and the 2012 Mercury and Air Toxics Standards (MATS) limiting those HAPs. EPA’s accompanying analysis, published in 2011, projected annual benefits between $37 billion and $90 billion in 2016. Nearly all of the monetized benefits were from the rule’s particulate matter co-benefits. EPA monetized one of the expected mercury impacts—intelligence quotient loss to children exposed to mercury from recreationally caught freshwater fish—but could not monetize other mercury impacts. Such nonmonetized impacts may include other neurologic effects (e.g., memory and behavior), cardiovascular effects, and effects on wildlife. Factors that precluded comprehensively monetizing mercury and other HAP benefits from the MATS rule included gaps in toxicological data, uncertainties in estimating human effects based on animal experiments, and insufficient economic research to translate the health and on animal experiments, and insufficient economic research to translate the health and
environmental effects to dollar value terms. environmental effects to dollar value terms.
EPA stated that the 2020 A&N rule corrects errors in the agency’s consideration of benefits in a EPA stated that the 2020 A&N rule corrects errors in the agency’s consideration of benefits in a
prior A&N finding. In its determination for the 2020 A&N rule, EPA excluded from consideration prior A&N finding. In its determination for the 2020 A&N rule, EPA excluded from consideration
any co-benefits to human health from reductions in pollutants any co-benefits to human health from reductions in pollutants not targeted by MATS. While EPA targeted by MATS. While EPA
acknowledged that estimation of all benefits and costs, including ancillary impacts, is consistent acknowledged that estimation of all benefits and costs, including ancillary impacts, is consistent
with federal guidance, the agency concluded that it had erred when it gave equal consideration to with federal guidance, the agency concluded that it had erred when it gave equal consideration to
benefits (HAP reductions) and co-benefits (non-HAP reductions) when making its prior A&N benefits (HAP reductions) and co-benefits (non-HAP reductions) when making its prior A&N
finding under Section 112(n).finding under Section 112(n).6669 The 2020 A&N rule concluded that an A&N finding under The 2020 A&N rule concluded that an A&N finding under
Section 112(n)(1) must instead be justified “overwhelmingly” by HAP reduction benefits. Section 112(n)(1) must instead be justified “overwhelmingly” by HAP reduction benefits.
Notwithstanding the 2020 A&N rule, the 2012 MATS limits remain in effect for power plants Notwithstanding the 2020 A&N rule, the 2012 MATS limits remain in effect for power plants
because EPA determined that it could not meet the criteria under CAA Section 112(c)(9) to delist because EPA determined that it could not meet the criteria under CAA Section 112(c)(9) to delist
them. Furthermore, the A&N finding does not change the regulatory status of other pollution them. Furthermore, the A&N finding does not change the regulatory status of other pollution
sources because CAA Section 112(n)(1) applies only to power plants. sources because CAA Section 112(n)(1) applies only to power plants.
Some have raised questions about why EPA reversed the A&N finding and how it might affect Some have raised questions about why EPA reversed the A&N finding and how it might affect
regulated entities. For example, some power plant owners are concerned the A&N reversal may regulated entities. For example, some power plant owners are concerned the A&N reversal may
compromise their ability to recover from ratepayers the costs of installing MATS pollution compromise their ability to recover from ratepayers the costs of installing MATS pollution
controls. Others find this unlikely, but legal challenges to the 2020 A&N rule are under way. For controls. Others find this unlikely, but legal challenges to the 2020 A&N rule are under way. For
more information about the legal issues, see CRS In Focus IF11622, more information about the legal issues, see CRS In Focus IF11622, Judicial Review of Mercury
and Air Toxics Regulations, by Kate R. Bowers and Linda Tsang. , by Kate R. Bowers and Linda Tsang.
The May 2020 A&N rule was a final action. The Biden Administration has the option to modify The May 2020 A&N rule was a final action. The Biden Administration has the option to modify
or repeal the 2020 A&N rule, but it would need to follow the same process used to promulgate or repeal the 2020 A&N rule, but it would need to follow the same process used to promulgate
new rules. The Biden Administration has directed the EPA Administrator to review the 2020 A&N new rules. The Biden Administration has directed the EPA Administrator to review the 2020 A&N
rule in accordance with E.O. 13990.rule in accordance with E.O. 13990.6770 Specifically, EPA is to consider taking action—suspending, Specifically, EPA is to consider taking action—suspending,
revising, or rescinding—on the 2020 A&N rule through a notice-and-comment proposed revising, or rescinding—on the 2020 A&N rule through a notice-and-comment proposed
~~rulemaking by August 2021.68~~
~~Congress may consider development of legislation that addresses how EPA and other federal~~
~~agencies factor benefits and costs into rulemaking decisions. For example, Congress may explore~~
~~opportunities to clarify how much weight an agency gives to benefits and ancillary impacts. Such~~
~~legislation may involve consideration of the tension between providing more specific direction to~~
~~the agencies and allowing an agency sufficient discretion to tailor its approach as warranted.~~
~~While legislative direction may provide greater consistency across Administrations, it may also~~
~~limit an agency’s discretion to consider case-specific factors and apply its evolving understanding~~
~~of the science and economics.~~

66 69 In 2012, EPA reaffirmed the 2000 A&N finding and promulgated the Mercury and Air Toxics Standards In 2012, EPA reaffirmed the 2000 A&N finding and promulgated the Mercury and Air Toxics Standards
Rule. Numerous parties petitioned the courts to review MATS. Among other things, some petitioners disagreed with Rule. Numerous parties petitioned the courts to review MATS. Among other things, some petitioners disagreed with
EPA’s conclusion that it was not appropriate to consider costs when making an A&N finding under CAA §112. In EPA’s conclusion that it was not appropriate to consider costs when making an A&N finding under CAA §112. In
2015, the Supreme Court agreed with the petitioners and remanded the rule for further consideration, but it did not 2015, the Supreme Court agreed with the petitioners and remanded the rule for further consideration, but it did not
address whether EPA has authority to consider monetized co-benefits in evaluating the cost of MATS (address whether EPA has authority to consider monetized co-benefits in evaluating the cost of MATS (Michigan v.
EPA, 135 S. Ct. 2699 (2015)). In 2016, EPA finalized a supplemental A&N finding based on its review of the 2012 , 135 S. Ct. 2699 (2015)). In 2016, EPA finalized a supplemental A&N finding based on its review of the 2012
rule’s estimated costs. EPA concluded that it was appropriate and necessary to regulate mercury and other HAPs from rule’s estimated costs. EPA concluded that it was appropriate and necessary to regulate mercury and other HAPs from
power plants after considering regulatory costs. power plants after considering regulatory costs.
6770 E.O. 13990 requires federal agencies to review “all existing regulations, orders, guidance documents, policies, and E.O. 13990 requires federal agencies to review “all existing regulations, orders, guidance documents, policies, and
any other similar agency actions” taken during the Trump Administration and to consider “suspending, revising, or any other similar agency actions” taken during the Trump Administration and to consider “suspending, revising, or
rescinding” agency actions that are deemed inconsistent with the order’s stated policy concerning protection of public rescinding” agency actions that are deemed inconsistent with the order’s stated policy concerning protection of public
health and the environment and addressing climate change. health and the environment and addressing climate change.
~~68 E.O. 13990, §2(iv).~~
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rulemaking by August 2021.71 As of this report’s publication date, EPA has not issued rulemaking actions related to the 2020 A&N rule. Congress may consider development of legislation that addresses how EPA and other federal agencies factor benefits and costs into rulemaking decisions. For example, Congress may explore opportunities to clarify how much weight an agency gives to benefits and ancillary impacts. Such legislation may involve consideration of the tension between providing more specific direction to the agencies and allowing an agency sufficient discretion to tailor its approach as warranted. While legislative direction may provide greater consistency across Administrations, it may also limit an agency’s discretion to consider case-specific factors and apply its evolving understanding of the science and economics. Ethylene Oxide: EPA’s Review of Emission Standards
Ethylene oxide is a flammable, colorless gas used to sterilize medical equipment, fumigate spices, Ethylene oxide is a flammable, colorless gas used to sterilize medical equipment, fumigate spices,
and make products such as antifreeze, textiles, and plastics. It has also long been considered and make products such as antifreeze, textiles, and plastics. It has also long been considered
~~mutagenic69~~mutagenic72 and has been associated with certain risks to human health. and has been associated with certain risks to human health.7073 Congress listed Congress listed
ethylene oxide as a hazardous air pollutant under the 1990 CAA amendments.ethylene oxide as a hazardous air pollutant under the 1990 CAA amendments.7174 EPA has EPA has
promulgated various regulations under CAA Section 112 to limit ethylene oxide emissions from promulgated various regulations under CAA Section 112 to limit ethylene oxide emissions from
the following sources: chemical manufacturers (synthetic organic chemical manufacturing, the following sources: chemical manufacturers (synthetic organic chemical manufacturing,
miscellaneous organic chemical manufacturers, polyether polyols production) and sterilizers miscellaneous organic chemical manufacturers, polyether polyols production) and sterilizers
(commercial sterilizers and hospital ethylene oxide sterilizers).(commercial sterilizers and hospital ethylene oxide sterilizers).7275
2018 National Air Toxics Assessment
EPA’s 2018 National Air Toxics Assessment (NATA) estimated that ethylene oxide significantly EPA’s 2018 National Air Toxics Assessment (NATA) estimated that ethylene oxide significantly
contributes to potential elevated cancer risks in some areas.contributes to potential elevated cancer risks in some areas.7376 The 2018 NATA was based on The 2018 NATA was based on
emissions data from 2014 and computer modeling as well as information about health effects, emissions data from 2014 and computer modeling as well as information about health effects,
including the ethylene oxide carcinogenicity assessment that EPA had updated in 2016.including the ethylene oxide carcinogenicity assessment that EPA had updated in 2016.7477 EPA’s EPA’s
2016 carcinogenicity assessment for ethylene oxide concluded that it is carcinogenic to humans.2016 carcinogenicity assessment for ethylene oxide concluded that it is carcinogenic to humans.7578
As noted by EPA, NATA is intended as a screening tool designed to help identify which As noted by EPA, NATA is intended as a screening tool designed to help identify which
~~pollutants, emission sources, and geographic areas to focus further evaluation of risks and~~
~~determine whether additional regulatory action may be warranted.~~
~~Stakeholders have expressed varying concerns. Some, such as the American Chemistry Council~~
~~and the Texas Commission on Environmental Quality, disagree with the NATA findings for~~
~~ethylene oxide, and recommend that EPA withdraw the ethylene oxide risk estimates.76 Others,~~
~~including environmental groups and some states and local communities, have expressed concerns~~
~~about exposure to ethylene oxide emissions based on NATA findings and other relevant~~

69 71 E.O. 13990, §2(iv). 72 A mutagen can change the genetic code in a cell. Chronic exposure to elevated levels of ethylene oxide has been A mutagen can change the genetic code in a cell. Chronic exposure to elevated levels of ethylene oxide has been
associated with the development of certain cancers based on animal studies. EPA, associated with the development of certain cancers based on animal studies. EPA, Evaluation of the Inhalation
Carcinogenicity of Ethylene Oxide (CASRN 75-21-8) in Support of Summary Information on the Integrated Risk
Information System (IRIS), EPA/635/R-16/350Fa, December 2016, https://cfpub.epa.gov/ncea/iris/iris_documents/, EPA/635/R-16/350Fa, December 2016, https://cfpub.epa.gov/ncea/iris/iris_documents/
documents/toxreviews/1025tr.pdf. Hereinafter, “2016 IRIS EtO”. documents/toxreviews/1025tr.pdf. Hereinafter, “2016 IRIS EtO”.
7073 For example, acute exposures to ethylene oxide are associated with respiratory irritation and effects to the nervous For example, acute exposures to ethylene oxide are associated with respiratory irritation and effects to the nervous
system. system.
7174 Additional statutes apply to various uses of ethylene oxide. For example, the distribution, sale, and use of ethylene Additional statutes apply to various uses of ethylene oxide. For example, the distribution, sale, and use of ethylene
oxide as a sterilant is regulated by EPA under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA); see 7 oxide as a sterilant is regulated by EPA under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA); see 7
U.S.C. §136 et seq. This report focuses on CAA requirements. U.S.C. §136 et seq. This report focuses on CAA requirements.
7275 For more information about the source categories, see EPA, For more information about the source categories, see EPA, Strategy for Reviewing Ethylene Oxide Emissions, ,
https://www.epa.gov/hazardous-air-pollutants-ethylene-oxide/agency-actions-ethylene-oxide#regulations. https://www.epa.gov/hazardous-air-pollutants-ethylene-oxide/agency-actions-ethylene-oxide#regulations.
7376 EPA, “2014 National Air Toxics Assessment,” https://www.epa.gov/national-air-toxics-assessment/2014-national- EPA, “2014 National Air Toxics Assessment,” https://www.epa.gov/national-air-toxics-assessment/2014-national-
air-toxics-assessment. air-toxics-assessment.
7477 EPA, “NATA Frequent Questions,” https://www.epa.gov/national-air-toxics-assessment/nata-frequent-questions. EPA, “NATA Frequent Questions,” https://www.epa.gov/national-air-toxics-assessment/nata-frequent-questions.
7578 EPA’s prior assessment, completed in 1985, concluded that ethylene oxide is “probably carcinogenic to humans”; see EPA’s prior assessment, completed in 1985, concluded that ethylene oxide is “probably carcinogenic to humans”; see
EPA, “Ethylene Oxide Emissions Standards for Sterilization Facilities,” 67 EPA, “Ethylene Oxide Emissions Standards for Sterilization Facilities,” 67 Federal Register 17715, April 7, 2006. In 17715, April 7, 2006. In
2016, EPA changed the classification to “carcinogenic to humans” based on occupational epidemiological studies; see 2016, EPA changed the classification to “carcinogenic to humans” based on occupational epidemiological studies; see
2016 IRIS EtO. 2016 IRIS EtO.
~~76 The American Chemistry Council, which represents producers and consumers of ethylene oxide, submitted a Request~~
~~for Correction under the Information Quality Act asking that the “NATA risk estimates for [ethylene oxide] be~~
~~withdrawn and corrected to reflect scientifically supportable risk values.” See EPA, “National Emission Standards for~~
~~Hazardous Air Pollutants: Miscellaneous Organic Chemical Manufacturing Residual Risk and Technology Review,”~~
~~proposed rule, 84 Federal Register 69218, December 17, 2019.~~
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~~Clean Air Act Issues in the 117th Congress~~

Congressional Research Service 14 Clean Air Act Issues in the 117th Congress pollutants, emission sources, and geographic areas to focus further evaluation of risks and determine whether additional regulatory action may be warranted. Stakeholders have expressed varying concerns. Some, such as the American Chemistry Council and the Texas Commission on Environmental Quality, disagree with the NATA findings for ethylene oxide, and recommend that EPA withdraw the ethylene oxide risk estimates.79 Others, including environmental groups and some states and local communities, have expressed concerns about exposure to ethylene oxide emissions based on NATA findings and other relevant information, and have urged EPA to strengthen the emission standards. Some Members of information, and have urged EPA to strengthen the emission standards. Some Members of
Congress have questioned whether the current standards for sources of ethylene oxide afford Congress have questioned whether the current standards for sources of ethylene oxide afford
adequate protection of human health and have introduced legislation in prior sessions of adequate protection of human health and have introduced legislation in prior sessions of
Congress.Congress.7780
Residual Risk and Technology Review
The CAA requires EPA to conduct two kinds of reviews of the MACT standards—the residual The CAA requires EPA to conduct two kinds of reviews of the MACT standards—the residual
risk review and the technology review. For the residual risk review, the CAA requires EPA to risk review and the technology review. For the residual risk review, the CAA requires EPA to
evaluate MACT standards within eight years of promulgation to determine whether revisions are evaluate MACT standards within eight years of promulgation to determine whether revisions are
needed to address any remaining risk associated with HAP emissions from the source category.needed to address any remaining risk associated with HAP emissions from the source category.7881
EPA’s residual risk review considers whether revisions to the MACT standards are required to EPA’s residual risk review considers whether revisions to the MACT standards are required to
provide an ample margin of safety to protect public health or to prevent an adverse environmental provide an ample margin of safety to protect public health or to prevent an adverse environmental
effect, taking into consideration factors such as costs.effect, taking into consideration factors such as costs.7982 For the technology review, the CAA For the technology review, the CAA
requires EPA to review the MACT standards and revise as needed, after considering requires EPA to review the MACT standards and revise as needed, after considering
“developments in practices, processes, and control technologies” every eight years.“developments in practices, processes, and control technologies” every eight years.8083 EPA often EPA often
combines the two reviews into one, known as the combines the two reviews into one, known as the residual risk and technology review. .
In 2020, EPA completed the statutorily required residual risk and technology review of the In 2020, EPA completed the statutorily required residual risk and technology review of the
miscellaneous organic chemical manufacturing (MON) NESHAP, which includes limits on miscellaneous organic chemical manufacturing (MON) NESHAP, which includes limits on
ethylene oxide and other HAPs.ethylene oxide and other HAPs.8184 EPA revised the MON NESHAP based on this review and EPA revised the MON NESHAP based on this review and
published the final rule on August 12, 2020.published the final rule on August 12, 2020.8285 Among other things, EPA promulgated additional Among other things, EPA promulgated additional
requirements to limit ethylene oxide from process vents, storage tanks, and equipment leaks at requirements to limit ethylene oxide from process vents, storage tanks, and equipment leaks at
major sources. The revised requirements to limit ethylene oxide were based on the residual risk major sources. The revised requirements to limit ethylene oxide were based on the residual risk
review. EPA used the updated risk values for ethylene oxide in its residual risk review and review. EPA used the updated risk values for ethylene oxide in its residual risk review and
concluded that, absent revisions to the MON standards, the “risks are unacceptable.”concluded that, absent revisions to the MON standards, the “risks are unacceptable.”83
~~EPA’s review of the standards limiting ethylene oxide from commercial sterilizers is under way.~~
~~This source category includes medical equipment suppliers, pharmaceutical suppliers, other~~
~~health-related industries, spice manufacturers, and contract sterilizers.84 Some Members of~~
~~Congress have urged EPA to “exercise its full authority to regulate” ethylene oxide under the~~
~~CAA and to conduct a residual risk review along with the statutorily mandated technology review~~
~~for the source category.85 EPA published an advanced notice of proposed rulemaking (ANPR) in~~
~~late 2019 that requested information “on potential control measures for reducing ethylene oxide~~
~~emissions from commercial sterilization and fumigation operations.”86 The ANPR also discussed~~

7786 79 The American Chemistry Council, which represents producers and consumers of ethylene oxide, submitted a Request for Correction under the Information Quality Act asking that the “NATA risk estimates for [ethylene oxide] be withdrawn and corrected to reflect scientifically supportable risk values.” See EPA, “National Emission Standards for Hazardous Air Pollutants: Miscellaneous Organic Chemical Manufacturing Residual Risk and Technology Review,” proposed rule, 84 Federal Register 69218, December 17, 2019. 80 Examples of legislative proposals from the 116th Congress include H.R. 1152/S. 458 and H.R. 7822/S. 4369. Examples of legislative proposals from the 116th Congress include H.R. 1152/S. 458 and H.R. 7822/S. 4369.
7881 CAA §112(f)(2), codified at 42 U.S.C. §7412(f)(2). CAA §112(f)(2), codified at 42 U.S.C. §7412(f)(2).
7982 42 U.S.C. §7412(f)(2). 42 U.S.C. §7412(f)(2).
8083 CAA §112(d)(6), codified at 42 U.S.C. §7412(d)(6). CAA §112(d)(6), codified at 42 U.S.C. §7412(d)(6).
8184 EPA was under court order to complete the CAA §112 risk and technology review of the MON NESHAP and 32 EPA was under court order to complete the CAA §112 risk and technology review of the MON NESHAP and 32
other NESHAPs. Order, Cal. Communities Against Toxics, et al. v. Pruitt, No. 1:15-cv-00512-TSC, Doc. No. 49 other NESHAPs. Order, Cal. Communities Against Toxics, et al. v. Pruitt, No. 1:15-cv-00512-TSC, Doc. No. 49
(D.D.C. Mar. 13, 2017). (D.D.C. Mar. 13, 2017).
8285 EPA, “National Emission Standards for Hazardous Air Pollutants: Miscellaneous Organic Chemical Manufacturing EPA, “National Emission Standards for Hazardous Air Pollutants: Miscellaneous Organic Chemical Manufacturing
Residual Risk and Technology Review,” final rule, 85Residual Risk and Technology Review,” final rule, 85 Federal Register 49084, August 12, 2020. Hereinafter, “MON 49084, August 12, 2020. Hereinafter, “MON
Final Rule.” Final Rule.”
8386 MON Final Rule, p. 49097. Congressional Research Service 15 Clean Air Act Issues in the 117th Congress EPA’s review of the standards limiting ethylene oxide from commercial sterilizers is under way. This source category includes medical equipment suppliers, pharmaceutical suppliers, other health-related industries, spice manufacturers, and contract sterilizers.87 Some Members of Congress have urged EPA to “exercise its full authority to regulate” ethylene oxide under the CAA and to conduct a residual risk review along with the statutorily mandated technology review for the source category.88 EPA published an advanced notice of proposed rulemaking (ANPR) in late 2019 that requested information “on potential control measures for reducing ethylene oxide emissions from commercial sterilization and fumigation operations.”89 The ANPR also discussed ~~MON Final Rule, p. 49097.~~
~~84 EPA, Strategy for Reviewing Ethylene Oxide Emissions, https://www.epa.gov/hazardous-air-pollutants-ethylene-~~
~~oxide/agency-actions-ethylene-oxide#regulations.~~
~~85 Letter from Senator Tammy Duckworth et al. to Honorable Andrew Wheeler, EPA Administrator, July 8, 2020.~~
~~86 EPA, “National Emission Standards for Hazardous Air Pollutants: Ethylene Oxide Commercial Sterilization and~~
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~~Clean Air Act Issues in the 117th Congress~~

small business considerations, noting that EPA has identified about 35 facilities owned by small small business considerations, noting that EPA has identified about 35 facilities owned by small
businesses within the commercial sterilizer source category.businesses within the commercial sterilizer source category.8790 According to the ANPR, EPA According to the ANPR, EPA
intends to convene a Small Business Advocacy Review Panel before it takes “any significant intends to convene a Small Business Advocacy Review Panel before it takes “any significant
regulatory action.”regulatory action.”8891 The The ~~Trump~~Biden Administration Administration ~~published a regulatory agenda in fall 2020, which~~
~~estimated that EPA will propose a decision about whether and how to revise the commercial~~
~~sterilizer NESHAP in March 2021.89~~
stated that EPA expects to issue a proposal for commercial sterilizers in 2021 and that the agency is beginning to review regulations for other facilities that emit ethylene oxide.92 As of this report’s publication date, EPA has not proposed this rule for commercial sterilizers. Congress may conduct oversight as EPA reviews the commercial sterilizer standards and seek Congress may conduct oversight as EPA reviews the commercial sterilizer standards and seek
clarity from EPA on its plans for the remaining industrial categories that emit ethylene oxide.clarity from EPA on its plans for the remaining industrial categories that emit ethylene oxide.9093
Beyond oversight, Congress may consider whether the CAA provides adequate authority for EPA Beyond oversight, Congress may consider whether the CAA provides adequate authority for EPA
to evaluate or revise NESHAPs based on updated risk information. The U.S. District Court for the to evaluate or revise NESHAPs based on updated risk information. The U.S. District Court for the
Northern District of California recently ruled on the required frequency of residual risk review, Northern District of California recently ruled on the required frequency of residual risk review,
and specifically on whether the CAA requires EPA to conduct the residual risk review each time it and specifically on whether the CAA requires EPA to conduct the residual risk review each time it
revises the MACT standards for a source, or only after the initial promulgation of MACT revises the MACT standards for a source, or only after the initial promulgation of MACT
standards. The court concluded that the CAA does not impose “a mandatory duty on EPA to standards. The court concluded that the CAA does not impose “a mandatory duty on EPA to
revisit its risk-based standards for hazardous pollution sources whenever the agency revises” the revisit its risk-based standards for hazardous pollution sources whenever the agency revises” the
MACT standards.MACT standards.9194
Congress may consider the implications of the court’s finding, in particular when updated risk Congress may consider the implications of the court’s finding, in particular when updated risk
information would alter the conclusions of EPA’s residual risk reviews. EPA completed a residual information would alter the conclusions of EPA’s residual risk reviews. EPA completed a residual
~~risk review for commercial sterilizers in 2006—a decade before EPA revised the risk value for~~
~~ethylene oxide.92 It is unknown whether the updated risk value for ethylene oxide would lead EPA~~
~~to a different decision about the stringency of the standard. While CAA Section 112(f)(2)~~
~~identifies factors to inform EPA’s consideration of whether revisions are required, the act does~~
~~not specify the stringency of the standards that EPA must set. CAA Section 112(f)(2) allows EPA~~
~~to base revisions on both health-based and non-health-based factors.93~~

87 EPA, Strategy for Reviewing Ethylene Oxide Emissions, https://www.epa.gov/hazardous-air-pollutants-ethylene-oxide/agency-actions-ethylene-oxide#regulations. 88 Letter from Senator Tammy Duckworth et al. to Honorable Andrew Wheeler, EPA Administrator, July 8, 2020. 89 EPA, “National Emission Standards for Hazardous Air Pollutants: Ethylene Oxide Commercial Sterilization and Fumigation Operations,” advance notice of proposed rulemaking, 84Fumigation Operations,” advance notice of proposed rulemaking, 84 Federal Register 67889, December 12, 2019. 67889, December 12, 2019.
Hereinafter, “Sterilizer ANPR.” Hereinafter, “Sterilizer ANPR.”
8790 Sterilizer ANPR, p. 67893. EPA identified a total of 135 facilities in the commercial sterilizer source category. The Sterilizer ANPR, p. 67893. EPA identified a total of 135 facilities in the commercial sterilizer source category. The
Regulatory Flexibility Act (RFA) of 1980, 5. U.S.C. §§601-612, requires federal agencies to assess the impact of their Regulatory Flexibility Act (RFA) of 1980, 5. U.S.C. §§601-612, requires federal agencies to assess the impact of their
forthcoming regulations on small entities. The RFA also requires agencies to ensure that small entities have an forthcoming regulations on small entities. The RFA also requires agencies to ensure that small entities have an
opportunity to participate in the rulemaking process, and it has special requirements for proposed rules issued by EPA, opportunity to participate in the rulemaking process, and it has special requirements for proposed rules issued by EPA,
the Occupational Safety and Health Administration, and the Consumer Financial Protection Bureau. See CRS Report the Occupational Safety and Health Administration, and the Consumer Financial Protection Bureau. See CRS Report
RL32240, RL32240, The Federal Rulemaking Process: An Overview, coordinated by Maeve P. Carey. , coordinated by Maeve P. Carey.
8891 Sterilizer ANPR, p. 67894. Sterilizer ANPR, p. 67894.
~~89 Office of Management and Budget, “Fall 2020 Unified Agenda of Regulatory and Deregulatory Actions,”~~
~~EPA/OAR, RIN 2060-AU37, https://www.reginfo.gov/public/do/eAgendaViewRule?pubId=202010&RIN=2060-~~
~~AU37.~~
9092 EPA, Agency Actions on Ethylene Oxide, https://www.epa.gov/hazardous-air-pollutants-ethylene-oxide/agency-actions-ethylene-oxide#regulations. 93 EPA reported plans to “take a closer look at air toxics emissions standards for other industries that emit ethylene EPA reported plans to “take a closer look at air toxics emissions standards for other industries that emit ethylene
oxide to determine whether a review of those rules is needed. EPA will start this closer look with its air toxics oxide to determine whether a review of those rules is needed. EPA will start this closer look with its air toxics
emissions standards for commercial sterilizers.” See EPA, “Strategy for Reviewing Ethylene Oxide Emissions,” emissions standards for commercial sterilizers.” See EPA, “Strategy for Reviewing Ethylene Oxide Emissions,”
https://www.epa.gov/hazardous-air-pollutants-ethylene-oxide/agency-actions-ethylene-oxide#regulations, website last https://www.epa.gov/hazardous-air-pollutants-ethylene-oxide/agency-actions-ethylene-oxide#regulations, website last
updated on August 19, 2020. updated on August 19, 2020.
9194 Citizens for Pennsylvania’s Future v. Wheeler, 469 F. Supp. 3d 920, 922 (N.D. Cal. 2020). For more information, Citizens for Pennsylvania’s Future v. Wheeler, 469 F. Supp. 3d 920, 922 (N.D. Cal. 2020). For more information,
congressional clients may contact CRS Legislative Attorney Kate Bowers. congressional clients may contact CRS Legislative Attorney Kate Bowers.
~~92 In 2006, EPA determined no additional control requirements were warranted and therefore did not revise the ethylene~~
~~oxide sterilization NESHAP. EPA, “Ethylene Oxide Emissions Standards for Sterilization Facilities,” 71~~ ~~Federal~~
~~Register~~ ~~17712, April 7, 2006.~~
~~93 42 U.S.C. §7412(f)(2).~~
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Congressional Research Service 16 Clean Air Act Issues in the 117th Congress risk review for commercial sterilizers in 2006—a decade before EPA revised the risk value for ethylene oxide.95 It is unknown whether the updated risk value for ethylene oxide would lead EPA to a different decision about the stringency of the standard. While CAA Section 112(f)(2) identifies factors to inform EPA’s consideration of whether revisions are required, the act does not specify the stringency of the standards that EPA must set. CAA Section 112(f)(2) allows EPA to base revisions on both health-based and non-health-based factors.96 Source Classification: 2018 EPA Withdrawal of “Once In, Always In” Policy
Congress may conduct oversight related to a 2020 EPA rulemaking pertaining to the two kinds of Congress may conduct oversight related to a 2020 EPA rulemaking pertaining to the two kinds of
sources of HAPs defined in CAA Section 112(a)—major sources and area sources.sources of HAPs defined in CAA Section 112(a)—major sources and area sources. 97 Most recently, the Biden Administration determined it would review this 2020 rulemaking pursuant to E.O. 13990 and propose a rule by the end of 2021.98 The 2020 The 2020
rulemaking allows major sources of HAPs to reclassify as an area source after meeting conditions rulemaking allows major sources of HAPs to reclassify as an area source after meeting conditions
to limit emissions below major source thresholds.to limit emissions below major source thresholds.9499 Major source refers to refers to
any stationary source or group of stationary sources located within a contiguous area and any stationary source or group of stationary sources located within a contiguous area and
under common control that emits or has the potential to emit considering controls, in the under common control that emits or has the potential to emit considering controls, in the
aggregate, 10 tons per year or more of any hazardous air pollutant or 25 tons per year or aggregate, 10 tons per year or more of any hazardous air pollutant or 25 tons per year or
more of any combination of hazardous air pollutants.more of any combination of hazardous air pollutants.95100
Area source refers to “any stationary source of hazardous air pollutants that is not a major refers to “any stationary source of hazardous air pollutants that is not a major
source.”source.”96101 Classification as a major or area source has implications for which emission standards Classification as a major or area source has implications for which emission standards
apply to the source. Major sources are subject to the technology-based emission standards—apply to the source. Major sources are subject to the technology-based emission standards—
MACT standards—as well as monitoring, recordkeeping, and reporting requirements. Area MACT standards—as well as monitoring, recordkeeping, and reporting requirements. Area
sources are typically subject to lesser controls than major sources. Under the CAA, EPA may sources are typically subject to lesser controls than major sources. Under the CAA, EPA may
elect to establish more lenient standards for area sources, known as generally available control elect to establish more lenient standards for area sources, known as generally available control
technologies, or GACT.technologies, or GACT.97102 In some cases, EPA has promulgated requirements for major sources In some cases, EPA has promulgated requirements for major sources
but not for area sources in some source categories, which means that HAPs from some area but not for area sources in some source categories, which means that HAPs from some area
sources are not regulated under the NESHAPs.sources are not regulated under the NESHAPs.98103
An EPA 1995 guidance memorandum first explained when a major source of HAPs could be An EPA 1995 guidance memorandum first explained when a major source of HAPs could be
reclassified as an area source.reclassified as an area source.99104 At the time, EPA was implementing the 1990 CAA amendments 95 In 2006, EPA determined no additional control requirements were warranted and therefore did not revise the ethylene oxide sterilization NESHAP. EPA, “Ethylene Oxide Emissions Standards for Sterilization Facilities,” 71 Federal Register 17712, April 7, 2006. 96 42 U.S.C. §7412(f)(2). 97 ~~At the time, EPA was implementing the 1990 CAA amendments~~
~~and various MACT standards were going into effect. EPA’s 1995 memorandum stated that major~~
~~sources of HAPs could “switch to area source status at any time until the ‘first compliance date’~~
~~of the standard.”100 EPA also discussed its “Once In, Always In” (OIAI) interpretation of the~~
~~CAA.101 Specifically, EPA determined that facilities that are major sources for HAPs on the “first~~
~~compliance date” would be “required to comply permanently with the MACT standard,” even if~~
~~the facility subsequently reduced emissions below the major source threshold.102 The 1995~~
~~memorandum concluded that the OIAI policy would ensure that emissions reductions were~~
~~maintained over time.103~~
~~EPA’s OIAI interpretation remained in effect until 2018, though EPA had previously considered~~
~~proposals that would have modified OIAI.104 In 2018, EPA withdrew the 1995 memorandum—~~

94 EPA, “Reclassification of Major Sources as Area Sources Under Section 112 of the Clean Air Act,” final rule, 85 EPA, “Reclassification of Major Sources as Area Sources Under Section 112 of the Clean Air Act,” final rule, 85
Federal Register 73854, November 19, 2020. Hereinafter, “2020 Reclassification Rule.” 73854, November 19, 2020. Hereinafter, “2020 Reclassification Rule.”
~~95 42 U.S.C. §7412(a)(1).~~
~~96 42 U.S.C. §7412(a)(1).~~
97 98 Office of Management and Budget, “Spring 2021 Unified Agenda of Regulatory and Deregulatory Actions,” EPA/OAR, RIN 2060-AV20, https://www.reginfo.gov/public/do/eAgendaViewRule?pubId=202104&RIN=2060-AV20. 99 2020 Reclassification Rule. 100 42 U.S.C. §7412(a)(1). 101 42 U.S.C. §7412(a)(1). 102 42 U.S.C. §7412(d)(5). See also CRS Report R43699, 42 U.S.C. §7412(d)(5). See also CRS Report R43699, Key Historical Court Decisions Shaping EPA’s Program
Under the Clean Air Act, by Linda Tsang. , by Linda Tsang.
98103 2020 Reclassification Rule, p. 73859. 2020 Reclassification Rule, p. 73859.
99104 Memorandum from John S. Seitz, Director, Office of Air Quality Planning and Standards, to EPA Regional Memorandum from John S. Seitz, Director, Office of Air Quality Planning and Standards, to EPA Regional
Directors, May 16, 1995, https://www.epa.gov/stationary-sources-air-pollution/guidance-reclassification-major-Directors, May 16, 1995, https://www.epa.gov/stationary-sources-air-pollution/guidance-reclassification-major-
sources-area-sources-under-section. Hereinafter, “1995 Memorandum.” sources-area-sources-under-section. Hereinafter, “1995 Memorandum.”
~~100 1995 Memorandum.~~
~~101 1995 Memorandum.~~
~~102 1995 Memorandum.~~
~~103 1995 Memorandum.~~
~~104 See (1) EPA, “National Emission Standards for Hazardous Air Pollutants for Source Categories: General~~
~~Provisions,” proposed rule, 68 Federal Register 26249, May 15, 2003; and (2) EPA, “National Emission Standards for~~
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Congressional Research Service 17 Clean Air Act Issues in the 117th Congress and various MACT standards were going into effect. EPA’s 1995 memorandum stated that major sources of HAPs could “switch to area source status at any time until the ‘first compliance date’ of the standard.”105 EPA also discussed its “Once In, Always In” (OIAI) interpretation of the CAA.106 Specifically, EPA determined that facilities that are major sources for HAPs on the “first compliance date” would be “required to comply permanently with the MACT standard,” even if the facility subsequently reduced emissions below the major source threshold.107 The 1995 memorandum concluded that the OIAI policy would ensure that emissions reductions were maintained over time.108 EPA’s OIAI interpretation remained in effect until 2018, though EPA had previously considered proposals that would have modified OIAI.109 In 2018, EPA withdrew the 1995 memorandum—and the OIAI interpretation—and issued a different CAA interpretation in a new guidance and the OIAI interpretation—and issued a different CAA interpretation in a new guidance
memorandum. EPA’s 2018 memorandum concluded that “Congress placed no temporal memorandum. EPA’s 2018 memorandum concluded that “Congress placed no temporal
limitations on the determination of whether a source emits or has the [potential to emit] HAP in limitations on the determination of whether a source emits or has the [potential to emit] HAP in
sufficient quantity to qualify as a major source,” and described conditions under which major sufficient quantity to qualify as a major source,” and described conditions under which major
sources could be reclassified to area sources.sources could be reclassified to area sources.~~105~~110 The 2020 final rulemaking (2020 Reclassification The 2020 final rulemaking (2020 Reclassification
Rule) codified the agency’s withdrawal of its 1995 guidance on source classification under Rule) codified the agency’s withdrawal of its 1995 guidance on source classification under
Section 112. Under the 2020 Reclassification Rule, a major source can be reclassified to area Section 112. Under the 2020 Reclassification Rule, a major source can be reclassified to area
source status at any time upon reducing its potential to emit HAP to below the major source source status at any time upon reducing its potential to emit HAP to below the major source
thresholds—10 tons per year of any single HAP and 25 tons per year of any combination of HAP, thresholds—10 tons per year of any single HAP and 25 tons per year of any combination of HAP,
upon approval of the source’s request.upon approval of the source’s request.~~106~~111
Members of Congress have expressed varying opinions about the change, with some Members Members of Congress have expressed varying opinions about the change, with some Members
supporting the rescission of the OIAI supporting the rescission of the OIAI ~~policy107~~policy112 and others urging EPA to retain it. and others urging EPA to retain it.~~108~~113 Much of the Much of the
debate about the 2020 Reclassification Rule has centered on whether and how it will affect HAP debate about the 2020 Reclassification Rule has centered on whether and how it will affect HAP
emissions. Supporters of the 2020 Reclassification Rule expect it will incentivize sources to emissions. Supporters of the 2020 Reclassification Rule expect it will incentivize sources to
reduce emissions below major source thresholds.reduce emissions below major source thresholds.~~109~~114 For example, facilities may be more likely to For example, facilities may be more likely to
pursue pollution reduction opportunities in exchange for the reduced regulatory obligations pursue pollution reduction opportunities in exchange for the reduced regulatory obligations
associated with area sources. Others have raised concerns that it could nonetheless lead to an associated with area sources. Others have raised concerns that it could nonetheless lead to an
~~increase in emissions from sources that stop complying with MACT standards, even if those~~
~~sources remain below major source thresholds. For example, if a major source elects to reclassify~~
~~as an area source, it would switch to area source standards, which may allow the facility to use~~
~~less effective controls or use the pollution controls less often compared to the MACT standards.110~~
~~EPA Region 9 raised this concern in 2004, when the agency considered a different proposal to~~
~~allow reclassification. At the time, EPA Region 9 commented that in “many instances, the MACT~~
~~requirements could lead to greater reductions when compared to sources accepting” enforceable~~
~~limits of 24 tons per year for a combination of HAPs and 9 tons per year for a single HAP.111~~
~~More recently, EPA reviewed permits and other information for 69 sources that reclassified to~~
~~area sources under the 2018 memorandum. EPA found that emissions increased at 1 of the 69~~
~~sources, and that 68 of the 69 sources “achieved and maintain area source status by operating the~~

105 1995 Memorandum. 106 1995 Memorandum. 107 1995 Memorandum. 108 1995 Memorandum. 109 See (1) EPA, “National Emission Standards for Hazardous Air Pollutants for Source Categories: General Provisions,” proposed rule, 68 Federal Register 26249, May 15, 2003; and (2) EPA, “National Emission Standards for Hazardous Air Pollutants for Source Categories: General Provisions,” proposed rule, 72 Hazardous Air Pollutants for Source Categories: General Provisions,” proposed rule, 72 Federal Register 69, January 69, January
3, 2007. EPA did not finalize the OIAI-related provisions from either of these proposals. 3, 2007. EPA did not finalize the OIAI-related provisions from either of these proposals.
~~105~~110 Memorandum from William L. Wehrum, EPA Assistant Administrator, to Regional Air Division Directors, January Memorandum from William L. Wehrum, EPA Assistant Administrator, to Regional Air Division Directors, January
25, 2018, https://www.epa.gov/stationary-sources-air-pollution/guidance-reclassification-major-sources-area-sources-25, 2018, https://www.epa.gov/stationary-sources-air-pollution/guidance-reclassification-major-sources-area-sources-
under-section. under-section.
~~106~~111 2020 Reclassification Rule, p. 73865. 2020 Reclassification Rule, p. 73865.
~~107~~112 For example, see U.S. Senate Environment and Public Works Committee, “Senators Call on EPA to Remove For example, see U.S. Senate Environment and Public Works Committee, “Senators Call on EPA to Remove
Burdensome ‘Once-In-Always-In’ Policy,” press release, January 9, 2018, https://www.epw.senate.gov/public/Burdensome ‘Once-In-Always-In’ Policy,” press release, January 9, 2018, https://www.epw.senate.gov/public/
index.cfm/2018/1/senators-call-on-epa-to-remove-burdensome-once-in-always-in-policy. index.cfm/2018/1/senators-call-on-epa-to-remove-burdensome-once-in-always-in-policy.
~~108~~113 For example, see Letter from Senator Carper et al. to EPA Administrator Pruitt, March 14, 2018, For example, see Letter from Senator Carper et al. to EPA Administrator Pruitt, March 14, 2018,
https://www.epw.senate.gov/public/_cache/files/1/3/131714ba-f373-4b43-bfb8-a3820ac63a50/https://www.epw.senate.gov/public/_cache/files/1/3/131714ba-f373-4b43-bfb8-a3820ac63a50/
6DCFBCE44BF189136EE1F2CC17E66B54.carper-markey-lead-democrats-in-urging-pruitt-to-reinstate-strict-air-6DCFBCE44BF189136EE1F2CC17E66B54.carper-markey-lead-democrats-in-urging-pruitt-to-reinstate-strict-air-
toxics-standards-for-the-country-s-dirtiest-industrial-sources.pdf. toxics-standards-for-the-country-s-dirtiest-industrial-sources.pdf.
~~109~~114 For example, see Letter from API to the EPA Docket, September 24, 2019, Docket ID EPA-HQ-OAR-2019-0282- For example, see Letter from API to the EPA Docket, September 24, 2019, Docket ID EPA-HQ-OAR-2019-0282-
0298, https://www.regulations.gov/document?D=EPA-HQ-OAR-2019-0282-0298. 0298, https://www.regulations.gov/document?D=EPA-HQ-OAR-2019-0282-0298.
~~110 For example, see Harvard Environmental & Energy Law Program, “Once In Always In Guidance for Major Sources~~
~~Under the Clean Air Act,” https://eelp.law.harvard.edu/2018/02/once-in-always-in-guidance-for-major-sources-under-~~
~~the-clean-air-act/.~~
~~111 Letter from Michael S. Bandrowski, Air Toxics Chief, EPA Region IX, to David Cozzie, Group Leader, EPA Office~~
~~of Air Quality Planning and Standards, December 13, 2005, p. 3, see EPA Docket ID EPA-HQ-OAR-2004-0094-0151.~~
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Congressional Research Service 18 Clean Air Act Issues in the 117th Congress increase in emissions from sources that stop complying with MACT standards, even if those sources remain below major source thresholds. For example, if a major source elects to reclassify as an area source, it would switch to area source standards, which may allow the facility to use less effective controls or use the pollution controls less often compared to the MACT standards.115 EPA Region 9 raised this concern in 2004, when the agency considered a different proposal to allow reclassification. At the time, EPA Region 9 commented that in “many instances, the MACT requirements could lead to greater reductions when compared to sources accepting” enforceable limits of 24 tons per year for a combination of HAPs and 9 tons per year for a single HAP.116 More recently, EPA reviewed permits and other information for 69 sources that reclassified to area sources under the 2018 memorandum. EPA found that emissions increased at 1 of the 69 sources, and that 68 of the 69 sources “achieved and maintain area source status by operating the emission controls or continuing to implement the practices they used to comply with the major emission controls or continuing to implement the practices they used to comply with the major
source NESHAP requirements.”source NESHAP requirements.”~~112~~117
EPA also identified source categories likely to be affected by the 2020 Reclassification Rule and EPA also identified source categories likely to be affected by the 2020 Reclassification Rule and
estimated potential changes in emissions. EPA concluded that while HAP emissions from 65 estimated potential changes in emissions. EPA concluded that while HAP emissions from 65
source categories would not change as a result of the 2020 Reclassification Rule, “approximately source categories would not change as a result of the 2020 Reclassification Rule, “approximately
130 facilities in seven source categories could increase emissions if they were to reclassify and 130 facilities in seven source categories could increase emissions if they were to reclassify and
were allowed to reduce operation of adjustable add-on controls.”were allowed to reduce operation of adjustable add-on controls.”~~113~~118 EPA estimated that EPA estimated that
nationwide, the potential HAPs emissions increase could range from about 900 tons per year to nationwide, the potential HAPs emissions increase could range from about 900 tons per year to
1,260 tons per year.1,260 tons per year.~~114~~119 EPA considered alternative scenarios, one of which estimated that EPA considered alternative scenarios, one of which estimated that
emissions could decrease nationwide by about 180 tons per year.emissions could decrease nationwide by about 180 tons per year.~~115~~120
Congress may consider whether CAA Section 112 provides EPA adequate authority to incentivize Congress may consider whether CAA Section 112 provides EPA adequate authority to incentivize
pollution prevention while also limiting cumulative HAP emissions. The act requires EPA to pollution prevention while also limiting cumulative HAP emissions. The act requires EPA to
establish technology-based emission limits (MACT) for major sources of HAPs. Under EPA’s establish technology-based emission limits (MACT) for major sources of HAPs. Under EPA’s
current interpretation of CAA Section 112, sources may change their classification after meeting current interpretation of CAA Section 112, sources may change their classification after meeting
conditions to limit HAPs below major source thresholds. While the 2020 Reclassification Rule conditions to limit HAPs below major source thresholds. While the 2020 Reclassification Rule
may provide sources an incentive to reduce HAPs below the major source thresholds, it is unclear may provide sources an incentive to reduce HAPs below the major source thresholds, it is unclear
whether actual emissions will decrease at each source that reclassifies as an area source. It is whether actual emissions will decrease at each source that reclassifies as an area source. It is
difficult to ascertain how the 2020 Reclassification Rule may affect emissions because the difficult to ascertain how the 2020 Reclassification Rule may affect emissions because the
reclassification is voluntary and due to the structure of MACT emission standards. MACT reclassification is voluntary and due to the structure of MACT emission standards. MACT
standards generally do not limit emissions to a fixed level, which makes it challenging to standards generally do not limit emissions to a fixed level, which makes it challenging to
determine how emissions from a particular source may change under a different standard.determine how emissions from a particular source may change under a different standard.~~116~~
~~Notwithstanding the various uncertainties, EPA estimated that, under certain assumptions, HAP~~
~~emissions could increase from about 130 facilities as a result of the 2020 Reclassification Rule.~~
~~Congress may consider the health and environmental implications of this potential outcome.117~~
~~Among other things, Congress may consider how these potential HAP increases contribute to~~
~~cumulative exposures in communities with disproportionate environmental burdens.~~
~~In addition, Congress may consider other impacts of the rule, such as the potential compliance~~
~~cost savings. EPA considered three categories of potential costs: (1) costs for major sources to~~
~~apply for reclassification, (2) costs for air pollution control agencies to process these applications,~~
~~and (3) compliance cost savings for a facility to meet area source standards compared to major~~
~~source standards. EPA’s illustrative analysis estimated a net annual cost savings across these three~~
~~cost categories when compared to a world with the OIAI policy.118 For example, EPA’s primary~~

~~112 2020 Reclassification Rule, p. 73880.~~
~~113~~121 115 For example, see Harvard Environmental & Energy Law Program, “Once In Always In Guidance for Major Sources Under the Clean Air Act,” https://eelp.law.harvard.edu/2018/02/once-in-always-in-guidance-for-major-sources-under-the-clean-air-act/. 116 Letter from Michael S. Bandrowski, Air Toxics Chief, EPA Region IX, to David Cozzie, Group Leader, EPA Office of Air Quality Planning and Standards, December 13, 2005, p. 3, see EPA Docket ID EPA-HQ-OAR-2004-0094-0151. 117 2020 Reclassification Rule, p. 73880. 118 EPA, “Final Rule: Reclassification of Major Sources as Area Sources Under Section 112 of the Clean Air Act,” fact EPA, “Final Rule: Reclassification of Major Sources as Area Sources Under Section 112 of the Clean Air Act,” fact
sheet, updated October 7, 2020, https://www.epa.gov/stationary-sources-air-pollution/documentation-reclassification-sheet, updated October 7, 2020, https://www.epa.gov/stationary-sources-air-pollution/documentation-reclassification-
major-sources-area-sources-under. Hereinafter, “Reclassification Fact Sheet.” major-sources-area-sources-under. Hereinafter, “Reclassification Fact Sheet.”
~~114~~119 Reclassification Fact Sheet. Reclassification Fact Sheet.
~~115~~120 Reclassification Fact Sheet. Reclassification Fact Sheet.
~~116~~121 MACT standards are generally expressed in terms of percent reduction, mass of emissions per mass production, or MACT standards are generally expressed in terms of percent reduction, mass of emissions per mass production, or
other similar format. Emissions from major sources may change over time based on various factors, such as changes in other similar format. Emissions from major sources may change over time based on various factors, such as changes in
production levels. See Letter from William L. Wehrum, Acting Assistant Administrator, to the Honorable John D. production levels. See Letter from William L. Wehrum, Acting Assistant Administrator, to the Honorable John D.
Dingell, Chairman, House Committee on Energy and Commerce, March 30, 2007; see EPA Docket ID EPA-HQ-OAR-Dingell, Chairman, House Committee on Energy and Commerce, March 30, 2007; see EPA Docket ID EPA-HQ-OAR-
2004-0094-0106. 2004-0094-0106.
~~117 EPA assessed rulemaking’s potential impact on tribal and environmental justice communities. See 2020~~
~~Reclassification Rule, p. 73882.~~
~~118 Memorandum from Eastern Research Group, Inc., to EPA, “Documentation of the Compliance Cost Savings~~
~~Analysis for the Rule ‘Reclassification of Major Sources as Area Sources Under Section 112 of the Clean Air Act,’”~~
~~August 2020, https://www.epa.gov/sites/production/files/2020-10/documents/mm2a_final_cost_analysis_tsm.pdf.~~
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Congressional Research Service 19 Clean Air Act Issues in the 117th Congress Notwithstanding the various uncertainties, EPA estimated that, under certain assumptions, HAP emissions could increase from about 130 facilities as a result of the 2020 Reclassification Rule. Congress may consider the health and environmental implications of this potential outcome.122 Among other things, Congress may consider how these potential HAP increases contribute to cumulative exposures in communities with disproportionate environmental burdens. In addition, Congress may consider other impacts of the rule, such as the potential compliance cost savings. EPA considered three categories of potential costs: (1) costs for major sources to apply for reclassification, (2) costs for air pollution control agencies to process these applications, and (3) compliance cost savings for a facility to meet area source standards compared to major source standards. EPA’s illustrative analysis estimated a net annual cost savings across these three cost categories when compared to a world with the OIAI policy.123 For example, EPA’s primary analytical scenario estimated $16.1 million in compliance costs in the first year and $90.6 million analytical scenario estimated $16.1 million in compliance costs in the first year and $90.6 million
in compliance cost savings in subsequent years.in compliance cost savings in subsequent years.~~119~~124
New Source Review Permits
Congress may continue to conduct oversight of New Source Review, a CAA preconstruction Congress may continue to conduct oversight of New Source Review, a CAA preconstruction
permitting program intended to ensure that new and modified stationary sources of air pollution permitting program intended to ensure that new and modified stationary sources of air pollution
do not significantly degrade air quality. The NSR program generally requires emission limits do not significantly degrade air quality. The NSR program generally requires emission limits
based on modern pollution controls when new facilities are built or when existing facilities make based on modern pollution controls when new facilities are built or when existing facilities make
a change that increases emissions above specified thresholds. Owners or operators must obtain an a change that increases emissions above specified thresholds. Owners or operators must obtain an
NSR permit before the construction or modification begins.NSR permit before the construction or modification begins.~~120~~125 Historically, NSR applicability Historically, NSR applicability
determinations have been contentious and extensively litigated.determinations have been contentious and extensively litigated.~~121~~126
Stakeholder views on NSR are often long-standing and divergent. Some stakeholders view NSR Stakeholder views on NSR are often long-standing and divergent. Some stakeholders view NSR
as essential to maintaining air quality, noting that because of its requirements for pollution control as essential to maintaining air quality, noting that because of its requirements for pollution control
strategies, the program “yields overall reductions in pollution even as facilities expand strategies, the program “yields overall reductions in pollution even as facilities expand
production.”production.”~~122~~127 Other stakeholders have described NSR as outdated and an impediment to Other stakeholders have described NSR as outdated and an impediment to
economic growth, stating that the complexities and costs of the NSR permitting process economic growth, stating that the complexities and costs of the NSR permitting process
discourage pollution-control projects.discourage pollution-control projects.~~123~~
~~Over time, EPA has issued guidance and explored rulemakings meant to improve or clarify~~
~~program implementation. In 2017, EPA announced an NSR reform initiative, which included~~
~~revisiting some NSR proposals from prior Administrations that were not finalized.124 Since 2017,~~
~~EPA has issued various guidance memoranda and taken regulatory actions under this initiative.125~~
~~These actions have centered on NSR applicability and enforcement. For example, EPA guidance~~
~~has discussed how to determine what counts as a source for NSR purposes;126 how to account for~~

~~Hereinafter, “EPA Reclassification Cost Analysis.”~~
~~119~~128 122 EPA assessed rulemaking’s potential impact on tribal and environmental justice communities. See 2020 Reclassification Rule, p. 73882. 123 Memorandum from Eastern Research Group, Inc., to EPA, “Documentation of the Compliance Cost Savings Analysis for the Rule ‘Reclassification of Major Sources as Area Sources Under Section 112 of the Clean Air Act,’” August 2020, https://www.epa.gov/sites/production/files/2020-10/documents/mm2a_final_cost_analysis_tsm.pdf. Hereinafter, “EPA Reclassification Cost Analysis.” 124 EPA’s primary illustrative scenario estimated the compliance costs and compliance cost savings for 2,567 facilities EPA’s primary illustrative scenario estimated the compliance costs and compliance cost savings for 2,567 facilities
to reclassify. The 2,567 facilities represent roughly one-third of the 7,183 sources with emissions that are already below to reclassify. The 2,567 facilities represent roughly one-third of the 7,183 sources with emissions that are already below
the major source threshold. See both EPA Reclassification Cost Analysis and Reclassification Fact Sheet. the major source threshold. See both EPA Reclassification Cost Analysis and Reclassification Fact Sheet.
~~120~~125 The NSR permit is a legal document that establishes site-specific requirements for the source, detailing approved The NSR permit is a legal document that establishes site-specific requirements for the source, detailing approved
types of construction, emission limits during operation, monitoring and reporting requirements, and other construction types of construction, emission limits during operation, monitoring and reporting requirements, and other construction
and operating conditions. State and local permitting agencies generally implement NSR and issue the permits. EPA and operating conditions. State and local permitting agencies generally implement NSR and issue the permits. EPA
generally oversees the state’s implementation. generally oversees the state’s implementation.
~~121~~126 For discussion of key legal decisions on NSR, see CRS Report R43699, For discussion of key legal decisions on NSR, see CRS Report R43699, Key Historical Court Decisions Shaping
EPA’s Program Under the Clean Air Act, by Linda Tsang. , by Linda Tsang.
~~122~~127 Harvard Environmental and Energy Law Program, Harvard Environmental and Energy Law Program, EPA’s Attack on New Source Review and Other Air Quality
Protection Tools, November 1, 2019, http://eelp.law.harvard.edu/wp-content/uploads/NSR-paper-EELP.pdf. , November 1, 2019, http://eelp.law.harvard.edu/wp-content/uploads/NSR-paper-EELP.pdf.
~~123~~128 Art Fraas, John Graham, and Jeff Holmstead, “EPA’s New Source Review Program: Time for Reform?” Art Fraas, John Graham, and Jeff Holmstead, “EPA’s New Source Review Program: Time for Reform?”
Environmental Law Reporter, vol. 47, no. 1, (2017). Also available at https://www.rff.org/publications/journal-articles/, vol. 47, no. 1, (2017). Also available at https://www.rff.org/publications/journal-articles/
Congressional Research Service 20 Clean Air Act Issues in the 117th Congress Over time, EPA has issued guidance and explored rulemakings meant to improve or clarify program implementation. In 2017, EPA announced an NSR reform initiative, which included revisiting some NSR proposals from prior Administrations that were not finalized.129 Since 2017, EPA has issued various guidance memoranda and taken regulatory actions under this initiative.130 These actions have centered on NSR applicability and enforcement. For example, EPA guidance has discussed how to determine what counts as a source for NSR purposes;131 how to account for air emissions in determining whether NSR applies;132 and circumstances under which EPA will not “second-guess” a facility’s projections of emissions that will result from a modification.133 The Biden Administration may review the Trump Administration’s NSR actions if EPA determines that those actions fall within the scope of its reviews under E.O. 13990.134 In October 2021, EPA reported plans to undertake a rulemaking process to consider revisions to NSR regulations,135 specifically the November 2020 “project emissions accounting” rule, which had revised the NSR applicability regulations.136 epas-new-source-review-program-time-for-reform/. 129~~epas-new-source-review-program-time-for-reform/.~~
~~124~~ U.S. Environmental Protection Agency, U.S. Environmental Protection Agency, Final Report on Review of Agency Actions that Potentially Burden the Safe,
Efficient Development of Domestic Energy Resources Under Executive Order 13783, October 2017, , October 2017,
https://www.epa.gov/sites/production/files/2017-10/documents/eo-13783-final-report-10-25-2017.pdf. EPA has https://www.epa.gov/sites/production/files/2017-10/documents/eo-13783-final-report-10-25-2017.pdf. EPA has
previously explored rulemakings intended to improve or clarify NSR; see selection of rulemakings that EPA identifies previously explored rulemakings intended to improve or clarify NSR; see selection of rulemakings that EPA identifies
under “NRS Reform” at https://www.epa.gov/nsr/nsr-regulatory-actions#nsrreform. under “NRS Reform” at https://www.epa.gov/nsr/nsr-regulatory-actions#nsrreform.
~~125~~130 For a list of EPA guidance memoranda related to NSR, see U.S. Environmental Protection Agency, For a list of EPA guidance memoranda related to NSR, see U.S. Environmental Protection Agency, New Source
Review Policy and Guidance Document Index, https://www.epa.gov/nsr/new-source-review-policy-and-guidance-, https://www.epa.gov/nsr/new-source-review-policy-and-guidance-
document-index. For regulatory actions that EPA identifies as part of “NSR Reform,” see https://www.epa.gov/nsr/nsr-document-index. For regulatory actions that EPA identifies as part of “NSR Reform,” see https://www.epa.gov/nsr/nsr-
regulatory-actions#nsrreform. regulatory-actions#nsrreform.
~~126~~131 For example, EPA published a guidance memorandum to clarify when it considers industrial facilities to be under For example, EPA published a guidance memorandum to clarify when it considers industrial facilities to be under
“common control” and therefore count as one source for NSR purposes. See Memorandum from William L. Wehrum, “common control” and therefore count as one source for NSR purposes. See Memorandum from William L. Wehrum,
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~~air emissions in determining whether NSR applies;127 and circumstances under which EPA will~~
~~not “second-guess” a facility’s projections of emissions that will result from a modification.128~~
~~The Biden Administration may review the Trump Administration’s NSR actions if EPA~~
~~determines that those actions fall within the scope of its reviews under E.O. 13990.129 In addition,~~
~~at least one NSR action may be eligible for review by Congress under the CRA. Known as the~~
~~“project emissions accounting” rule, EPA revised the NSR applicability regulations in November~~
~~2020.130~~
~~Stakeholders that view NSR as essential to maintaining air quality have voiced concern that these~~
~~NSR actions would be expected to reduce EPA’s oversight and create a more lenient NSR regime,~~
~~thereby allowing increased emissions of harmful pollutants from U.S. industrial facilities.131~~
~~Stakeholders critical of NSR generally have expressed support for some of EPA’s recent NSR~~
~~actions, citing, for example, greater regulatory certainty and incentives for projects that emit less~~
~~pollution.132~~

Assistant Administrator, EPA, to Patrick McDonnell, Secretary of the Pennsylvania Department of Environmental Assistant Administrator, EPA, to Patrick McDonnell, Secretary of the Pennsylvania Department of Environmental
Protection, April 30, 2018, https://www.epa.gov/sites/production/files/2018-05/documents/meadowbrook_2018.pdf. Protection, April 30, 2018, https://www.epa.gov/sites/production/files/2018-05/documents/meadowbrook_2018.pdf.
EPA’s 2019 guidance regarding the term EPA’s 2019 guidance regarding the term adjacent is another example; it discusses whether sources located on is another example; it discusses whether sources located on
“adjacent” properties should be combined for purposes of NSR; see Memorandum from Anne L. Idsal, Acting “adjacent” properties should be combined for purposes of NSR; see Memorandum from Anne L. Idsal, Acting
Assistant Administrator, EPA, to EPA Regional Administrators, November 26, 2019, https://www.epa.gov/sites/Assistant Administrator, EPA, to EPA Regional Administrators, November 26, 2019, https://www.epa.gov/sites/
production/files/2019-11/documents/adjacent_guidance.pdf. production/files/2019-11/documents/adjacent_guidance.pdf.
~~127~~132 For example, EPA’s March 2018 “Project Emissions Accounting” memorandum states that a facility owner would For example, EPA’s March 2018 “Project Emissions Accounting” memorandum states that a facility owner would
consider both emission increases and emission decreases, provided they are from a single project, in the first step of a consider both emission increases and emission decreases, provided they are from a single project, in the first step of a
multistep process to determine whether emissions from the proposed project would trigger NSR; see Memorandum multistep process to determine whether emissions from the proposed project would trigger NSR; see Memorandum
from Honorable E. Scott Pruitt, EPA Administrator, to EPA Regional Administrators, March 13, 2018, from Honorable E. Scott Pruitt, EPA Administrator, to EPA Regional Administrators, March 13, 2018,
https://www.epa.gov/sites/production/files/2018-03/documents/nsr_memo_03-13-2018.pdf. In 2020, EPA finalized a https://www.epa.gov/sites/production/files/2018-03/documents/nsr_memo_03-13-2018.pdf. In 2020, EPA finalized a
rule to revise the NSR applicability regulations to “make it clear that both emissions increases and emissions decreases rule to revise the NSR applicability regulations to “make it clear that both emissions increases and emissions decreases
that result from a given proposed project are to be considered at Step 1 of the NSR major modification applicability that result from a given proposed project are to be considered at Step 1 of the NSR major modification applicability
test.” See EPA, “Prevention of Significant Deterioration (PSD) and Nonattainment New Source Review (NNSR): test.” See EPA, “Prevention of Significant Deterioration (PSD) and Nonattainment New Source Review (NNSR):
Project Emissions Accounting,” 85Project Emissions Accounting,” 85 Federal Register 74890, November 24, 2020. 74890, November 24, 2020.
~~128~~ 133 Letter from Honorable E. Scott Pruitt, EPA Administrator, to EPA Regional Administrators, December 7, 2017, Letter from Honorable E. Scott Pruitt, EPA Administrator, to EPA Regional Administrators, December 7, 2017,
https://www.epa.gov/sites/production/files/2017-12/documents/policy_memo.12.7.17.pdf. https://www.epa.gov/sites/production/files/2017-12/documents/policy_memo.12.7.17.pdf.
~~129~~134 E.O. 13990 requires federal agencies to review “all existing regulations, orders, guidance documents, policies, and E.O. 13990 requires federal agencies to review “all existing regulations, orders, guidance documents, policies, and
any other similar agency actions” taken during the Trump Administration and to consider “suspending, revising, or any other similar agency actions” taken during the Trump Administration and to consider “suspending, revising, or
rescinding” agency actions that are deemed inconsistent with the order’s stated policy concerning protection of public rescinding” agency actions that are deemed inconsistent with the order’s stated policy concerning protection of public
health and the environment and addressing climate change. health and the environment and addressing climate change.
~~130 EPA~~135 Letter from Michael S. Regan, EPA Administrator, to Sanjay Narayan, Acting Director, Sierra Club Environmental Law Program, October 12, 2021, https://www.epa.gov/system/files/documents/2021-10/oar-21-000-6429-narayan_0.pdf 136 The 2020 rule sought to “make it clear that both emissions increases and emissions decreases that result from a given sought to “make it clear that both emissions increases and emissions decreases that result from a given
proposed project are to be considered at Step 1 of the NSR major modification applicability test.” See EPA, proposed project are to be considered at Step 1 of the NSR major modification applicability test.” See EPA,
“Prevention of Significant Deterioration (PSD) and Nonattainment New Source Review (NNSR): Project Emissions “Prevention of Significant Deterioration (PSD) and Nonattainment New Source Review (NNSR): Project Emissions
Accounting,” 85Accounting,” 85 Federal Register 74890, November 24, 2020. 74890, November 24, 2020.
~~131 Harvard Environmental and Energy Law Program, Regulatory Rollback: New Source Review, December 11, 2018~~
~~(updated February 2020), https://eelp.law.harvard.edu/2018/12/new-source-review/.~~
~~132 For example, a letter signed by 12 industry associations stated that EPA’s Project Emissions Accounting (PEA)~~
~~proposal (84 Federal Register 39244, August 9, 2019) to “codify the PEA interpretation is reasonable, consistent with~~
~~the Clean Air Act and sound policy, and important to provide regulatory certainty to enable and even incentivize~~
~~projects to reduce emissions and drive productive capacity”; see https://www.regulations.gov/document?D=EPA-HQ-~~
~~OAR-2018-0048-0081.~~
~~Congressional Research Service~~

21

~~Clean Air Act Issues in the 117th Congress~~

Congressional Research Service 21 Clean Air Act Issues in the 117th Congress Stakeholders that view NSR as essential to maintaining air quality have voiced concern that these NSR actions would be expected to reduce EPA’s oversight and create a more lenient NSR regime, thereby allowing increased emissions of harmful pollutants from U.S. industrial facilities.137 Stakeholders critical of NSR generally have expressed support for some of EPA’s recent NSR actions, citing, for example, greater regulatory certainty and incentives for projects that emit less pollution.138 Congress may conduct oversight of the NSR program or consider legislative proposals to modify Congress may conduct oversight of the NSR program or consider legislative proposals to modify
it. Congress may also use the appropriations process to support or limit EPA spending on specific it. Congress may also use the appropriations process to support or limit EPA spending on specific
activities. Congress has previously considered legislative proposals to modify NSR.activities. Congress has previously considered legislative proposals to modify NSR.~~133~~139 For For
example, in the 116th Congress, S. 2662 and H.R. 172 would have amended the CAA definition of example, in the 116th Congress, S. 2662 and H.R. 172 would have amended the CAA definition of
modification, a key term in determining NSR applicability. The CAA broadly , a key term in determining NSR applicability. The CAA broadly
defines defines modification as “any” physical or operational change in a stationary source “that increases as “any” physical or operational change in a stationary source “that increases
the emissions of any air pollutant or results in the emission of any air pollutant not previously the emissions of any air pollutant or results in the emission of any air pollutant not previously
emitted.”emitted.”~~134~~140 S. 2662 and H.R. 172 would have, among other things, allowed emissions increases S. 2662 and H.R. 172 would have, among other things, allowed emissions increases
from modifications to be calculated on an hourly basis rather than an annual basis. The bills from modifications to be calculated on an hourly basis rather than an annual basis. The bills
would also have excluded certain projects, such as those designed to reduce the amount of any air would also have excluded certain projects, such as those designed to reduce the amount of any air
pollutant emitted or “to restore, maintain, or improve the reliability of operations at, or the safety pollutant emitted or “to restore, maintain, or improve the reliability of operations at, or the safety
of, the source” from the definition of a modification. of, the source” from the definition of a modification.

Author Information Kate C. Shouse Analyst in Environmental Policy 137 Harvard Environmental and Energy Law Program, Regulatory Rollback: New Source Review, December 11, 2018 (updated February 2020), https://eelp.law.harvard.edu/2018/12/new-source-review/. 138 For example, a letter signed by 12 industry associations stated that EPA’s Project Emissions Accounting (PEA) proposal (84 Federal Register 39244, August 9, 2019) to “codify the PEA interpretation is reasonable, consistent with the Clean Air Act and sound policy, and important to provide regulatory certainty to enable and even incentivize projects to reduce emissions and drive productive capacity”; see https://www.regulations.gov/document?D=EPA-HQ-OAR-2018-0048-0081. 139 ~~Author Information~~

~~Kate C. Shouse~~

~~Analyst in Environmental Policy~~

~~Disclaimer~~
~~This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan~~
~~shared staff to congressional committees and Members of Congress. It operates solely at the behest of and~~
~~under the direction of Congress. Information in a CRS Report should not be relied upon for purposes other~~
~~than public understanding of information that has been provided by CRS to Members of Congress in~~
~~connection with CRS’s institutional role. CRS Reports, as a work of the United States Government, are not~~
~~subject to copyright protection in the United States. Any CRS Report may be reproduced and distributed in~~
~~its entirety without permission from CRS. However, as a CRS Report may include copyrighted images or~~
~~material from a third party, you may need to obtain the permission of the copyright holder if you wish to~~
~~copy or otherwise use copyrighted material.~~

~~133~~ See U.S. Congress, Senate Committee on Environment and Public Works, See U.S. Congress, Senate Committee on Environment and Public Works, Hearing on S. 2662, The Growing
American Innovation (GAIN) Act, 116th Cong., 1st sess., November 6, 2019, https://www.epw.senate.gov/public/, 116th Cong., 1st sess., November 6, 2019, https://www.epw.senate.gov/public/
index.cfm/hearings?ID=9D9A2920-4591-4532-9D64-AE9F98437707. See also (1) U.S. Congress, House Committee index.cfm/hearings?ID=9D9A2920-4591-4532-9D64-AE9F98437707. See also (1) U.S. Congress, House Committee
on Energy and Commerce, Subcommittee on Environment, on Energy and Commerce, Subcommittee on Environment, New Source Review Permitting Challenges for
Manufacturing and Infrastructure, 115th Cong., 2nd sess., February 14, 2018, https://energycommerce.house.gov/, 115th Cong., 2nd sess., February 14, 2018, https://energycommerce.house.gov/
hearings/new-source-review-permitting-challenges-manufacturing-infrastructure/; and (2) U.S. Congress, House hearings/new-source-review-permitting-challenges-manufacturing-infrastructure/; and (2) U.S. Congress, House
Committee on Energy and Commerce, Subcommittee on Environment, Committee on Energy and Commerce, Subcommittee on Environment, Legislation Addressing New Source Review
Permitting Reform, 115th Cong., 2nd sess., May 16, 2018, https://energycommerce.house.gov/committee-activity/, 115th Cong., 2nd sess., May 16, 2018, https://energycommerce.house.gov/committee-activity/
hearings/hearing-on-legislation-addressing-new-source-review-permitting-reform. hearings/hearing-on-legislation-addressing-new-source-review-permitting-reform.
~~134~~140 CAA §111(a)(4), 42 U.S.C. §7411(a)(4), defines CAA §111(a)(4), 42 U.S.C. §7411(a)(4), defines modification for purposes of the NSPS section of the CAA. CAA for purposes of the NSPS section of the CAA. CAA
§169(2)(C), 42 U.S.C. §7479(2)(C), specifies that that definition applies as well within the Prevention of Significant §169(2)(C), 42 U.S.C. §7479(2)(C), specifies that that definition applies as well within the Prevention of Significant
Deterioration portion of the statute. EPA and state air pollution control agencies have interpreted this definition to Deterioration portion of the statute. EPA and state air pollution control agencies have interpreted this definition to
implement NSR through regulations and policy guidance. EPA’s interpretation of implement NSR through regulations and policy guidance. EPA’s interpretation of modification under the NSR program under the NSR program
has been subject to various legal challenges. has been subject to various legal challenges.
Congressional Research Service Congressional Research Service
22 Clean Air Act Issues in the 117th Congress Disclaimer This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan shared staff to congressional committees and Members of Congress. It operates solely at the behest of and under the direction of Congress. Information in a CRS Report should not be relied upon for purposes other than public understanding of information that has been provided by CRS to Members of Congress in connection with CRS’s institutional role. CRS Reports, as a work of the United States Government, are not subject to copyright protection in the United States. Any CRS Report may be reproduced and distributed in its entirety without permission from CRS. However, as a CRS Report may include copyrighted images or material from a third party, you may need to obtain the permission of the copyright holder if you wish to copy or otherwise use copyrighted material. Congressional Research Service R46684 · VERSION 3 · UPDATED 23 ~~R46684 · VERSION 1 · NEW~~
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