Clean Air Act: A Summary of the Act and Its Major Requirements

January 3, 2003 – September 13, 2022 RL30853

Clean Air Act: A Summary of the Act and
Its Major Requirements
Updated September 13, 2022
Congressional Research Service
https://crsreports.congress.gov
RL30853

Clean Air Act: A Summary of the Act and Its Major Requirements

Summary
This report summarizes the Clean Air Act and its major regulatory requirements. The principal
statute addressing air quality concerns, the Clean Air Act was first enacted in 1955, with major
revisions in 1970, 1977, and 1990. The act
 requires EPA to set health-based standards for ambient air quality;
 sets deadlines for the achievement of those standards by state and local
governments;
 requires EPA to set national emission standards for large or ubiquitous sources of
air pollution, including motor vehicles, power plants, and other industrial
sources;
 mandates emission controls for sources of 187 hazardous air pollutants;
 establishes a cap-and-trade program to limit acid rain;
 requires the prevention of significant deterioration of air quality in areas with
clean air;
 requires a program to restore visibility impaired by regional haze in national
parks and wilderness areas; and
 implements the Montreal Protocol to phase out most ozone-depleting chemicals.
This report describes the act’s major provisions and provides tables listing all major amendments,
with the year of enactment and Public Law number, and cross-referencing sections of the act with
the major U.S. Code sections of the codified statute.
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Clean Air Act: A Summary of the Act and Its Major Requirements

Introduction
The authorities and responsibilities of the U.S. Environmental Protection Agency (EPA) derive
primarily from a dozen major environmental statutes. This report provides a concise summary of
one of those statutes, the Clean Air Act. It provides a very brief history of federal involvement in
air quality regulation and of the provisions added by legislation in 1970, 1977, and 1990; it
explains major authorities contained in the act; it defines key terms; and it lists references for
more detailed information on the act and its implementation.
While this report attempts to present the essence of the act, it is necessarily incomplete. Many
details and secondary provisions are omitted. In addition, the report describes the statute largely
without discussing its implementation. Statutory deadlines to control emissions and achieve
particular mandates have often been missed as a result of delayed standard-setting by EPA,
delayed action on implementation by states and local governments, or law suits brought by
interested parties. Other CRS products discuss implementation concerns and current issues.
Overview
The Clean Air Act, 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. It requires EPA to establish
minimum national standards for air quality, and assigns primary responsibility to the states to
assure compliance with the standards. Areas not meeting the standards, referred to as
“nonattainment areas,” are required to implement specified air pollution control measures. The
act establishes federal standards for mobile sources of air pollution and their fuels and for sources
of 187 hazardous air pollutants, and it establishes a cap-and-trade program for the emissions that
cause acid rain. It establishes a comprehensive permit system for all major sources of air
pollution. It also addresses the prevention of pollution in areas with clean air and protection of the
stratospheric ozone layer.
Like many other programs administered by the EPA, federal efforts to control air pollution have
gone through several phases, beginning with information collection, research, and technical
assistance, before being strengthened to establish federal standards and enforcement. Federal
legislation addressing air pollution was first passed in 1955, prior to which air pollution was the
exclusive responsibility of state and local levels of government.
The federal role was strengthened in subsequent amendments, notably the Clean Air Act
Amendments of 1970, 1977, and 1990. The 1970 amendments established the procedures under
which EPA sets national standards for ambient air quality, required a 90% reduction in emissions
from new automobiles by 1975, established a program to require the best available control
technology at major new sources of air pollution, established a program to regulate air toxics, and
greatly strengthened federal enforcement authority. The 1977 amendments adjusted the auto
emission standards, extended deadlines for the attainment of air quality standards, and added the
Prevention of Significant Deterioration program to protect air cleaner than national standards.
Table 1. Clean Air Act and Amendments
(codified generally as 42 U.S.C. 7401-7671)
Year
Act
Public Law Number
1955
Air Pol ution Control Act
P.L. 84-159
1959
Reauthorization
P.L. 86-353
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Year
Act
Public Law Number
1960
Motor vehicle exhaust study
P.L. 86-493
1963
Clean Air Act Amendments
P.L. 88-206
1965
Motor Vehicle Air Pol ution Control Act
P.L. 89-272, Title I
1966
Clean Air Act Amendments of 1966
P.L. 89-675
1967
Air Quality Act of 1967
P.L. 90-148
National Air Emission Standards Act
1970
Clean Air Act Amendments of 1970
P.L. 91-604
1973
Reauthorization
P.L. 93-13
1974
Energy Supply and Environmental Coordination Act of 1974
P.L. 93-319
1977
Clean Air Act Amendments of 1977
P.L. 95-95
1980
Acid Precipitation Act of 1980
P.L. 96-294, Title VII
1981
Steel Industry Compliance Extension Act of 1981
P.L. 97-23
1987
Clean Air Act 8-month Extension
P.L. 100-202
1990
Clean Air Act Amendments of 1990
P.L. 101-549
1991
Technical correction to list of hazardous air pol utants
P.L. 102-187
1995-96 Relatively minor laws amending the act
P.L. 104-6, 59, 70, 260
1998
Amended §604 re methyl bromide
P.L. 105-277, §764
1998
Border Smog Reduction Act of 1998
P.L. 105-286
1999
Chemical Safety Information, Site Security and Fuels
P.L. 106-40
Regulatory Relief Act
2004
Amendments to §209 re small engines
P.L. 108-199, Division G, Title IV, §428
2005
Energy Policy Act of 2005 (amended §211 re fuels)
P.L. 109-58
2007
Energy Independence and Security Act of 2007 (amended
P.L. 110-140
§211 re fuels)
2011
Amendments re Alaskan Outer Continental Shelf sources and P.L. 112-74, §432, and P.L. 112-81,
ozone depleting substances
§320
2014
Amendment to §207 re motor vehicle dealer certification
P.L. 113-109
2015
Amendment regarding special y produced motor vehicles
P.L. 114-94, §24405
2020
Amendment to §103(g), re research related to direct air
P.L. 116-260, Division S, §102(b)
capture of carbon dioxide and carbon storage in deep saline
formations.
2022
Inflation Reduction Act (amended Title I, Part A by adding
P.L. 117-169, Title VI
§§132-138 re funding and programming for various air
pol ution and greenhouse gas emission programs.
Changes to the act in 1990 included provisions to (1) classify most nonattainment areas according
to the extent to which they exceed the standard, tailoring deadlines, planning, and controls to each
area’s status; (2) tighten auto and other mobile source emission standards; (3) require
reformulated and alternative fuels in the most polluted areas; (4) revise the air toxics section,
establishing a new program of technology-based standards and addressing the problem of sudden,
catastrophic releases of air toxics; (5) establish an acid rain control program, with a marketable
allowance scheme to provide flexibility in implementation; (6) require a state-run permit program
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for the operation of major sources of air pollutants; (7) implement the Montreal Protocol to phase
out most ozone-depleting chemicals; and (8) update the enforcement provisions so that they
parallel those in other pollution control acts, including authority for EPA to assess administrative
penalties.
The 1990 amendments also authorized appropriations for clean air programs through FY1998.
The act has not been reauthorized since then. House rules require enactment of an authorization
before an appropriation bill can be considered; but this requirement can be waived and frequently
has been. Thus, while authorization of appropriations in the Clean Air Act (and most other
environmental statutes) has expired, programs have continued and have been funded. The act’s
other legal authorities, to issue and enforce regulations, are, for the most part, permanent and are
not affected by the lack of authorization.
The remainder of this report describes major programs required by the act, with an emphasis on
the changes established by the 1990 amendments.
National Ambient Air Quality Standards
In section 109, the act requires EPA to establish National Ambient Air Quality Standards
(NAAQS) for air pollutants that endanger public health or welfare,1 in the administrator’s
judgment, and whose presence in ambient air results from numerous or diverse sources. The
NAAQS must be designed to protect public health with an adequate margin of safety and to
protect public welfare from any known or anticipated adverse effects. Using this authority, EPA
has promulgated NAAQS for six air pollutants or groups of pollutants: sulfur dioxide (SO2),
particulate matter (PM2.5 and PM10), nitrogen dioxide (NO2), carbon monoxide (CO), ozone,2 and
lead. The act requires EPA to review the scientific data upon which the standards are based every
five years, and revise the standards, if necessary. More often than not, EPA has taken more than
five years in reviewing the standards, but the establishment of a deadline has allowed interested
parties to force review of the standards by filing suit.
Originally, the act required that the NAAQS be attained by 1977 at the latest, but the states
experienced widespread difficulty in complying with this deadline. As a result, the deadlines for
achieving NAAQS have been extended several times. Under the 1990 amendments, most areas
not in attainment with NAAQS must meet special compliance schedules, staggered according to
the severity of an area’s air pollution problem. The amendments also established specific
requirements for each nonattainment category, as described below.
State Implementation Plans
While the act authorizes EPA to set NAAQS, the states are responsible for establishing
procedures to attain and maintain the standards. Under Section 110 of the act, the states adopt
plans, known as State Implementation Plans (SIPs), and submit them to EPA to ensure that they
are adequate to meet statutory requirements.

1 Welfare is defined by the act to include effects on soils, water, crops, vegetation, manmade materials, animals,
wildlife, weather, visibility, and climate, damage to and deterioration of property, and hazards to transportation, as well
as effects on economic values and on personal comfort and well-being.
2 Unlike most other NAAQS pollutants, ozone is not directly emitted, but rather is formed in the atmosphere by the
interaction of volatile organic compounds (VOCs) and nitrogen oxides (NOx) in the presence of sunlight. The control
of ozone is, thus, based on regulating emissions of VOCs and NOx. Many particulates also form in the atmosphere after
transformation of precursor emissions.
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SIPs are based on emission inventories and computer models to determine whether air quality
violations will occur. If these data show that standards would be exceeded, the state must impose
additional controls on existing sources to ensure that emissions do not cause “exceedances” of the
standards. Proposed new and modified sources must obtain state construction permits in which
the applicant shows how the anticipated emissions will not exceed allowable limits. In
nonattainment areas, emissions from new or modified sources must also be offset by reductions in
emissions from existing sources.
The 1990 amendments require EPA to impose sanctions in areas which fail to submit a SIP, fail to
submit an adequate SIP, or fail to implement a SIP: unless the state corrects such failures, a 2-to-1
emissions offset for the construction of new polluting sources is imposed 18 months after
notification to the state, and a ban on most new federal highway grants is imposed 6 months later.
An additional ban on air quality grants is discretionary. Ultimately, a Federal Implementation
Plan may be imposed if the state fails to submit or implement an adequate SIP.
The amendments also require that, in nonattainment areas, no federal permits or financial
assistance may be granted for activities that do not “conform” to a SIP. This requirement can
cause a temporary suspension in funding for most new highway and transit projects if an area
fails to demonstrate that the emissions caused by such projects are consistent with attainment and
maintenance of ambient air quality standards. Demonstrating conformity of transportation plans
and SIPs is required in nonattainment areas whenever new plans are submitted.
Nonattainment Requirements
In a major departure from the prior law, the 1990 Clean Air Act Amendments grouped most
nonattainment areas into classifications based on the extent to which the NAAQS was exceeded,
and established specific pollution controls and attainment dates for each classification. These
requirements are described here as spelled out in Sections 181-193 of the act.3
Nonattainment areas are classified on the basis of a “design value,” which is derived from the
pollutant concentration (in parts per million or micrograms per cubic meter) recorded by air
quality monitoring devices. The design value for the one-hour ozone standard was the fourth
highest hourly reading measured during the most recent three-year period. Using these design
values, the act created five classes of ozone nonattainment, as shown in Table 2. Initially, only
Los Angeles fell into the “extreme” class, but 97 other areas were classified in one of the other
four ozone categories. The classification system and design values have since been adapted twice
as the ozone standard has been revised. Under the 2015 standard, there are 49 nonattainment
areas as of July 2022, all but 10 of which are classified as “marginal” or “moderate” (see Table
3).4 A simpler classification system established moderate and serious nonattainment areas for
carbon monoxide and particulate matter with correspondingly more stringent control
requirements for the more polluted class.

3 EPA modified the ozone standard, specified in the statute as 0.12 parts per million (ppm) averaged over a one-hour
period, to 0.08 ppm averaged over an eight-hour period, through regulations promulgated in July 1997. In April 2004,
the agency promulgated an implementation rule for the new eight-hour standard. Under this rule, the one-hour standard
was revoked as of June 15, 2005, and areas that had not yet attained it were converted to new classifications depending
on their eight-hour concentration of ozone. In general, the former one-hour nonattainment areas remain subject to the
controls specified for their one-hour category, but most areas were given additional time to attain the new standard. The
ozone standard was revised again in March 2008, to 0.075 ppm averaged over eight hours and in October 2015, to
0.070 ppm averaged over eight hours.
4 EPA, Green Book, 8-Hour Ozone (2015) Designated Area/State Information, data current as of July 31, 2022,
https://www3.epa.gov/airquality/greenbook/jbtc.html.
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Table 2. Statutory Ozone Nonattainment Classifications
Class
Marginal
Moderate
Serious
Severe
Extreme
Deadline
1993
1996
1999
2005-2007a
2010
Areasb
42 areas
32 areas
14 areas
9 areas
1 area
Design
0.121 ppm-
0.138 ppm-
0.160 ppm-
0.180 ppm-
≥0.280 ppm
Value
0.138 ppm
0.160 ppm
0.180 ppm
0.280 ppm
a. Areas with a 1988 design value between 0.190 and 0.280 ppm had 17 years to attain; others had 15 years.
b. Number of areas in each category as of the date of enactment.
As shown in Table 2, the statutory attainment deadlines for ozone nonattainment areas stretched
from 1993 to 2010, depending on the severity of the problem. Under the current eight-hour ozone
standard, shown in Table 3, these deadlines are changed to 2021 to 2038.
Table 3. Ozone Nonattainment Classifications, as of July 2022
Class
Marginal
Moderate
Serious
Severea
Extreme
Deadline
2021
2024
2027
2033-a
2038
Areasb
38 areas
1 areas
5 areas
3 areas
2 areas
Design
0.071 ppm-
0.081 ppm-
0.093 ppm-
0.105 ppm-
≥0.163 ppm
Valuec
0.081 ppm
0.093 ppm
0.105 ppm
0.163 ppm
a. Areas with a design value between 0.105 and 0.111 ppm have 15 years to attain (“Severe 15”). Areas with a
design value between 0.111 and 0.163 ppm have 17 years to attain (“Severe 17”); as of July 31, 2022, there
are not any Severe 17 areas with respect to the 2015 ozone standard.
b. Number of areas in each category as of July 2022.
c. Except for the Extreme classification, the design values for each classification range from the lower value
given up to, but not including, the higher value.
For carbon monoxide, the attainment date for moderate areas was December 31, 1995, and for
serious areas, December 31, 2000. Since 2010, there have been no carbon monoxide
nonattainment areas.
For particulate matter, the deadline for areas designated moderate nonattainment as of 1990 was
December 31, 1994; for those areas subsequently designated as moderate, the deadline is six
years after designation. For serious areas, the respective deadlines are December 31, 2001, or 10
years after designation.
Requirements for Ozone Nonattainment Areas
Although areas with more severe air pollution problems have a longer time to meet the standards,
more stringent control requirements are imposed in areas with worse pollution. A summary of the
primary ozone control requirements for each nonattainment category follows.
Marginal Areas
 Inventory emissions sources (to be updated every three years).
 Require 1.1 to 1 offsets (i.e., new major emission sources of volatile organic
compounds [VOCs] must reduce VOC emissions from existing facilities in the
area by 10% more than the emissions of the new facility).
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 Impose reasonably available control technology (RACT) on all major sources
emitting more than 100 tons per year for the nine industrial categories where EPA
had already issued control technique guidelines describing RACT prior to 1990.
Moderate Areas
 Meet all requirements for marginal areas.
 Impose a 15% reduction in VOC emissions in six years.
 Adopt a basic vehicle inspection and maintenance program.
 Impose RACT on all major sources emitting more than 100 tons per year for all
additional industrial categories where EPA will issue control technique guidelines
describing RACT.
 Require vapor recovery at gas stations selling more than 10,000 gallons per
month.
 Require 1.15 to 1 offsets.
Serious Areas
 Meet all requirements for moderate areas.
 Reduce definition of a major source of VOCs from emissions of 100 tons per
year to 50 tons per year for the purpose of imposing RACT.
 Reduce VOCs 3% annually for years 7 to 9 after the 15% reduction already
required by year 6.
 Improve monitoring, in order to obtain more comprehensive and representative
data on ozone pollution.
 Adopt an enhanced vehicle inspection and maintenance program.
 Require fleet vehicles to use clean alternative fuels.
 Adopt transportation control measures if the number of vehicle miles traveled in
the area is greater than expected.
 Require 1.2 to 1 offsets.
 Adopt contingency measures if the area does not meet required VOC reductions.
Severe Areas
 Meet all requirements for serious areas.
 Reduce definition of a major source of VOCs from emissions of 50 tons per year
to 25 tons per year for the purpose of imposing RACT.
 Adopt specified transportation control measures.
 Implement a reformulated gasoline program.
 Require 1.3 to 1 offsets.
 Impose $5,000 per ton penalties on major sources if the area does not meet
required reductions.
Extreme Areas
 Meet all requirements for severe areas.
 Reduce definition of a major source of VOCs from emissions of 25 tons per year
to 10 tons per year for the purpose of imposing RACT.
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 Require clean fuels or advanced control technology for boilers emitting more
than 25 tons per year of NOx.
 Require 1.5 to 1 offsets.
Requirements for Carbon Monoxide Nonattainment Areas
As with ozone nonattainment areas, carbon monoxide (CO) nonattainment areas are subjected to
specified control requirements, with more stringent requirements in Serious nonattainment areas.
A summary of the primary CO control requirements for each nonattainment category follows.
Moderate Areas
 Conduct an inventory of emissions sources.
 Forecast total vehicle miles traveled in the area.
 Adopt an enhanced vehicle inspection and maintenance program.
 Demonstrate annual improvements sufficient to attain the standard.
Serious Areas
 Adopt specified transportation control measures.
 Implement an oxygenated fuels program for all vehicles in the area.
 Reduce definition of a major source of CO from emissions of 100 tons per year
to 50 tons per year if stationary sources contribute significantly to the CO
problem.
Serious areas failing to attain the standard by the deadline had to revise their SIP and demonstrate
reductions of 5% per year until the standard was attained. As stated earlier, all areas have now
attained the standard.
Requirements for Particulate Nonattainment Areas
Particulate (PM10) nonattainment areas are also subject to specified control requirements. These
are the following:
Moderate Areas
 Require permits for new and modified major stationary sources of PM10.
 Impose reasonably available control measures (RACM).
Serious Areas
 Impose best available control measures (BACM).
 Reduce definition of a major source of PM10 from 100 tons per year to 70 tons
per year.
In July 1997, EPA promulgated new standards for fine particulates (PM2.5). Implementation of the
PM2.5 standards was delayed by court challenges and by the initial absence of a monitoring
network capable of measuring the pollutant. Nonattainment areas for PM2.5 were designated on
April 14, 2005. States had three years subsequent to designation to submit State Implementation
Plans. Revisions to the NAAQS promulgated in October 2006 and January 2013 strengthened the
PM2.5 standard and triggered new rounds of nonattainment area designations.
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Transported Air Pollution
Meeting the nation’s clean air standards can be complicated, as air pollution is no respecter of
political boundaries or subdivisions. This problem of transported air pollutants has come into
particular focus as states and EPA attempt to develop effective compliance strategies to achieve
both the ozone and the PM2.5 NAAQS. Under Section 110(a)(2)(D), SIPs must include adequate
provisions to prevent sources within that state from contributing significantly to nonattainment in
one or more downwind states. This provision is often referred to as the act’s “Good Neighbor”
provision.
The Clean Air Act provides statutory authorities to facilitate compliance with the Good Neighbor
provision. For example, if EPA finds a SIP inadequate to achieve a NAAQS, it must require the
affected state to submit a revised SIP that includes sufficient measures to bring that state into
compliance. This is known as a “SIP Call.” The 1990 Clean Air Act amendments provided EPA
and the states with new tools to address the transport problem. One of those tools is Section
176A, a provision that permits EPA, either on its own or by petition from any state, to establish a
transport region to address regional pollution problems contributing to violations of a primary
NAAQS. A commission of EPA and state officials is constituted to make recommendations to
EPA on appropriate mitigation strategies. Based on the commission’s findings and
recommendations, EPA is then required under section 110(k)(5) to notify affected states of
inadequacies in their current state implementation plans and to establish deadlines (not to exceed
18 months) for submitting necessary revisions. Besides authorizing administratively-created
transport regions, the 1990 amendments statutorily created an Ozone Transport Region (OTR) in
the Northeast. This provision (Section 184 of the act) required specific additional controls for all
areas (not only nonattainment areas) in that region, and established the Ozone Transport
Commission for the purpose of recommending to EPA region-wide controls affecting all areas in
the region.
The transport issue may also be addressed by affected downwind states through a Section 126
petition. As amended by the 1990 Clean Air Act amendments, under Section 126(b) any state or
political subdivision may petition EPA for a finding that a major source or group of stationary
sources located in another state is emitting pollutants that “significantly contribute” to the
nonattainment of a NAAQS by their state. EPA is to respond to the petition within 60 days. If the
petition is granted, the offending sources must cease operations within three months unless the
sources comply with emission controls and the compliance schedules as determined by EPA to
bring them into compliance with the section. For more information about interstate transport
issues under the Clean Air Act, see CRS Report R45299, The Clean Air Act’s Good Neighbor
Provision: Overview of Interstate Air Pollution Control, by Kate C. Shouse.
Emission Standards for Mobile Sources
Title II of the Clean Air Act has required emission standards for automobiles since 1968. The
1990 amendments significantly tightened these standards: for light-duty vehicles (a category that
includes cars, SUVs, minivans, and most pickup trucks), the hydrocarbon standard was reduced
by 40% and the nitrogen oxides (NOx) standard by 50%. These standards—referred to as “Tier 1”
standards—were phased in over the 1994-1996 model years.
The amendments envisioned a further set of reductions (“Tier 2” standards), but not before model
year 2004. For Tier 2 standards to be promulgated, the agency was first required to report to
Congress concerning the need for further emission reductions, the availability of technology to
achieve such reductions, and the cost-effectiveness of such controls compared to other means of
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attaining air quality standards. EPA submitted this report to Congress in August 1998, concluding
that further emission reductions were needed and that technology to achieve such reductions was
available and cost-effective. Tier 2 standards, requiring emission reductions of 77% to 95% from
cars and light trucks were promulgated in February 2000, and were phased in over the 2004-2009
model years. To facilitate the use of more effective emission controls, the standards also required
a more than 90% reduction in the sulfur content of gasoline, beginning in 2004. In 2014, EPA
completed a similar process to impose “Tier 3” standards on light duty vehicles and gasoline. The
Tier 3 standards, which are being phased in between 2017 and 2025, will require further
reductions of 70-80% in emissions, as compared to Tier 2, and have already cut the remaining
sulfur in gasoline by two-thirds.
The 1990 amendments also required that oxygenated gasoline, designed to reduce emissions of
carbon monoxide, be sold in the worst CO nonattainment areas and that “reformulated” gasoline
(RFG), designed to reduce emissions of volatile organic compounds and toxic air pollutants, be
sold in the nine worst ozone nonattainment areas (Los Angeles, San Diego, Houston, Baltimore,
Philadelphia, New York, Hartford, Chicago, and Milwaukee); metropolitan Washington, DC, and
four areas in California were added to the mandatory list later. Other ozone nonattainment areas
can opt in to the RFG program; additional areas in 14 states have done so, although several
subsequently opted out.
The fuels provisions were modified by the Energy Policy Act of 2005 (EPACT), removing the
requirement that RFG contain oxygenates. Instead, EPACT required the use of increasing
amounts of renewable fuel, most likely to be ethanol, in motor fuels, beginning in 2006. The
Energy Independence and Security Act of 2007 further strengthened the renewable fuel
requirements.
Use of alternative fuels and development of cleaner engines was also to be stimulated by the
Clean Fuel Fleet Program. In all of the most seriously polluted ozone and CO nonattainment
areas, centrally fueled fleets of 10 or more passenger cars and light-duty trucks had to purchase at
least 30% clean-fuel vehicles when they add new vehicles to existing fleets, starting in 1999. (The
act originally required the program to begin in 1998, but the start was delayed by a year.) The
percentage rose to 50% in 2000 and 70% in 2001. Heavy-duty fleets were required to purchase at
least 50% clean-fuel vehicles annually. A clean-fuel vehicle is one which meets Low Emission
Vehicle (LEV) standards and operates on reformulated gasoline, reformulated diesel, methanol,
ethanol, natural gas, liquefied petroleum gas, hydrogen, or electricity.
The 1990 amendments also imposed tighter requirements on emissions allowed during refueling,
on low temperature CO emissions, on in-use performance over time, on warranties for the most
expensive emission control components (8 years/80,000 miles for the catalytic converter,
electronic emissions control unit, and onboard emissions diagnostic unit), and on certification (an
auto’s useful life was defined as 100,000 miles instead of the earlier 50,000 miles—a figure since
increased through regulation to 120,000 or 150,000 miles depending on the standards).
Regulations were also extended to include nonroad fuels and engines.
Standards for trucks and buses using diesel engines were also strengthened. The 1990
amendments required new urban buses to reduce emissions of diesel particulates 92% by 1996,
and all other heavy-duty diesel engines to achieve an 83% reduction by the same year. NOx
emissions must also be reduced, 33% by 1998. Authority to further strengthen these standards led
to promulgation in January 2001 of new emission standards requiring a further 90%-95%
reduction in emissions phased in over the 2007-2010 model years, and a reduction of 97% in the
allowable amount of sulfur in highway diesel fuel. These regulations were followed in May 2004
by similar requirements for nonroad diesel equipment, which were phased in between 2007 and
2015.
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In addition to the CAA’s specific requirements discussed above, Section 202 of the act requires
the EPA administrator to prescribe “standards applicable to the emission of any air pollutant
[emphasis added] from any class or classes of new motor vehicles or new motor vehicle engines,
which in his judgment cause, or contribute to, air pollution which may reasonably be anticipated
to endanger public health or welfare.” Beginning in 2010, this language has been used to
authorize standards for greenhouse gas (GHG) emissions from cars and trucks. EPA has
promulgated three rounds of GHG standards for light duty vehicles, covering model years 2012-
2026, and two rounds of GHG standards for medium- and heavy-duty trucks, covering model
years 2014-2027. EPA has subsequently reviewed some of these standards, twice changing the
GHG standards for new light-duty vehicles for model years 2021 to 2026.5 For additional
information, see CRS In Focus IF10871, Vehicle Fuel Economy and Greenhouse Gas Standards,
by Richard K. Lattanzio and Bill Canis.
Questions of federal preemption of state regulations can arise when state law operates in an area
that may also be of concern to the federal government. Under the Supremacy Clause of the U.S.
Constitution,6 state law that conflicts with federal law must yield to the exercise of Congress’s
powers.7 When it acts, Congress can preempt state laws or regulations within a field entirely,
preempt only state laws or regulations that conflict with federal law, or allow states to act freely.8
Title II of the CAA generally preempts states from adopting their own emission standards for new
motor vehicles or engines.9 However, CAA Section 209(b) provides an exception to federal
preemption of state vehicle emission standards:
The [EPA] Administrator shall, after notice and opportunity for public hearing, waive
application of this section [the preemption of State emission standards] to any State which
has adopted standards (other than crankcase emission standards) for the control of
emissions from new motor vehicles or new motor vehicle engines prior to March 30, 1966,
if the State determines that the State standards will be, in the aggregate, at least as protective
of public health and welfare as applicable Federal standards. (footnote: CAA §209(a), 42
U.S.C. §7543(a). See also S.Rept. 91-1196, at 32 (1970). The CAA places three conditions
on the grant of such waivers: The Administrator is to deny a waiver if he finds: (1) that the
state’s determination is arbitrary and capricious; (2) that the state does not need separate
standards to meet compelling and extraordinary conditions; or (3) that the state’s standards
and accompanying enforcement procedures are not consistent with Section 202(a) of the
act. (42 U.S.C. §7543(b)(1)(A)-(C).)
Only California can qualify for such a preemption waiver because it is the only state that adopted
motor vehicle emission standards “prior to March 30, 1966.” According to EPA records, since
1967, California has submitted over 100 waiver requests for new or amended standards or “within
the scope” determinations (i.e., a request that EPA rule on whether a new state regulation is within
the scope of a waiver that EPA has already issued).10 Additionally, the CAA allows other states to

5 EPA and National Highway Traffic Safety Administration, “The Safer Affordable Fuel-Efficient (SAFE) Vehicles
Rule for Model Years 2021-2026 Passenger Cars and Light Trucks,” 85 Federal Register 24174, April 30, 2020; and
EPA, “Revised 2023 and Later Model Year Light-Duty Vehicle Greenhouse Gas Emissions Standards,” 86 Federal
Register 74434, December 30, 2021.
6 U.S. Const. art. VI, cl. 2.
7 Gade v. Nat'l Solid Wastes Mgmt. Assn., 505 U.S. 88, 108 (1992).
8 Ibid., p. 98. Congress can disavow an intent to preempt certain categories of state law by including a “savings clause”
to that effect in federal statutes, see, e.g., 29 U.S.C. §1144(b), or by allowing federal administrative agencies to grant
“preemption waivers” to states in certain circumstances, see 42 U.S.C. §7543(b).
9 CAA §209(a), 42 U.S.C. §7543(a). See also S.Rept. 91-1196, at 32 (1970).
10 See EPA, Vehicle Emissions California Waivers and Authorizations, https://www.epa.gov/state-and-local-
transportation/vehicle-emissions-california-waivers-and-authorizations#state (listing Federal Register notices of waiver
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adopt California’s motor vehicle emission standards under certain conditions.11 Section 177
requires, among other things, that such standards be identical to the California standards for
which a waiver has been granted. States are not required to seek EPA approval under the terms of
Section 177.
Hazardous Air Pollutants
Completely rewritten by the Clean Air Act Amendments of 1990, Section 112 of the act
establishes programs for protecting public health and the environment from exposure to toxic air
pollutants. As revised by the 1990 amendments, the section contains four major provisions:
Maximum Achievable Control Technology (MACT) requirements; health-based standards;
Generally Available Control Technology (GACT) standards for stationary “area sources” (small,
but numerous sources, such as gas stations or dry cleaners, that collectively emit significant
quantities of hazardous pollutants); and requirements for the prevention of catastrophic releases.
First, EPA is to establish technology-based emission standards, called MACT standards, for
sources of 187 pollutants listed in the legislation, and to specify categories of sources subject to
the emission standards.12 EPA is to revise the standards periodically (at least every eight years).
EPA can, on its own initiative or in response to a petition, add or delete substances or source
categories from the lists.
Section 112 establishes a presumption in favor of regulation for the designated chemicals; it
requires regulation of a designated pollutant unless EPA or a petitioner is able to show “that there
is adequate data on the health and environmental effects of the substance to determine that
emissions, ambient concentrations, bioaccumulation or deposition of the substance may not
reasonably be anticipated to cause any adverse effects to human health or adverse environmental
effects” (Clean Air Act Section 112(b)(3)).
EPA is required to set standards for sources of the listed pollutants that achieve “the maximum
degree of reduction in emissions” taking into account cost and other non-air-quality factors.
These MACT standards for new sources “shall not be less stringent than the most stringent
emissions level that is achieved in practice by the best controlled similar source” (Clean Air Act
Section 112(d)(3)). The standards for existing sources may be less stringent than those for new
sources, but must be no less stringent than the emission limitations achieved by either the best
performing 12% of existing sources (if there are more than 30 such sources in the category or
subcategory) or the best performing 5 similar sources (if there are fewer than 30). Existing
sources are given three years following promulgation of standards to achieve compliance, with a
possible one-year extension; additional extensions may be available for special circumstances or
for certain categories of sources. Existing sources that achieve voluntary early emissions
reductions received a six-year extension for compliance with MACT.
The second major provision of Section 112 directs EPA to set health-based standards to address
situations in which a significant residual risk of adverse health effects or a threat of adverse
environmental effects remains after installation of MACT. This provision requires that EPA, after
consultation with the Surgeon General of the United States, submit a report to Congress on the

requests and decisions); Letter from Kevin de Leon, president pro tempore, Cal. Senate, et al., to Xavier Becerra, Att’y
Gen., Cal. Dep’t of Justice, March 16, 2017.
11 42 U.S.C. §7507.
12 The 1990 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 removed methyl ethyl ketone
(MEK) from the list of toxic air pollutants. The total number of listed air toxics is now 187.
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public health significance of residual risks, and recommend legislation regarding such risks. If
Congress does not legislate in response to EPA’s recommendations, then EPA is required to issue
standards for categories of sources of hazardous air pollutants as necessary to protect the public
health with an ample margin of safety or to prevent an adverse environmental effect. A residual
risk standard is required for any source emitting a cancer-causing pollutant that poses an added
risk to the most exposed person of more than one-in-a-million. Residual risk standards are due
eight years after promulgation of MACT for the affected source category. Existing sources have
90 days to comply with a residual risk standard, with a possible 2-year extension. In general,
residual risk standards do not apply to area sources.
The law directed EPA to contract with the National Academy of Sciences (NAS) for a study of
risk assessment methodology, and created a Risk Assessment and Management Commission to
investigate and report on policy implications and appropriate uses of risk assessment and risk
management. In 1994 NAS published its report, Science and Judgment in Risk Assessment. The
Commission study, Framework for Environmental Health Risk Management, was released in
1997.
Third, in addition to the technology-based and health-based programs for major sources of
hazardous air pollution, EPA is to establish standards for stationary “area sources” determined to
present a threat of adverse effects to human health or the environment. The provision requires
EPA to regulate the stationary area sources responsible for 90% of the emissions of the 30
hazardous air pollutants that present the greatest risk to public health in the largest number of
urban areas. In setting the standard, EPA can impose less stringent “generally available” control
technologies, rather than MACT.
Finally, Section 112 addresses prevention of sudden, catastrophic releases of air toxics by
establishing an independent Chemical Safety and Hazard Investigation Board. The Board is
responsible for investigating accidents involving releases of hazardous substances, conducting
studies, and preparing reports on the handling of toxic materials and measures to reduce the risk
of accidents.
EPA is also directed to issue prevention, detection, and correction requirements for catastrophic
releases of air toxics by major sources. Section 112(r) requires owners and operators to prepare
risk management plans including hazard assessments, measures to prevent releases, and a
response program. See CRS Report R44952, EPA’s Role in Emergency Planning and Notification
at Chemical Facilities, by Richard K. Lattanzio and David M. Bearden.
New Source Performance Standards
Section 111 of the act requires EPA to establish nationally uniform, technology-based standards
(called New Source Performance Standards, or NSPS) for categories of new industrial facilities.
These standards accomplish two goals: first, they establish a consistent baseline for pollution
control that competing firms must meet, and thereby remove any incentive for states or
communities to weaken air pollution standards in order to attract polluting industry; and second,
they preserve clean air to accommodate future growth, as well as for its own benefits.
NSPS establish maximum emission levels for new major stationary sources—power plants, steel
mills, and smelters, for example—with the emission levels determined by the best system of
emission reduction (BSER) “adequately demonstrated,” taking costs into account. At least every
eight years, EPA must review and, if appropriate, revise NSPS applicable to designated sources,
since the goal is to prevent new pollution problems from developing and to force the installation
of new control technology.
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The standards also apply to modifications of existing facilities, through a process called New
Source Review (NSR). The law’s ambiguity regarding what constitutes a modification (subject to
NSR) as opposed to routine maintenance of a facility has led to litigation, with EPA proposing in
recent years to modify its interpretation of the requirements of this section.
Section 111 can also be used to set standards for existing stationary sources of pollution. Under
Section 111(d), EPA is to require the states to submit plans establishing standards of performance
for existing sources that would be subject to NSPS if they were new, unless the sources or the
pollutants regulated by the NSPS are already subject to standards under other sections of the act.
This authority has rarely been used, because most pollutants and sources are subject to regulation
under other sections of the act; but it served as the basis of a rulemaking intended to limit carbon
dioxide emissions from existing fossil-fueled power plants,13 methane emissions from existing
crude oil and natural gas production, transmission, and storage equipment,14 and methane
emissions from existing municipal solid waste landfills.15
Solid Waste Incinerators
Prior to 1990, solid waste incinerators, which emit a wide range of pollutants, were subject to
varying degrees of state and federal regulation depending on their size, age, and the type of waste
burned. In a new Section 129, the 1990 amendments established more consistent federal
requirements specifying that emissions of 10 categories of pollutants be regulated at new and
existing incinerators burning municipal solid waste, medical waste, and commercial and
industrial waste. The amendments also established emissions monitoring and operator training
requirements.
Prevention of Significant Deterioration / Regional
Haze
Sections 160-169 of the act establish requirements for the prevention of significant deterioration
of air quality (PSD). The PSD program reflects the principle that areas where air quality is better
than that required by NAAQS should be protected from significant new air pollution even if
NAAQS would not be violated.
The act divides clean air areas into three classes, and specifies the increments of sulfur dioxide
(SO2) and particulate pollution allowed in each. Class I areas include international and national
parks, wilderness and other pristine areas; allowable increments of new pollution are very small.
Class II areas include all attainment and not classifiable areas, not designated as Class I;

13 In 2015, EPA promulgated the Clean Power Plan under Section 111(d) authority to limit carbon dioxide emissions
from existing fossil-fueled power plants. In 2019, EPA repealed the Clean Power Plan and promulgated new emission
guidelines in the Affordable Clean Energy Rule. See EPA, “Repeal of the Clean Power Plan; Emission Guidelines for
Greenhouse Gas Emissions from Existing Electric Utility Generating Units; Revisions to Emission Guidelines
Implementing Regulations,” 84 Federal Register 32521, July 8, 2019. Various states and stakeholders challenged the
Affordable Clean Energy Rule and Clean Power Plan repeal. On January 19, 2021, a three-judge panel of the D.C.
Circuit vacated the ACE Rule and the CPP repeal in a split decision, though it later granted EPA’s request not to
reinstate the CPP until EPA considers a new rulemaking action.
14 EPA, “Standards of Performance for New, Reconstructed, and Modified Sources and Emissions Guidelines for
Existing Sources: Oil and Natural Gas Sector Climate Review, Proposed Rule,” 83 Federal Register 63110, November
15, 2021.
15 EPA, “Emission Guidelines and Compliance Times for Municipal Solid Waste Landfills,” 81 Federal Register
59276, August 29, 2016.
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allowable increments of new pollution are modest. Class III represents selected areas that states
may designate for development; allowable increments of new pollution are large (but not so large
that the area would exceed NAAQS). Through an elaborate hearing and review process, a state
can have regions redesignated from Class II to Class III (although no Class III areas have yet
been designated).
While the 1977 amendments only stipulated PSD standards for two pollutants, SO2 and
particulates, EPA is supposed to establish standards for other criteria pollutants. Thus far, only
one of the other four (NO2) has been addressed: the agency promulgated standards for NO2 in
1988.
Newly constructed polluting sources in PSD areas must install best available control technology
(BACT) that may be more strict than that required by NSPS. The justifications of the policy are
that it protects air quality, provides an added margin of health protection, preserves clean air for
future development, and prevents firms from gaining a competitive edge by “shopping” for clean
air to pollute.
In Sections 169A and B, the act also sets a national goal of preventing and remedying impairment
of visibility in national parks and wilderness areas, and requires EPA to promulgate regulations to
assure reasonable progress toward that goal. In the 1990 Amendments, Congress strengthened
these provisions, which had not been implemented.
The amendments required EPA to establish a Grand Canyon Visibility Transport Commission,
composed of Governors from each state in the affected region, an EPA designee, and a
representative of each of the national parks or wilderness areas in the region. Other visibility
transport commissions can be established upon EPA’s discretion or upon petition from at least
two states. Within 18 months of receiving a report from one of these commissions, EPA is
required to promulgate regulations to assure reasonable progress toward the visibility goal,
including requirements that states update their State Implementation Plans to contain emission
limits, schedules of compliance, and other measures necessary to make reasonable progress.
Specifically mentioned is a requirement that states impose Best Available Retrofit Technology on
existing sources of emissions impairing visibility.
The Grand Canyon Commission delivered a set of recommendations to EPA in June 1996, and the
agency subsequently promulgated a “regional haze” program applicable to all 50 states under this
authority.
Acid Deposition Control
The Clean Air Act Amendments of 1990 added an acid deposition control program (Title IV) to
the act. It set goals for the year 2000 of reducing annual SO2 emissions by 10 million tons from
1980 levels and reducing annual NOx emissions by 2 million tons, also from 1980 levels.
The SO2 reductions were imposed in two steps. Under Phase 1, owners/operators of 110 high-
emitting electric generating facilities listed in the law had to meet tonnage emission limitations by
January 1, 1995. This would reduce SO2 emissions by about 3.5 million tons. Phase 2 included
facilities with a nameplate capacity greater than or equal to 75 megawatts, with a deadline of
January 1, 2000. Compliance was 100%.
To introduce some flexibility in the distribution and timing of reductions, the act creates a
comprehensive permit and emissions allowance system. An allowance is a limited authorization
to emit a ton of SO2. Issued by EPA, the allowances would be allocated to Phase 1 and Phase 2
units in accordance with baseline emissions estimates. Power plants which commence operation
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after November 15, 1990 would not receive any allowances. These new units would have to
obtain allowances (offsets) from holders of existing allowances. Allowances were allowed to be
traded nationally during either phase. The law also permitted industrial sources and power plants
to sell allowances to utility systems under regulations developed by EPA. Allowances were
allowed to be banked by a utility for future use or sale.
The act provided for two types of sales to improve the liquidity of the allowance system and to
ensure the availability of allowances for utilities and independent power producers who need
them. First, a special reserve fund consisting of 2.8% of Phase 1 and Phase 2 allowance
allocations was set aside for sale. Allowances from this fund (25,000 annually from 1993 to 1999
and 50,000 thereafter) were sold at a fixed price of $1,500 an allowance. Independent power
producers had guaranteed rights to these allowances under certain conditions. Second, an annual,
open auction sold allowances (150,000 from 1993 to 1995, and 250,000 from 1996 to 1999) with
no minimum price. Utilities with excess allowances could have them auctioned off at this auction,
and any person could buy allowances.
The act essentially capped SO2 emissions at individual existing sources through a tonnage
limitation, and at future plants through the allowance system. First, emissions from most existing
sources were capped at a specified emission rate times an historic baseline level. Second, for
plants commencing operation after November 15, 1990, emissions had to be completely offset
with additional reductions at existing facilities beginning after Phase 2 compliance. However, as
noted above, the law provided some allowances to future power plants which met certain criteria.
The utility SO2 emission cap was set at 8.9 million tons, with some exceptions.
The act provided that if an affected unit did not have sufficient allowances to cover its emissions,
it would be subject to an excess emission penalty of $2,000 per ton of SO2 and required to reduce
an additional ton of SO2 the next year for each ton of excess pollutant emitted.
The act also required EPA to inventory industrial emissions of SO2 and to report every five years,
beginning in 1995. If the inventory showed that industrial emissions may reach levels above 5.60
million tons per year, then EPA was to take action under the act to ensure that the 5.60 million ton
cap would not be exceeded.
The act required EPA to set specific NOx emission rate limitations—0.45 lb. per million Btu for
tangentially-fired boilers and 0.50 lb. per million Btu for wall-fired boilers—unless those rates
cannot be achieved by low-NOx burner technology. Tangentially and wall-fired boilers affected by
Phase 1 SO2 controls must also meet NOx requirements. EPA was to set emission limitations for
other types of boilers by 1997 based on low-NOx burner costs, which EPA did. In addition, EPA
was to propose and promulgate a revised new source performance standard for NOx from fossil
fuel steam generating units, which EPA also did, in 1998.
In 2005, 2011, and 2016, EPA used the authority described in the section on “Transported Air
Pollution” to further lower the caps on SO2 and NOx emissions in the eastern half of the country.
As a result, SO2 and NOx emissions have been reduced by at least a further 50% since 2005.
Permits
The Clean Air Act Amendments of 1990 added a Title V to the act which requires states to
administer a comprehensive permit program for the operation of sources emitting air pollutants.
These requirements are modeled after similar provisions in the Clean Water Act. Previously, the
Clean Air Act contained limited provision for permits, requiring only new or modified major
stationary sources to obtain construction permits (under Section 165 of the act).
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Sources subject to the permit requirements generally include major sources that emit or have the
potential to emit 100 tons per year of any regulated pollutant, plus stationary and area sources that
emit or have potential to emit lesser specified amounts of hazardous air pollutants. However, in
nonattainment areas, the permit requirements also include sources which 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).
States were required to develop permit programs and to submit those programs for EPA approval
by November 15, 1993. EPA had one year to approve or disapprove a state’s submission in whole
or in part. After the effective date of a state plan, sources had 12 months to submit an actual
permit application.
States are to collect annual fees from sources sufficient to cover the “reasonable costs” of
administering the permit program, with revenues to be used to support the agency’s air pollution
control program. The fee must be at least $25 per ton of regulated pollutants (excluding carbon
monoxide). Permitting authorities have discretion not to collect fees on emissions in excess of
4,000 tons per year and may collect other fee amounts, if appropriate.
The permit states how much of which air pollutants a source is allowed to emit. As a part of the
permit process, a source must prepare a compliance plan and certify compliance. The term of
permits is limited to no more than five years; sources are required to renew permits at that time.
State permit authorities must notify contiguous states of permit applications that may affect them;
the application and any comments of contiguous states must be forwarded to EPA for review. EPA
can veto a permit; however, this authority is essentially limited to major permit changes. EPA
review need not include permits which simply codify elements of a state’s overall clean air plan,
and EPA has discretion to not review permits for small sources. Holding a permit to some extent
shields a source from enforcement actions: the act provides that a source cannot be held in
violation if it is complying with explicit requirements addressed in a permit, or if the state finds
that certain provisions do not apply to that source.
Enforcement
Section 113 of the act, which was also strengthened by the 1990 amendments, covers
enforcement. The section establishes federal authority to issue agency and court orders requiring
compliance and to impose penalties for violations of Act requirements. Section 114 authorizes
EPA to require sources to submit reports, monitor emissions, and certify compliance with the
act’s requirements, and authorizes EPA personnel to conduct inspections.
Like most federal environmental statutes, the Clean Air Act is enforced primarily by states or
local governments; they issue most permits, monitor compliance, and conduct the majority of
inspections. The federal government functions as a backstop, with authority to review state
actions. The agency may act independently or may file its own enforcement action in cases where
it concludes that a state’s response was inadequate.
The act also provides for citizen suits both against persons (including corporations or government
agencies) alleged to have violated emissions standards or permit requirements, and against EPA in
cases where the administrator has failed to perform an action that is not discretionary under the
act. Citizen groups have often used the latter provision to compel the administrator to promulgate
regulations required by the statute.
The 1990 Amendments elevated penalties for some knowing violations from misdemeanors to
felonies; removed the ability of a source to avoid an enforcement order or civil penalty by ceasing
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a violation within 60 days of notice; gave authority to EPA to assess administrative penalties; and
authorized $10,000 awards to persons supplying information leading to convictions under the act.
Stratospheric Ozone Protection
Title VI of the 1990 Clean Air Act Amendments represents the United States’ primary response
on the domestic front to the stratospheric ozone depletion issue. It also implements the U.S.
international responsibilities under the Montreal Protocol on Substances that Deplete the Ozone
Layer (and its amendments). Indeed, Section 606(a)(3) provides that EPA shall adjust phase-out
schedules for ozone-depleting substances in accordance with any future changes in Montreal
Protocol schedules. As a result, the phase-out schedules contained in Title VI for various ozone-
depleting compounds have now been superseded by subsequent amendments to the Montreal
Protocol.
Since passage of Title VI, depleting substances such as CFCs, methyl chloroform, carbon
tetrachloride, and halons (referred to as Class 1 substances) have been phased out by industrial
countries, including the United States. New uses of hydrochlorofluorocarbons (HCFCs) (called
Class 2 substances under Title VI) were banned beginning January 1, 2015, unless the HCFCs are
recycled, used as a feedstock, or used as a refrigerant for appliances manufactured prior to
January 1, 2020. Production of HCFCs is to be frozen January 1, 2015, and phased out by January
1, 2030. Exemptions consistent with the Montreal Protocol are allowed.
EPA is required to add any substance with an ozone depletion potential (ODP) of 0.2 or greater to
the list of Class 1 substances and set a phase-out schedule of no more than seven years. For
example, methyl bromide (ODP estimated by EPA at 0.7) was added to the list in December 1993,
requiring its phaseout by January 1, 2001; this decision was altered by Congress in 1998 to
harmonize the U.S. methyl bromide phase-out schedule with the 2005 deadline set by the parties
to the Montreal Protocol in 1997. Also, EPA is required to add any substance that is known or
may be reasonably anticipated to harm the stratosphere to the list of Class 2 substances and set a
phase-out schedule of no more than ten years.
Title VI contains several implementing strategies to avoid releases of ozone-depleting chemicals
to the atmosphere, including (1) for Class 1 substances used as refrigerants—lowest achievable
level of use and emissions, maximum recycling, and safe disposal required by July 1, 1992; (2)
for servicing or disposing refrigeration equipment containing Class 1 and 2 substances—venting
banned as of July 1, 1992; (3) for motor vehicle air conditioners containing Class 1 or 2
substances—recycling required by January 1, 1992 (smaller shops by January 1, 1993); (4) sale of
small containers of class 1 and 2 substances—banned within two years of enactment; and (5)
nonessential products—banned within two years of enactment.
Selected References
U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards, Air Trends.
Compiled annually, and available at http://www.epa.gov/airtrends/.
Julie R. Domike and Alec Chatham Zacaroli (eds.), The Clean Air Act Handbook, 4th edition
(Chicago: American Bar Association) 2016, 864 p.
CRS Report R43699, Key Historical Court Decisions Shaping EPA’s Program Under the Clean
Air Act, by Linda Tsang.
CRS Report R46684, Clean Air Act Issues in the 117th Congress, by Kate C. Shouse.
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Table 4. Major U.S. Code Sections of the Clean Air Act
(codified generally as 42 U.S.C. 7401-7671)
Clean Air Act, as
42 U.S.C.
Section Title
amended
Subchapter I -
Programs and Activities

Part A -
Air Quality and Emissions Limitations

7401
Congressional findings and declaration of purpose
Sec. 101
7402
Cooperative activities
Sec. 102
7403
Research, investigation, training, and other activities
Sec. 103
7404
Research relating to fuels and vehicles
Sec. 104
7405
Grants for support of air pol ution planning and control programs
Sec. 105
7406
Interstate air quality agencies; program cost limitations
Sec. 106
7407
Air quality control regions
Sec. 107
7408
Air quality criteria and control techniques
Sec. 108
7409
National primary and secondary ambient air quality standards
Sec. 109
7410
State Implementation Plans for national primary and secondary
Sec. 110
ambient air quality standards
7411
Standards of performance for new stationary sources
Sec. 111
7412
Hazardous air pol utants
Sec. 112
7413
Federal enforcement
Sec. 113
7414
Recordkeeping, inspections, monitoring, and entry
Sec. 114
7415
International air pol ution
Sec. 115
7416
Retention of state authority
Sec. 116
7417
Advisory committees
Sec. 117
7418
Control of pol ution from federal facilities
Sec. 118
7419
Primary nonferrous smelter orders
Sec. 119
7420
Noncompliance penalty
Sec. 120
7421
Consultation
Sec. 121
7422
Listing of certain unregulated pol utants
Sec. 122
7423
Stack heights
Sec. 123
7424
Assurance of adequacy of state plans
Sec. 124
7425
Measures to prevent economic disruption or unemployment
Sec. 125
7426
Interstate pol ution abatement
Sec. 126
7427
Public notification
Sec. 127
7428
State boards
Sec. 128
7429
Solid waste combustion
Sec. 129
7430
Emission factors
Sec. 130
7431
Land use authority
Sec. 131
7432
Clean heavy-duty vehicles
Sec. 132
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Clean Air Act, as
42 U.S.C.
Section Title
amended
7433
Grants to reduce air pol ution at ports
Sec. 133
7434
Greenhouse gas reduction fund
Sec. 134
7435
Low emissions electricity program
Sec. 135
7436
Methane emissions and waste reduction incentive program for
Sec. 136
petroleum and natural gas systems
7437
Greenhouse gas air pol ution plans and implementation grants
Sec. 137
7438
Environmental and climate justice block grants
Sec. 138

Part B - Ozone Protection (repealed—new provisions related to stratospheric ozone protection are found at 42
U.S.C. 7671 et seq., below)

Part C -
Prevention of Significant Deterioration of Air Quality
Subpart I -
Clean Air

7470
Congressional declaration of purpose
Sec. 160
7471
Plan requirements
Sec. 161
7472
Initial classifications
Sec. 162
7473
Increments and ceilings
Sec. 163
7474
Area redesignation
Sec. 164
7475
Preconstruction requirements
Sec. 165
7476
Other pol utants
Sec. 166
7477
Enforcement
Sec. 167
7478
Period before plan approval
Sec. 168
7479
Definitions
Sec. 169

Subpart II -
Visibility Protection

7491
Visibility protection for federal class I areas
Sec. 169A
7492
Visibility
Sec. 169B

Part D -
Plan Requirements for Nonattainment Areas

Subpart 1 -
Nonattainment Areas in General

7501
Definitions
Sec. 171
7502
Nonattainment plan provisions in general
Sec. 172
7503
Permit requirements
Sec. 173
7504
Planning procedures
Sec. 174
7505
Environmental Protection Agency grants
Sec. 175
7505a
Maintenance plans
Sec. 175A
7506
Limitations on certain federal assistance
Sec. 176
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Clean Air Act, as
42 U.S.C.
Section Title
amended
7506a
Interstate transport commissions
Sec. 176A
7507
New motor vehicle emission standards in nonattainment areas
Sec. 177
7508
Guidance documents
Sec. 178
7509
Sanctions and consequences of failure to attain
Sec. 179
7509a
International border areas
Sec. 179B

Subpart 2 -
Additional Provisions for Ozone Nonattainment Areas
7511
Classifications and attainment dates
Sec. 181
7511a
Plan submissions and requirements
Sec. 182
7511b
Federal ozone measures
Sec. 183
7511c
Control of interstate ozone air pol ution
Sec. 184
7511d
Enforcement for Severe and Extreme Ozone Nonattainment Areas
Sec. 185
for failure to attain
7511e
Transitional areas
Sec. 185A
7511f
NOx and VOC study
Sec. 185B

Subpart 3 -
Additional Provisions for Carbon Monoxide Nonattainment Areas
7512
Classification and attainment dates
Sec. 186
7512a
Plan submissions and requirements
Sec. 187

Subpart 4 -
Additional Provisions for Particulate Matter Nonattainment Areas
7513
Classifications and attainment dates
Sec. 188
7513a
Plan provisions and schedules for plan submissions
Sec. 189
7513b
Issuance of RACM and BACM guidance
Sec. 190

Subpart 5 -
Additional Provisions for Areas Designated Nonattainment for Sulfur Oxides, Nitrogen
Dioxide, or Lead
7514
Plan submission deadlines
Sec. 191
7514a
Attainment dates
Sec. 192

Subpart 6 -
Savings Provisions

7515
General savings clause
Sec. 193

Subchapter II -
Emission Standards for Moving Sources

Part A -
Motor Vehicle Emission and Fuel Standards

7521
Emission standards for new motor vehicles or new motor vehicle
Sec. 202
engines
7522
Prohibited acts
Sec. 203
Congressional Research Service

20

Clean Air Act: A Summary of the Act and Its Major Requirements

Clean Air Act, as
42 U.S.C.
Section Title
amended
7523
Actions to restrain violations
Sec. 204
7524
Civil penalties
Sec. 205
7525
Motor vehicle and motor vehicle engine compliance testing and
Sec. 206
certification
7541
Compliance by vehicles and engines in actual use
Sec. 207
7542
Information col ection
Sec. 208
7543
State standards
Sec. 209
7544
State grants
Sec. 210
7545
Regulation of fuels
Sec. 211
7547
Nonroad engines and vehicles
Sec. 213
7548
Study of particulate emissions from motor vehicles
Sec. 214
7549
High altitude performance adjustments
Sec. 215
7550
Definitions
Sec. 216
7552
Motor vehicle compliance program fees
Sec. 217
7553
Prohibition on production of engines requiring leaded gasoline
Sec. 218
7554
Urban bus standards
Sec. 219

Part B -
Aircraft Emission Standards

7571
Establishment of standards
Sec. 231
7572
Enforcement of standards
Sec. 232
7573
State standards and controls
Sec. 233
7574
Definitions
Sec. 234

Part C -
Clean Fuel Vehicles

7581
Definitions
Sec. 241
7582
Requirements applicable to clean-fuel vehicles
Sec. 242
7583
Standards for light-duty clean-fuel vehicles
Sec. 243
7584
Administration and enforcement as per California standards
Sec. 244
7585
Standards for heavy-duty clean-fuel vehicles
Sec. 245
7586
Centrally fueled fleets
Sec. 246
7587
Vehicle conversions
Sec. 247
7588
Federal agency fleets
Sec. 248
7589
California pilot test program
Sec. 249
7590
General provisions
Sec. 250

Subchapter III -
General Provisions

7601
Administration
Sec. 301
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21

Clean Air Act: A Summary of the Act and Its Major Requirements

Clean Air Act, as
42 U.S.C.
Section Title
amended
7602
Definitions
Sec. 302
7603
Emergency powers
Sec. 303
7604
Citizen suits
Sec. 304
7605
Representation in litigation
Sec. 305
7606
Federal procurement
Sec. 306
7607
Administrative proceedings and judicial review
Sec. 307
7608
Mandatory licensing
Sec. 308
7609
Policy review
Sec. 309
7610
Other authority
Sec. 310
7611
Records and audit
Sec. 311
7612
Economic impact analyses
Sec. 312
7614
Labor standards
Sec. 314
7615
Separability
Sec. 315
7616
Sewage treatment grants
Sec. 316
7617
Economic impact assessment
Sec. 317
7619
Air quality monitoring
Sec. 319
7620
Standardized air quality modeling
Sec. 320
7621
Employment effects
Sec. 321
7622
Employee protection
Sec. 322
7624
Cost of vapor recovery equipment
Sec. 323
7625
Vapor recovery for small business marketers of petroleum products
Sec. 324
7625-1
Exemptions for certain territories
Sec. 325
7625a
Statutory construction
Sec. 326
7626
Authorization of appropriations
Sec. 327
7627
Air pol ution from Outer Continental Shelf activities
Sec. 328

Subchapter IV-A Acid Deposition Control

7651
Findings and purposes
Sec. 401
7651a
Definitions
Sec. 402
7651b
Sulfur dioxide allowance program for existing and new units
Sec. 403
7651c
Phase I sulfur dioxide requirements
Sec. 404
7651d
Phase II sulfur dioxide requirements
Sec. 405
7651e
Allowances for states with emissions rates at or below 0.80
Sec. 406
lbs./mmBtu
7651f
Nitrogen oxides emission reduction program
Sec. 407
7651g
Permits and compliance plans
Sec. 408
7651h
Repowered sources
Sec. 409
Congressional Research Service

22

Clean Air Act: A Summary of the Act and Its Major Requirements

Clean Air Act, as
42 U.S.C.
Section Title
amended
7651i
Election for additional sources
Sec. 410
7651j
Excess emissions penalty
Sec. 411
7651k
Monitoring, reporting, and recordkeeping requirements
Sec. 412
7651l
General compliance with other provisions
Sec. 413
7651m
Enforcement
Sec. 414
7651n
Clean coal technology regulatory incentives
Sec. 415
7651o
Contingency guarantee, auctions, reserve
Sec. 416

Subchapter V -
Permits

7661
Definitions
Sec. 501
7661a
Permit programs
Sec. 502
7661b
Permit applications
Sec. 503
7661c
Permit requirements and conditions
Sec. 504
7661d
Notification to administrator and contiguous states
Sec. 505
7661e
Other authorities
Sec. 506
7661f
Small business stationary source technical and environmental
Sec. 507
compliance assistance program

Subchapter VI -
Stratospheric Ozone Protection

7671
Definitions
Sec. 601
7671a
Listing of class I and class II substances
Sec. 602
7671b
Monitoring and reporting requirements
Sec. 603
7671c
Phase-out of production and consumption of class I substances
Sec. 604
7671d
Phase-out of production and consumption of class II substances
Sec. 605
7671e
Accelerated schedule
Sec. 606
7671f
Exchange authority
Sec. 607
7671g
National recycling and emission reduction program
Sec. 608
7671h
Servicing of motor vehicle air conditioners
Sec. 609
7671i
Nonessential products containing chlorofluorocarbons
Sec. 610
7671j
Labeling
Sec. 611
7671k
Safe alternatives policy
Sec. 612
7671l
Federal procurement
Sec. 613
7671m
Relationship to other laws
Sec. 614
7671n
Authority of administrator
Sec. 615
7671o
Transfers among parties to Montreal Protocol
Sec. 616
7671p
International cooperation
Sec. 617
7671q
Miscellaneous provisions
Sec. 618
Congressional Research Service

23

Clean Air Act: A Summary of the Act and Its Major Requirements

[29 U.S.C. 655]
Chemical Process Safety Management
Sec. 304 of CAA of
1990
[29 U.S.C.
Clean Air Employment Transition Assistance
Sec. 1101 of CAA of
1662e]
1990
Note: This table shows only the major U.S. Code sections. For more detail and to determine when a section was
added, the reader should consult the official printed version of the U.S. Code.

Author Information

Richard K. Lattanzio

Specialist in Environmental Policy

Acknowledgments
Prior contributors to this report include James E. McCarthy, Larry B. Parker, Linda-Jo Schierow, Claudia
Copeland, and Kate C. Shouse.

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
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copy or otherwise use copyrighted material.

Congressional Research Service
RL30853 · VERSION 30 · UPDATED
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