Clean Air Act (United States)
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Clean Air Act United States

Clean Air Act
Great Seal of the United States
Long titleAn Act to improve, strengthen, and accelerate programs for the prevention and abatement of air pollution, as amended.
Acronyms (colloquial)CAA
U.S.C. sections created42 U.S.C. ch. 85 (§§ 7401-7671q)
Major amendments
Clean Air Act of 1963 (77 Stat. 392, Pub.L. 88-206)
Motor Vehicle Air Pollution Control Act of 1965 (79 Stat. 992, Pub.L. 89-272)
Air Quality Act of 1967 (81 Stat. 485, Pub.L. 90-148)
Clean Air Amendments of 1970 (84 Stat. 1676, Pub.L. 91-604)
Clean Air Act Amendments of 1977 (91 Stat. 685, Pub.L. 95-95)
Clean Air Act Amendments of 1990 (104 Stat. 2468, Pub.L. 101-549)
United States Supreme Court cases
Union Elec. Co. v. EPA, 427 U.S. 246 (1976)
Chevron v. NRDC, 467 U.S. 837 (1984)
Whitman v. Am. Trucking Ass'ns, 531 U.S. 457 (2001)
Massachusetts v. EPA, 549 U.S. 497 (2006)

The Clean Air Act is the United States' primary federal air quality law, intended to reduce and control air pollution nationwide. Initially enacted in 1963 and amended many times since, it is one of the United States' first and most influential modern environmental laws.

As with many other major U.S. federal environmental statutes, the Clean Air Act is administered by the U.S. Environmental Protection Agency (EPA), in coordination with state, local, and tribal governments.[1] EPA develops extensive administrative regulations to carry out the law's mandates. The associated regulatory programs are often technical and complex. Among the most important, the NAAQS program sets standards for concentrations of certain pollutants in outdoor air; the NESHAPS program sets standards for emissions of particular hazardous pollutants from specific sources. Other programs create requirements for vehicle fuels, industrial facilities, and other technologies and activities that impact air quality. Newer programs tackle specific problems, including acid rain, ozone layer protection, and climate change.

Although its exact benefits depend on what is counted, the Clean Air Act has substantially reduced air pollution and improved US air quality - benefits which EPA credits with saving trillions of dollars and many thousands of lives each year.

Regulatory Programs

In the United States, the "Clean Air Act" typically refers to the codified statute at 42 U.S.C. ch. 85. That statute is the product of multiple acts of Congress, one of which - the 1963 act - was actually titled the Clean Air Act, and another of which - the 1970 act - is most often referred to as such. In the U.S. Code, the statute itself is divided into subchapters, and the section numbers are not clearly related to the subchapters. However in the bills that created the law, the major divisions are called "Titles," and the law's sections are numbered according to the title (e.g., Title II begins with Section 201).[2] In practice, EPA, courts, and attorneys often use the latter numbering scheme.

Although many parts of the statute are quite detailed, others set out only the general outlines of the law's regulatory programs, and leave many key terms undefined. Responsible agencies - primarily EPA - have therefore developed administrative regulations to carry out Congress's instructions. EPA's proposed and final regulations are published in the Federal Register, often with lengthy background histories. The existing CAA regulations are codified at 40 C.F.R. Subchapter C, Parts 50-98.[3] These Parts more often correspond to the Clean Air Act's major regulatory programs.

Today, the following are major regulatory programs under the Clean Air Act.

National Ambient Air Quality Standards (NAAQS)

The NAAQS govern how much ground-level ozone (O3), carbon monoxide (CO), particulate matter (PM10, PM2.5), lead (Pb), sulfur dioxide (SO2), and nitrogen dioxide (NO2) are allowed in the outdoor air. [4] The NAAQS set the acceptable levels of certain air pollutants in the ambient air in the United States. Prior to 1965, there was no national program for developing ambient air quality standards, and prior to 1970 the federal government did not have primary responsibility for developing them. The 1970 CAA amendments required EPA to determine which air pollutants posed the greatest threat to public health and welfare and promulgate NAAQS and air quality criteria for them. The health-based standards were called "primary" NAAQS, while standards set to protect public welfare other than health (e.g., agricultural values) were called "secondary" NAAQS. In 1971, EPA promulgated regulations for sulfur oxides, particulate matter, carbon monoxide, photochemical oxidants, hydrocarbons, and nitrogen dioxide (36 FR 22384). Initially, EPA did not list lead as a criteria pollutant, controlling it through mobile source authorities, but it was required to do so after successful litigation by NRDC in 1976 (43 FR 46258). The 1977 CAA Amendments created a process for regular review of the NAAQS list, and created a permanent independent scientific review committee to provide technical input on the NAAQS to EPA.[5] EPA added regulations for PM2.5 in 1997 (62 FR 38652), and updates the NAAQS from time to time based on emerging environmental and health science.

National Emissions Standards for Hazardous Air Pollutants (NESHAPs)

The NESHAPs govern how much of 187 toxic air pollutants are allowed to be emitted from industrial facilities and other sources. [6] Under the CAA, hazardous air pollutants (HAPs, or air toxics) are air pollutants other than those for which NAAQS exist, which threaten human health and welfare. The NESPHAPs are the standards used for controlling, reducing, and eliminating HAPs emissions from stationary sources such as industrial facilities. The 1970 CAA required EPA to develop a list of HAPs, and then develop national emissions standards for each of them. The original NESHAPs were health-based standards. The 1990 CAA Amendments (Pub.L. 101-549 Title III) codified EPA's list, and required creation of technology-based standards according to "maximum achievable control technology" (MACT). Over the years, EPA has issued dozens of NESHAP regulations, which have developed NESHAPs by pollutant, by industry source category, and by industrial process. There are also NESHAPs for mobile sources (transportation), although these are primarily handled under the mobile source authorities.[7] The 1990 amendments (adding CAA § 112(d-f)) also created a process by which EPA was required to review and update its NESHAPs every eight years, and identify any risks remaining after application of MACT, and develop additional rules necessary to protect public health.[8]

New Source Performance Standards (NSPS)

The NSPS are rules for the equipment required to be installed in new and modified industrial facilities, and the rules for determining whether a facility is "new."[9] The 1970 CAA required EPA to develop standards for newly-constructed and modified stationary sources (industrial facilities) using the "best system of emission reduction which (taking into account the cost of achieving such reduction) the [EPA] determines has been adequately demonstrated." EPA issued its first NSPS regulation the next year, covering steam generators, incinerators, Portland cement plants, and nitric and sulfuric acid plants (36 FR 24876). Since then, EPA has issued dozens of NSPS regulations, primarily by source category. The requirements promote industrywide adoption of available pollution control technologies. However, because these standards apply only to new and modified sources, they promote extending the lifetimes of pre-existing facilities. In the 1977 CAA Amendments, Congress required EPA to conduct a "new source review" process (40 CFR 52, subpart I) to determine whether maintenance and other activities rises to the level of modification requiring application of NSPS.[10]

Acid Rain Program (ARP)

The ARP is an emissions trading program for power plants to control the pollutants that cause acid rain. [11] The 1990 CAA Amendments created a new title to address the issue of acid rain, and particularly nitrogen oxides (NOx) and sulfur dioxide (SO2) emissions from electric power plants powered by fossil fuels, and other industrial sources. The Acid Rain Program was the first emissions trading program in the United States, setting a cap on total emissions that was reduced over time by way of traded emissions credits, rather than direct controls on emissions. The program evolved in two stages: the first stage required more than 100 electric generating facilities larger than 100 megawatts to meet a 3.5 million ton SO2 emission reduction by January 1995. The second stage gave facilities larger than 75 megawatts a January 2000 deadline. The program has achieved all of its statutory goals.[12]

Ozone Layer Protection

The CAA ozone program is a technology transition program intended to phase out the use of chemicals that harm the ozone layer.[13] Consistent with the US commitments in the Montreal Protocol, CAA Title VI, added by the 1990 CAA Amendments, mandated regulations regarding the use and production of chemicals that harm Earth's stratospheric ozone layer. Under Title VI, EPA runs programs to phase out ozone-destroying substances, track their import and export, determine exemptions for their continued use, and define practices for destroying them, maintaining and servicing equipment that uses them, and identifying new alternatives to those still in use.

Mobile Source Programs

Rules for pollutants emitted from internal combustion engines in vehicles.[14] Since 1965, Congress has mandated increasingly stringent controls on vehicle engine technology and reductions in tailpipe emissions. Today, the law requires EPA to establish and regularly update regulations for pollutants that may threaten public health, from a wide variety of classes of motor vehicles, that incorporate technology to achieve the "greatest degree of emission reduction achievable," factoring in availability, cost, energy, and safety (42 U.S.C. § 7521).

Onroad vehicles regulations

EPA sets standards for exhaust gases, evaporative emissions, air toxics, refueling vapor recovery, and vehicle inspection and maintenance for several classes of vehicles that travel on roadways. EPA's "light-duty vehicles" regulations cover passenger cars, minivans, passenger vans, pickup trucks, and SUVs. "Heavy-duty vehicles" regulations cover large trucks and buses. EPA first issued motorcycle emissions regulations in 1977 (42 FR 1122) and updated them in 2004 (69 FR 2397).

Nonroad vehicles regulations

The 1970 CAA amendments provided for regulation of aircraft emissions (42 U.S.C. § 7571), and EPA began regulating in 1973. In 2012, EPA finalized its newest restrictions on NOx emissions from gas turbine aircraft engines with rated thrusts above 26.7 kiloNewton (3 short ton-force), meaning primarily commercial jet aircraft engines, intended to match international standards. EPA has been investigating whether to regulate lead in fuels for small aircraft since 2010, but has not yet acted. The 1990 CAA Amendments (Pub.L. 101-549 § 222) added rules for a "nonroad" engine program (42 U.S.C. § 7547), which expanded EPA regulation to locomotives, heavy equipment and small equipment engines fueled by diesel (compression-ignition), and gas and other fuels (spark-ignition), and marine transport.

Voluntary programs

EPA has developed a variety of voluntary programs to incentivize and promote reduction in transportation-related air pollution, including elements of the Clean Diesel Campaign, Ports Initiative, SmartWay program, and others.

Fuel Controls

EPA has regulated the chemical composition of transportation fuels since 1967, with significant new authority added in 1970 to protect public health. [15] One of EPA's earliest actions was the elimination of lead in U.S. gasoline beginning in 1971 (36 FR 1486, 37 FR 3882, 38 FR 33734), a project that has been described as "one of the great public health achievements of the 20th century."[16] EPA continues to regulate the chemical composition of gasoline, avgas, and diesel fuel in the United States.

State Implementation Plans (SIPs)

Since its earliest version in 1963, the Clean Air Act has set up a cooperative federalist program for developing pollution control standards and programs.[17]Rather than create an entirely federal system, the CAA imposes responsibilities on the U.S. states to create plans to implement the Act's requirements. EPA then reviews, amends, and approves those plans. EPA first promulgated SIP regulations in 1971 and 1972 (36 FR 15486, 37 FR 19807).

Nonattainment Areas

The 1977 CAA Amendments added SIP requirements for areas that had not attained the applicable NAAQS ("nonattainment areas"). In these areas, states were required to adopt plans that made "reasonable further progress" toward attainment until all all "reasonably available control measures" could be adopted. As progress on attainment was much slower than Congress originally instructed, major amendments to SIP requirements in nonattainment areas were part of the 1990 CAA Amendments.[18]

Prevention of Significant Deterioration (PSD

(40 CFR 52.21). The 1977 CAA Amendments (Pub.L. 95-95 section 127, adding CAA Title I Part C, codified 42 U.S.C. ch. 85, subch. I), modified the SIP requirements to protect areas - including particularly wilderness areas and national parks - that already met the NAAQS; that is, to require SIPs to preserve good air in addition to cleaning up bad air. The new law also required New Source Review (investigations of proposed construction of new polluting facilities) to examine whether PSD requirements would be met.

Title V Permitting

The 1990 amendments authorized a national operating permit program, covering thousands of large industrial and commercial sources.[19] It required large businesses to address pollutants released into the air, measure their quantity, and have a plan to control and minimize them as well as to periodically report. This consolidated requirements for a facility into a single document.[19] In non-attainment areas, permits were required for sources that emit as little as 50, 25, or 10 tons per year of VOCs depending on the severity of the region's non-attainment status.[20] Most permits are issued by state and local agencies.[21] If the state does not adequately monitor requirements, the EPA may take control. The public may request to view the permits by contacting the EPA. The permit is limited to no more than five years and requires a renewal.[20]

Monitoring and Enforcement

One of the most public aspects of the Clean Air Act, EPA is empowered to monitor compliance with the law's many requirements, seek penalties for violations, and compel regulated entities to come into compliance.[22] Enforcement cases are usually settled, with penalties assessed well below maximum statutory limits. Recently, many of the largest Clean Air Act settlements have been reached with automakers accused of circumventing the Act's vehicle and fuel standards (e.g., Dieselgate).

Greenhouse Gas Regulation

Much of EPA's regulation of greenhouse gas emissions in the United States occurs under the programs discussed above. EPA began regulating GHG emissions following the Supreme Court's ruling in Massachusetts v. EPA, the EPA's subsequent endangerment finding, and development of specific regulations for various sources.[23] Standards for mobile sources have been established pursuant to Section 202 of the CAA, and GHGs from stationary sources are controlled under the authority of Part C of Title I of the Act. The EPA's auto emission standards for greenhouse gas emissions issued in 2010 and 2012 are intended to cut emissions from targeted vehicles by half, double fuel economy of passenger cars and light-duty trucks by 2025 and save over $4 billion barrels of oil and $1.7 trillion for consumers. The agency has also proposed a two-phase program to reduce greenhouse gas emissions for medium and heavy duty trucks and buses.[24] In addition, EPA oversees the national greenhouse gas inventory reporting program.[25]


Other important but less foundational Clean Air Act regulatory programs tend to build on or cut across the above programs:

  • Risk Assessment.[26] Although not a regulatory program per se, many EPA regulatory programs involve risk assessment and management. Over the years, EPA has undertaken to unify and organize its many risk assessment processes. The 1990 CAA Amendments created a Commission on Risk Assessment and Management tasked with making recommendations for a risk assessment framework,[27] and many subsequent reports have built on this work.
  • Visibility and Regional Haze.[28] EPA monitors visibility and air clarity (haze) at 156 protected parks and wilderness areas, and requires states to develop plans to improve visibility by reducing pollutants that contribute to haze.
  • Interstate pollution control.[29] The Clean Air Act's "good neighbor" provision requires states to control emissions that will significantly contribute to NAAQS nonattainment or maintenance in a downwind state.[30] EPA has struggled to enact regulations that implement this requirement for many years. It developed the "Clean Air Interstate Rule" between 2003 and 2005, but this was overturned by the courts in 2008. EPA then developed the Cross-State Air Pollution Rule between 2009 and 2011, and it continues to be litigated as EPA updates it.
  • Startup, Shutdown, & Malfunction. EPA promulgates rules for states to address excess emissions during periods of startup, shutdown, and malfunction, when facility emissions may temporarily be much higher than standard regulatory limits.[31]


Between the Second Industrial Revolution and the 1960s, the United States experienced increasingly severe air pollution. Following the 1948 Donora smog event, the public began to discuss air pollution as a major problem, states began to pass a series of laws to reduce air pollution, and Congress began discussing whether to take further action in response. At the time, the primary federal agencies interested in air pollution were the United States Bureau of Mines, which was interested in "smoke abatement" (reducing smoke from coal burning), and the United States Public Health Service, which handled industrial hygiene and was concerned with the causes of lung health problems.[32]

After several years of proposals and hearings, Congress passed the first federal legislation to address air pollution in 1955. The Air Pollution Control Act of 1955 authorized a research and training program, sending $3 million per year to the U.S. Public Health Service for five years, but did not directly regulate pollution sources. The 1955 Act's research program was extended in 1959, 1960, and 1962 while Congress considered whether to regulate further.

Beginning in 1963, Congress began expanding federal air pollution control law to accelerate the elimination of air pollution throughout the country. The new law's programs were initially administered by the U.S. Secretary of Health, Education, and Welfare, and the Air Pollution Office of the U.S. Public Health Service, until they were transferred to the newly-created EPA immediately before major amendments in 1970. EPA has administered the Clean Air Act ever since, and Congress added major regulatory programs in 1977 and 1990.[33] Most recently, the U.S. Supreme Court's ruling in Massachusetts v. EPA resulted in an expansion of EPA's CAA regulatory activities to cover greenhouse gases.

Clean Air Act of 1963 and Early Amendments. The Clean Air Act of 1963 (Pub.L. 88-206) was the first federal legislation to permit the U.S. federal government to take direct action to control air pollution. It extended the 1955 research program, encouraged cooperative state, local, and federal action to reduce air pollution, appropriated $95 million over three years to support the development of state pollution control programs, and authorized the HEW Secretary to organize conferences and take direct action against interstate air pollution where state action was deemed to be insufficient.[32]

The Motor Vehicle Air Pollution Control Act (Pub.L. 89-272) amended the 1963 Clean Air Act and set the first federal vehicle emissions standards, beginning with the 1968 models. These standards were reductions from 1963 emissions levels: 72% reduction for hydrocarbons, 56% reduction for carbon monoxide, and 100% reduction for crankcase hydrocarbons.[]. The law also added a new section to authorize abatement of international air pollution.[34]

President Lyndon B. Johnson signing the 1967 Air Quality Act in the East Room of the White House, November 21, 1967.

The Air Quality Act of 1967 (Pub.L. 90-148) authorized planning grants to state air pollution control agencies, permitted the creation of interstate air pollution control agencies, and required HEW to define air quality regions and develop technical documentation that would allow states to set ambient air quality and pollution control technology standards, and required states to submit implementation plans for improvement of air quality, and permitted HEW to take direct abatement action in air pollution emergencies. It also authorized expanded studies of air pollutant emission inventories, ambient monitoring techniques, and control techniques.[35][34] This enabled the federal government to increase its activities to investigate enforcing interstate air pollution transport, and, for the first time, to perform far-reaching ambient monitoring studies and stationary source inspections. The 1967 act also authorized expanded studies of air pollutant emission inventories, ambient monitoring techniques, and control techniques.[36] While only six states had air pollution programs in 1960, all 50 states had air pollution programs by 1970 due to the federal funding and legislation of the 1960s.[24]

President Richard Nixon signs the Clean Air Amendments of 1970 at the White House, December 31, 1970.

1970 Amendments. In the Clean Air Amendments of 1970 (Pub.L. 91-604), Congress greatly expanded the federal mandate by requiring comprehensive federal and state regulations for both industrial and mobile sources. The law established the National Ambient Air Quality Standards (NAAQS), New Source Performance Standards (NSPS); and National Emissions Standards for Hazardous Air Pollutants (NESHAPs), and significantly strengthened federal enforcement authority, all toward achieving aggressive air pollution reduction goals.

To implement the strict amendments, EPA Administrator William Ruckelshaus spent 60% of his time during his first term on the automobile industry, whose emissions were to be reduced 90% under the new law. Senators had been frustrated at the industry's failure to cut emissions under previous, weaker air laws.[37]

1977 Amendments. Major amendments were added to the Clean Air Act in 1977 (1977 CAAA) (91 Stat. 685, Pub.L. 95-95). The 1977 Amendments primarily concerned provisions for the Prevention of Significant Deterioration (PSD) of air quality in areas attaining the NAAQS. The 1977 CAAA also contained requirements pertaining to sources in non-attainment areas for NAAQS. A non-attainment area is a geographic area that does not meet one or more of the federal air quality standards. Both of these 1977 CAAA established major permit review requirements to ensure attainment and maintenance of the NAAQS.[36] These amendments also included the adoption of an offset trading policy originally applied to Los Angeles in 1974 that enables new sources to offset their emissions by purchasing extra reductions from existing sources.[24]

The Clean Air Act Amendments of 1977 required Prevention of Significant Deterioration (PSD) of air quality for areas attaining the NAAQS and added requirements for non-attainment areas.[38]

President George H. W. Bush signs the Clean Air Act Amendments of 1990 at the White House, November 15, 1990.

1990 Amendments. Another set of major amendments to the Clean Air Act occurred in 1990 (1990 CAAA) (104 Stat. 2468, Pub.L. 101-549). The 1990 CAAA substantially increased the authority and responsibility of the federal government. New regulatory programs were authorized for control of acid deposition (acid rain)[39] and for the issuance of stationary source operating permits. The NESHAPs were incorporated into a greatly expanded program for controlling toxic air pollutants. The provisions for attainment and maintenance of NAAQS were substantially modified and expanded. Other revisions included provisions regarding stratospheric ozone protection, increased enforcement authority, and expanded research programs.[36]

The 1990 Clean Air Act added regulatory programs for control of acid deposition (acid rain) and stationary source operating permits. The provisions aimed at reducing sulfur dioxide emissions included a cap-and-trade program, which gave power companies more flexibility in meeting the law's goals compared to earlier iterations of the Clean Air Act.[40] The amendments moved considerably beyond the original criteria pollutants, expanding the NESHAP program with a list of 189 hazardous air pollutants to be controlled within hundreds of source categories, according to a specific schedule.[41] The NAAQS program was also expanded. Other new provisions covered stratospheric ozone protection, increased enforcement authority and expanded research programs.[42]

Further amendments were made in 1990 to address the problems of acid rain, ozone depletion, and toxic air pollution, and to establish a national permit program for stationary sources, and increased enforcement authority. The amendments also established new auto gasoline reformulation requirements, set Reid vapor pressure (RVP) standards to control Evaporative emissions from gasoline, and mandated new gasoline formulations sold from May to September in many states. Reviewing his tenure as EPA Administrator under President George H. W. Bush, William K. Reilly characterized passage of the 1990 amendments to the Clean Air Act as his most notable accomplishment.[43]

Federalism. Before 1970, there was only a very limited national air pollution control program, with almost all enforcement authority reserved to state and local governments, as had been the case traditionally under U.S. federalism. The 1970 Clean Air Act was a major evolution in this system, providing the U.S. EPA with enforcement authority and requiring states to develop State Implementation Plans for how they would meet new national ambient air quality standards by 1977.[44] This cooperative federal model continues today. The law recognizes that states should lead in carrying out the Clean Air Act, because pollution control problems often require special understanding of local industries, geography, housing patterns, etc. However, states are not allowed to have weaker controls than the national minimum criteria set by EPA. EPA must approve each SIP, and if a SIP is not acceptable, EPA can retain CAA enforcement in that state. For example, California was unable to meet the new standards set by the Clean Air Act of 1970, which led to a lawsuit and a federal state implementation plan for the state.[45] The federal government also assists the states by providing scientific research, expert studies, engineering designs, and money to support clean air programs. The law also prevents states from setting standards that are more strict than the federal standards, but carves out a special exemption for California due to its past issues with smog pollution in the metropolitan areas. In practice, when California's environmental agencies decide on new vehicle emission standards, they are submitted to the EPA for approval under this waiver, with the most recent approval in 2009.[46] The California standard was adopted by twelve other states, and established the de facto standard that automobile manufacturers subsequently accepted, to avoid having to develop different emission systems in their vehicles for different states. However, in September 2019, President Donald Trump attempted to revoke this waiver, arguing that the stricter emissions have made cars too expensive, and by removing them, will make vehicles safer. EPA's Andrew Wheeler also stated that while the agency respects federalism, they could not allow one state to dictate standards for the entire nation. California's governor Gavin Newsom considered the move part of Trump's "political vendetta" against California and stated his intent to sue the federal government.[47] Twenty-three states, along with the District of Columbia and the cities of New York City and Los Angeles joined California in a federal lawsuit challenging the administration's decision.[48]


Graph showing decreases in US air pollution concentrations during 1990 to 2015

According to the most recent study by EPA, when compared to the baseline of the 1970 and 1977 regulatory programs, by 2020 the updates initiated by the 1990 Clean Air Act Amendments would be costing the United States about $60 billion per year, while benefiting the United States (in monetized health and lives saved) about $2 trillion per year.[49] In 2020, a study prepared for the Natural Resources Defense Council estimated annual benefits at 370,000 avoided premature deaths, 189,000 fewer hospital admissions, and net economic benefits of up to $3.8 trillion (32 times the cost of the regulations).[50] Other studies have reached similar conclusions.[51]

Mobile sources including automobiles, trains, and boat engines have become 99% cleaner for pollutants like hydrocarbons, carbon monoxide, nitrogen oxides, and particle emissions since the 1970s. The allowable emissions of volatile organic chemicals, carbon monoxide, nitrogen oxides, and lead from individual cars have also been reduced by more than 90%, resulting in decreased national emissions of these pollutants despite a more than 400% increase in total miles driven yearly.[24] Since the 1980s, 1/4th of ground level ozone has been cut, mercury emissions have been cut by 80%, and since the change from leaded gas to unleaded gas 90% of atmospheric lead pollution has been reduced.[52] A 2018 study found that the Clean Air Act contributed to the 60% decline in pollution emissions by the manufacturing industry between 1990 and 2008.[53][54]

Future challenges

As of 2017, some US cities still do not meet all national ambient air quality standards. It is likely that tens of thousands of premature deaths are still being caused by fine-particle pollution and ground-level ozone pollution.[24]

Climate change poses a challenge to the management of conventional air pollutants in the United States due to warmer, dryer summer conditions that can lead to increased air stagnation episodes. Prolonged droughts that may contribute to wildfires would also result in regionally high levels of air particles.[55]

Transboundary air pollution (both entering and exiting the United States) is not directly regulated by the Clean Air Act, requiring international negotiations and ongoing agreements with other nations, particularly Canada and Mexico.[56]

Environmental justice continues to be an ongoing challenge for the Clean Air Act. By promoting pollution reduction, the Clean Air Act helps reduce heightened exposure to air pollution among communities of color and low-income communities.[57] But African American populations are "consistently over represented" in areas with the poorest air quality.[58] Dense populations of low-income and minority communities inhabit the most polluted areas across the United States, which is considered to exacerbate health problems among these populations.[59] High levels of exposure to air pollution is linked to several health conditions, including asthma, cancer, premature death, and infant mortality, each of which disproportionately impact communities of color and low-income communities.[60] The pollution reduction achieved by the Clean Air Act is associated with a decline in each of these conditions and can promote environmental justice for communities that are disproportionately impacted by air pollution and diminished health status.[60]


  1. ^ "The Plain English Guide to the Clean Air Act". Clean Air Act Overview. Washington, D.C.: US Environmental Protection Agency (EPA). April 2007.
  2. ^ U.S. EPA (May 29, 2015). "CAA Section Correspondence Tables".
  3. ^ 40 C.F.R. "Subchapter C (Air Programs)".
  4. ^ NAAQS Program:
  5. ^ See "EPA Clean Air Scientific Advisory Committee".
  6. ^ NESHAPS Program:
  7. ^ U.S. EPA (August 3, 2016). "HAPs Mobile Source Rule".
  8. ^ U.S. EPA (December 15, 2016). "NESHAPs Risk and Technology Review".
  9. ^ NSPS Program:
  10. ^ U.S. EPA (December 9, 2015). "NSR Regulatory Actions".
  11. ^ Acid Rain Program:
  12. ^ U.S. EPA. "ARP Progress Reports".
  13. ^ Ozone Layer Protection Program:
  14. ^ Mobile Source Programs
  15. ^ Fuel Controls Programs:
  16. ^ Bridbord, Kenneth; Hanson, David (August 2009). "A Personal Perspective on the Initial Federal Health-Based Regulation to Remove Lead from Gasoline". Environmental Health Perspectives. 117 (8): 1195-1201. doi:10.1289/ehp.0800534. PMC 2721861. PMID 19672397.
  17. ^ 40 CFR 51, 40 CFR 52
  18. ^ Garrett & Winner. "Chapter 4. Nonattainment". ELR.
  19. ^ a b EPA. "Permits and Enforcement." The Plain English Guide to the Clean Air Act. Revised November 8, 2011.
  20. ^ a b McCarthy, James (February 25, 2020). "Clean Air Act: A Summary of the Act and its Major Requirements". CRS Report for Congress. Retrieved 2021.
  21. ^ EPA (February 1998). "Air Pollution Operating Permit Program Update: Key Features and Benefits." Document no. EPA/451/K-98/002. p. 1.
  22. ^ Monitoring and Enforcement EPA pages: U.S. EPA. "CAA Compliance Monitoring"., "Air Enforcement"., "Air Enforcement Policy, Guidance and Publications"., "Enforcement Data and Results".
  23. ^ Environmental Protection Agency. "Fact Sheet: Clean Air Act Permitting for Greenhouse Gas Emissions - Final Rules" (PDF). EPA. Retrieved 2018.
  24. ^ a b c d e John Bachmann, David Calkins, Margo Oge. "Cleaning the Air We Breathe: A Half Century of Progress." EPA Alumni Association. September 2017.
  25. ^ U.S. EPA. "Greenhouse Gas Reporting Program".
  26. ^ U.S. EPA. "Risk Assessment". "History of Risk Assessment at EPA".
  27. ^ Pub.L. 101-549 § 303. Not codified.
  28. ^ Regional Haze Program:
  29. ^ U.S. EPA. "Interstate Air Pollution Transport". Kate C., Shouse. "The Clean Air Act's Good Neighbor Provision: Overview of Interstate Air Pollution Control" (PDF). U.S. EPA. "Clean Air Interstate Rule (Archive)".
  30. ^ 42 U.S.C. § 7410(a)(2)(D)(i)(I)/
  31. ^ U.S. EPA. "Emissions During Periods of Startup, Shutdown, & Malfunction (SSM)".
  32. ^ a b Orford, Adam (2021). "The Clean Air Act of 1963: Postwar Environmental Politics and the Debate Over Federal Power". Hastings Environmental Law Journal. 27 (2): 1-77. ISSN 1080-0735. Retrieved 2021.
  33. ^ Bailey, Christopher J. (1998). Congress and Air Pollution. Manchester University Press.
  34. ^ a b Stern, Arthur C. (1982). "History of Air Pollution Legislation in the United States". Journal of the Air Pollution Control Association. 32 (1): 44-61. doi:10.1080/00022470.1982.10465369. PMID 7033323.
  35. ^ "The Air Quality Act of 1967". Journal of the Air Pollution Control Association. 18:2 (2): 62-71. 1968. doi:10.1080/00022470.1968.10469096. PMID 5637413.
  36. ^ a b c Public Domain This article incorporates public domain material from the United States Government document: "History of the Clean Air Act, U.S. Environmental Protection Agency"."History of the Clean Air Act". Environmental Protection Agency. August 8, 2013. Retrieved 2014.
  37. ^ EPA Alumni Association: William Ruckelshaus in a 2013 interview discusses his first-term efforts at implementing the Clean Air Act of 1970, Video, Transcript (see p14).
  38. ^ Clean Air Act Amendments of 1977, P.L. 95-95, 91 Stat. 685, August 7, 1977.
  39. ^ Former Deputy Administrator Hank Habicht talks about management at EPA. An Interview with Hank Habicht Video, Transcript (see p6). December 21, 2012.
  40. ^ Turner, James Morton; Isenberg, Andrew C. (2018). The Republican Reversal: Conservatives and the Environment from Nixon to Trump. Harvard University Press. pp. 119-120. ISBN 978-0674979970.
  41. ^ EPA. "Reducing Toxic Air Pollutants." The Plain English Guide to the Clean Air Act. Revised November 8, 2011.
  42. ^ Clean Air Act Amendments of 1990, P.L. 101-549, 104 Stat. 2399, November 15, 1990.
  43. ^ EPA Alumni Association: EPA Administrator William K. Reilly describes why passage of the 1990 Clean Air Act amendments was vitally important. Reflections on US Environmental Policy: An Interview with William K. Reilly Video, Transcript (see p10).
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