Clean Air Act (U.S.)

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(PD) Photo: Jon Sullivan,
Poor air quality over Los Angeles (August, 2003)
See also: National Ambient Air Quality Standards

The Clean Air Act is a law enacted by the U.S. Congress that defines the responsibilities of the U.S. Environmental Protection Agency (U.S. EPA) for protecting and improving the nation's air quality and the stratospheric ozone layer. The latest major amendments were enacted as the Clean Air Act Amendments of 1990 (Public Law 101–549).

The Clean Air Act Amendments of 1990 were preceded by various other pieces of legislation enacted by the U.S. Congress dating back to the Air Pollution Control Act of 1955.

Implementation of the Act

In the same year that Congress created the Clean Air Act of 1970 (see History section below), Congress also created the U.S. EPA and gave it the primary role in carrying out the law. Since 1970, the U.S. EPA has been responsible for a variety of programs to reduce air pollution nationwide.

However, the environmental regulatory agencies of the states, Indian tribes and local governments do a lot of the work to meet the Act's requirements. Those agencies work with industrial and commercial companies to reduce air pollution. They also review and approve permit applications for construction and operation of industrial plants and commercial facilities involving sources of air pollution. They are able to develop solutions for pollution problems that require special understanding of local industries, geography, housing, and travel patterns, as well as other factors. State, local, and tribal governments also monitor air quality, inspect facilities under their jurisdictions and enforce Clean Air Act regulations.[1]

States must also develop State Implementation Plans (SIPs) that outline how each state will control air pollution under the Clean Air Act. An SIP is a collection of the regulations, programs and policies that a state will use to clean up polluted areas. In developing their SIPs, the states must involve the public and industries through hearings and opportunities to comment on the development of each state plan.[1]

Contents of the Act

Legislation enacted by the U.S. Congress since 1990 has made several minor changes in the Act. The current version, including amendments through February 24, 2004, is available on the Internet.[2] This is a listing of its major parts:

  • Title I - Air Pollution Prevention and Control
    • Part A - Air Quality and Emission Limitations (CAA § 101-131; USC § 7401-7431 )
    • Part B - Ozone Protection (replaced by Title VI)
    • Part C - Prevention of Significant Deterioration of Air Quality (CAA § 160-169b; USC § 7470-7492)
    • Part D - Plan Requirements for Nonattainment Areas (CAA § 171-193; USC § 7501-7515)
  • Title II - Emission Standards for Moving Sources
    • Part A - Motor Vehicle Emission and Fuel Standards (CAA § 201-219; USC § 7521-7554)
    • Part B - Aircraft Emission Standards (CAA § 231-234; USC § 7571-7574)
    • Part C - Clean Fuel Vehicles (CAA § 241-250; USC § 7581-7590)
  • Title III - General (CAA § 301-328; USC § 7601-7627)
  • Title IV - Acid Deposition Control (CAA § 401-416; USC § 7651-7651o)
  • Title V - Permits (CAA § 501-507; USC § 7661-7661f )
  • Title VI - Stratospheric Ozone Protection (CAA § 601-618; USC § 7671-7671q )

Key elements of the act

The U.S. EPA's mission is to protect human health and the environment. To achieve this mission, EPA implemented a variety of programs under the Clean Air Act that focus on:

  • Reducing outdoor ambient concentrations of air pollutants that cause smog, haze, acid rain, and other problems
  • Reducing emissions of toxic air pollutants that are known to, or are suspected of, causing cancer or other serious health effects
  • Phasing out production and use of chemicals that destroy stratospheric ozone.

The above programs have required the development of specific regulations by the U.S. EPA and the state, tribal and local governments to limit the emissions of air pollutants from mobile sources (like automotive vehicles and airplanes) and stationary sources (like petroleum refineries, petrochemical and chemical manufacturing plants, power plants, and gas or petrol stations).

More specifics concerning each of the above programs are available on the Internet.[3]

What the Clean Air Act has accomplished

The implementation of the Clean Air Act has accomplished very significant reductions in the emission of air pollutants during the period of 1970 – 2008. The reductions were accomplished despite even larger increases in activities, during that same period, that produce air pollutants as measured by the national Gross Domestic Product (GDP), consumption of energy, and usage of automobiles. The details of that accomplishment are presented in the two tables below:[1][4]

Air pollutant emission reductions
(1970 – 2008)
Pollutant Emissions Reductions
Criteria air pollutants More than 50%
Toxic air pollutants Nearly 70%
Automobile emissions More than 90%
Activities that produce air pollutants
(1970 – 2008)
Factors Increases
Gross Domestic Product 200 %
Energy consumption 50%
Automobile usage Almost 200%


In October 1948, a cloud of air pollution formed above the industrial town of Donora, Pennsylvania and lingered for five days. It caused sickness in 6,000 of the town's 14,000 people and the death of 20 people. Four years later, in 1952, over 3,000 people died in what became known as London's "Killer Fog".[1][4] Events like those led to the enactment of several federal and state laws which established funding for the study and the cleanup of air pollution. But there was no comprehensive federal response to address air pollution until Congress passed the Clean Air Act in 1970 and created the U.S. EPA.

In 1990, Congress amended and greatly expanded the Clean Air Act, providing EPA even broader authority to implement and enforce regulations reducing air pollutant emissions. The 1990 Amendments also placed an increased emphasis on more cost-effective approaches to reduce air pollution.

The principal milestones in the evolution of the Clean Air Act are:[4][5][6]

The Air Pollution Control Act of 1955

The Air Pollution Control Act of 1955 was the first federal legislation that involved air pollution. It funded research of air pollution and state assistance resources.

Clean Air Act of 1963

The Clean Air Act of 1963 was the first federal legislation regarding air pollution control. It established a federal program within the U.S. Public Health Service and authorized research into techniques for monitoring and controlling air pollution. It included grants to the states for developing state and local air pollution control programs.

In 1966, the Clean Air Act was extended to add the authority for grants to maintain state and local programs rather than just develop them.

Air Quality Act of 1967

In 1967, an Air Quality Act was enacted in order to expand federal government activities. In accordance with this law, enforcement proceedings were initiated in areas subject to interstate air pollution transport. As part of these proceedings, the federal government for the first time conducted extensive ambient monitoring studies and stationary source inspections.

The Air Quality Act of 1967 also authorized expanded studies of air pollutant emission inventories, ambient monitoring techniques, and control techniques.

Clean Air Act 1970

The enactment of the Clean Air Act of 1970 constituted a major change of the federal government's role in air pollution control. It authorized the development of comprehensive federal and state regulations to limit emissions from stationary industrial sources and from mobile sources.

Four major regulatory programs involving stationary sources were initiated:

It also authorized requirements for the control of automotive vehicle emissions (i.e., mobile sources). Furthermore, the authority to enforce air quality standards and air pollution emission controls was substantially expanded.

As mentioned above, the EPA was created at about the same time in order to implement the various requirements included in the Clean Air Act of 1970.

1977 Amendments to the Clean Air Act of 1970

The 1977 Amendments established major review requirements to ensure the attainment and maintenance of the National Ambient Air Quality Standards.

It codified provisions for the Prevention of Significant Deterioration (PSD) program. It also codified requirements pertaining to air pollution sources in geographical areas called "non-attainment areas" because they had not attained on or more of the National Ambient Air Quality Standards.

1990 Amendments to the Clean Air Act of 1970

Another set of major amendments to the Clean Air Act were enacted in 1990 that substantially increased the authority and responsibility of the federal government. New regulatory programs were authorized for:

  • Control of acid deposition (acid rain)
  • Established the requirements for stationary source operating permits
  • Established a program to control 189 toxic air pollutants, including those previously regulated by the National Emission Standards for Hazardous Air Pollutants (NESHAPS)

The provisions for attainment and maintenance of the National Ambient Air Quality Standards were significantly modified and expanded. Other revisions involved stratospheric ozone protection, increased enforcement authority, and expanded research programs.


  1. 1.0 1.1 1.2 1.3 Understanding the Clean Air Act (From the U.S. EPA website)
  2. The Clean Air Act (As Amended Through P.L. 108–201, February 24, 2004)
  3. Key Elements of the Clean Air Act (From the U.S. EPA website)
  4. 4.0 4.1 4.2 Air Today, Yesterday, and Tomorrow (Part 1, prepared for the U.S. EPA by John Bachmann, 2008)
  5. Air Today, Yesterday, and Tomorrow (Part 2, prepared for the U.S. EPA by John Bachmann, 2008)
  6. History of the Clean Air Act (From the U.S. EPA website)