Clean Air Act: An Overview

Background and Statutory Framework

The Clean Air Act (“CAA”) seeks “to protect and enhance the quality of the Nation’s air resources so as to promote the public health and welfare and the productive capacity of its population.” 42 U.S.C. § 7401. The CAA was originally enacted in 1955 and was amended in 1970, 1977, and 1990 as an effort to protect the nation’s air quality. 42 U.S.C. 7401–7671q. Prior to 1955, air pollution was the exclusive responsibility of state and local levels of government. The 1970 amendments established the procedures under which the EPA sets national standards for ambient air quality, required a 90% reduction in emissions from new autombiles by 1975, established a program to require the best avialble 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 standarads, and added the Prevention of Significant Deterioration program to protect air cleaner than national standards. 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 statuts; (2) tighten auto and other mobile source emission standards; (3) require reformulated and alternative fuesl 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 markatble allowance scheme to provide flexibility in implementation; (6) require a state-run permit program for the opertation of major sources of air pollutants; (7) implement the Montreal Protcol 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 admisnitrative penalites. In addition, the 1990 amendments authorized appropriations for clean air programs through FY1998.  The Act provides a comprehensive and complex regulatory framework for regulating stationary and mobile sources of air pollution, their fuels, 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 requires the Environmental Protection Agency (“EPA”) to establish minimum national standards for air quality and assigns primary responsibility for enforcement and compliance to the states. The Act also establishes a permit system for all major sources of pollution and addresses prevention of pollution in areas with clean air.

National Ambient Air Quality Standards

The CAA requires the EPA to establish National Ambient Air Quality Standards (“NAAQS”) for pollutants that the EPA determines endanger public health or welfare. 42 U.S.C. § 7409. The NAAQS are designed to protect public health with an adequate margin of safety and to protect the public welfare from any known or anticipated adverse effects. Under this authority, the EPA has established NAAQS for six different air pollutants: sulfur dioxide (SO2), particulate matter (PM2.5 and PM10), nitrogen dioxide (NO2), carbon monoxide (CO), ozone, and lead. Every state must comply with the regulations set forth by the EPA for each of these pollutants. The act requires EPA to review the scientific data upon which the standards are based every five years, and revise the standards, when necessary.

State Implementation Plans (SIPs)

To carry out the regulations set by the EPA, states develop State Implementation Plans (“SIPs”) and must submit those plans to the EPA for approval. 42 U.S.C. § 7410.  Once approved, the SIPs carry the force of federal law, and the states must comply with the approved standards.  States develop SIPs based on emission inventories and computer models to determine whether air quality violations will occur.  If the data show that the standards are exceeded, then the states must impose additional controls to conform to the regulations. The EPA must approve any deviation or change in an existing SIP. Ultimately, a Federal Implementation Plan may be imposed if the state fails to submit or implement an adequate SIP.

Nonattainment Areas

Areas not meeting the required standards, known as “nonattainment areas”, are subject to stricter EPA enforcement procedures.  The CAA classifies nonattainment areas based on the extent to which the area exceeds NAAQS.  The Act sets forth specific pollution controls and attainment dates for each classification. 42 U.S.C. §§ 7501–7515.


Other Major Provisions

Other major provisions of the CAA include

    • Transported Air Pollution, 42 U.S.C. § 7410(a)(2)(D)
      • Ensures that the SIPs include adequate provisions to prevent sources from within the state from polluting downwind states.
  • Emission Standards for Mobile Sources, 42 U.S.C. § 7408
  • Hazardous Air Pollutants, 42 U.S.C. § 7412
  • New Source Performance Standards, 42 U.S.C. § 7411
      • Requires the EPA to establish national standards for categories of new industrial facilities.
  • Prevention of Significant Deterioration of Air Quality, 42 U.S.C. §§ 7470–79
  • Permits, 42 U.S.C. §§ 7502–03
      • Requires states to administer a permit program for the operation of sources emitting air pollutants.

Links to these provisions are located in the Reading Room


Since the Act emphasizes controlling “major sources” that emit more than the threshold of regulated pollutants, emissions from most farms usually do not exceed the specified threshold and are therefore exempt from most CAA regulatory programs.  However, agricultural sources are not totally exempt from the statute. The CAA applies to any pollutant source that meets its definition of “major”.

Most agricultural operations are not major sources of pollution, and few have been required to comply with the CAA’s requirements.  However, agricultural air pollution has become more of an issue as EPA implements NAAQS for particulates and as nonattainment areas looks for ways to reduce pollutants.  Emissions from animal feeding operations, such as ammonia, can transform into secondary particulate matter that could violate the NAAQS.  Other agriculture pollutants include dust stirred from operations, diesel emissions from farm equipment, and emissions from crop burning.  With pressure from advocacy groups, further regulations of these type of emissions may be forthcoming.  Complying with the provisions of the CAA and knowing the relevant law is important for any agriculture participant in order to avoid enforcement by the EPA.