Clean Air Act: An Overview

Background and Statutory Framework

The Clean Air Act (“CAA”) was originally enacted in 1955 and was amended in 1990 as an effort to protect the nation’s air quality. 42 U.S.C. 7401–7671q. The purpose of the CAA is “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 Act provides a comprehensive and complex regulatory framework for regulating stationary and mobile 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. 42 U.S.C. § 7409.  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.


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.


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.