Clean Air Act (CAA; US)
The purpose of the CAA is to protect public health and welfare by controlling ambient air pollution levels. In order to facilitate those goals the 1977 revisions to the CAA established the National Ambient Air Quality Standards (NAAQS; US Code, 7409; Clean Air Act Section 109; NAAQS). Under the NAAQS provisions, the EPA must establish emissions standards for six major criteria air pollutants that cause adverse health and environmental consequences: sulfur dioxide; lead; carbon monoxide; nitrogen dioxides; ozone; hydrocarbons; and particle matter (in two forms; PM less than 10 microns in size; and PM less than 2.5 microns in size). National primary and secondary NAAQS are established by law (see Air Criteria for these standards).
The CAA is organized around establishment of Air Quality Control Regions (AQRs). The Act charges the Governor of each state to establish AQRs. Each state assesses air quality in each region with respect to the NAAQS noted above, and must determine if each AQR falls into the following categories: (1) a non-attainment area, or an area that does not meet the primary or secondary NAAQS; an attainment are, or area that means the primary or secondary NAAQS standards; and (3) unclassifiable, areas for which available information cannot be used to determine if air quality complies with the primary or secondary NAAQS standards. States with areas that are defined as non-attainment must submit a plan (State Implementation Plan, SIP Plans) to the EPA describing plans to achieve facilitation of attainment. States may be sanctioned for failure to design appropriate plans or failure to meet attainment for AQRs ( Sanctions 1; Sanctions 2; and Sanctions 3). Specific rules for non-attainment area are also spelled out in Part D of the CAA, Plan Requirement for Nonattainment Areas. (For map of designated non-attainment counties see, MAP, accessed February 10, 2014).
Section 112 of the CAA addresses hazardous air pollutants. Hazardous air pollutants are listed in section (b). This section applies to major sources of pollution emitted within an area, and may not exceed 10 million tons of emissions per year for any hazardous air pollutant, or 25 million tons of emissions per year for any combination of hazardous air pollutants.
The CAA also includes New Source Performance Standards (NSPS; section 111) for new stationary pollution sources. This also includes modifications to existing stationary sources of pollution. Each state must submit a State Implementation plan designating standards for implementation of NSPS and the enforcement of those standards. NSPS are judged by Best Available Control Technology standards (BACT).
State standards under the CAA are also guided by provisions in Part C of the CAA, the Prevention of Significant Deterioration (PSD; CAA, Part C, sections 160-169B). These standards apply to NAAQS areas that meet attainment status, and are designed to prevent those areas from slipping into non-attainment status.