EPA Terminology Glossary

Air pollutant is any substance in air that could, in high enough concentrations, harm plants, animals, people, or material. Pollutants may include almost any natural or artificial composition of airborne matter.

Best Available Control Technology (BACT) is a pollution control standard based on the maximum degree of emission reduction (considering energy, environmental, and economic impacts) achievable through application of production processes and available methods, systems, and techniques. BACT is required under EPA’s new source review program and is implemented on a case-by-case basis for major new or modified emissions sources in “attainment areas” (areas that are meeting the applicable National Ambient Air Quality Standard) and applies to each regulated pollutant.

Clean Air Act is a set of laws that defines EPA’s responsibilities for protecting and improving the national air quality and stratospheric ozone layer. The Clean Air Act focuses on: reducing outdoor concentrations of air pollutants that cause smog, haze, acid rain, and other problems; reducing emissions of air pollutants; and phasing out the use of chemicals that destroy stratospheric ozone.

Criteria Pollutants are certain pollutants known to be harmful to human health and welfare and for which National Ambient Air Quality Standards are established. EPA has identified and set standards to protect human health and welfare for ozone, carbon monoxide, particulate matter, sulfur dioxide, lead, and nitrogen oxide.

Federal Implementation Plan (FIP) is a federally implemented plan to achieve attainment of air quality standards and is used when a state is unable to develop an adequate plan.

Hazardous Air Pollutants, also known as toxic air pollutants or air toxics, are air pollutants not covered by ambient air quality standards but which as defined in the Clean Air Act, may present a threat of adverse human health effects, such as cancer or birth defects, or adverse environmental and ecological effects. Such pollutants include asbestos, beryllium, mercury, benzene, coke oven emissions, radionuclides, and vinyl chloride.

Maximum Available Control Technology (MACT) is a pollution control standard for sources of air pollution requiring the maximum reduction of hazardous emissions, taking cost and feasibility into account. Under the Clean Air Act Amendments of 1990, the MACT must not be less than the average emission level achieved by controls on the best performing 12 percent of existing sources, by category of industrial and utility sources.

National Ambient Air Quality Standards (NAAQS) are standards established at the national level by EPA under the Clean Air Act that apply to outdoor air throughout the country. The Clean Air Act establishes two types of air quality standards. Primary standards set limits to protecting public health while secondary standards set limits to protect public welfare.

New Source Performance Standards (NSPS) are uniform national EPA air emission standards, which limit the amount of pollution allowed from new sources or from modified existing sources.

New Source Review (NSR) is a Clean Air Act requirement that stipulates State Implementation Plans must include a permit review that applies to the construction and operation of new and modified stationary sources to ensure attainment of national ambient air quality standards.

Operating Permits are legally enforceable documents issued mostly by state and local permitting authorities to individual air pollution sources, which include enforceable standards applicable to those sources. Under title V of the Clean Air Act, all large sources and a limited number of smaller sources of air pollution are required to obtain operating permits that assure compliance with all provisions of the Act.

Prevention of Significant Deterioration (PSD) is an EPA program in which state and/or federal permits are required in order to restrict emissions from major sources or major modifications in places where air quality already meets or exceeds primary and secondary ambient air quality standards.

State Implementation Plans (SIP) is a state plan for the establishment, regulation, and enforcement of air pollutant standards established and approved by EPA.