The 1970 Clean Air Act (CAA), significantly amended in 1977 and again in 1990, regulates air pollution emissions from "stationary" sources (e.g., factories, smokestacks, etc.), mobile sources (e.g., motor vehicles), and certain "indirect" sources (e.g., highways, malls, parking lots, etc., that attract mobile sources to the location). Specified "criteria" pollutants such as sulfur dioxide, nitrogen oxide, carbon monoxide, particulates (i.e., soot, fly ash, etc.), and lead are directly regulated, as are "hazardous" air pollutants that the EPA determines are likely to cause death or serious physical injuries. Congress listed some 189 hazardous air pollutants in its 1990 amendments to the original law. Many of these hazardous air pollutants are fairly common chemicals, such as benzene, dry-cleaning solvents, and others that pose scientifically verifiable health dangers. Although it has long been a criteria pollutant, lead is now known to be especially dangerous to human health. The 1990 amendments require further reductions in the criteria oxides that cause smog and acid rain.
Permitted sources have monitoring and reporting requirements. Permitting decisions are based, in part, on whether the location of a stationary source emitting a particular pollutant is in an "attainment area" for that pollutant (i.e., the local pollution generated by that pollutant does not exceed the specified threshold). Conversely, the area may be regarded as "nonattain-ment" in terms of that pollutant and the applicable standard (i.e., the threshold is exceeded), in which case allowable emissions will be severely curtailed. Mobile source emissions are regulated in the main by the EPA's establishment of specific emission standards for several classifications of vehicles; these are imposed on manufacturers. The 1990 amendments planned the development of "clean fuel" vehicles using hybrid or low polluting fuels and, especially for notoriously dirty urban buses, clean fuel fleets. Vehicle fuel is also regulated in regard to its constituents, with limitations imposed on gasoline sold in ozone or carbon monoxide nonattainment areas. After 1995, leaded gasoline was absolutely barred from commerce.
States exercise responsibility primarily by the formulation of State Implementation Plans (SIPs), which are subject to EPA approval. If a SIP is unavailable or ineffectively carried out by the state, the EPA enforces the act. Citizen suits are also permitted, whereby private citizens, subject to notice requirements, have the authority to act as private attorney generals in seeking judicial enforcement. They may not, however, recover damages. see also Air Pollution; Dry Cleaning; Electric Power; Laws and Regulations, United States; Toxic Release Inventory; Vehicular Pollution.
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