Control of Air Pollution From Motor Vehicle Transportation by the Federal and State Governments
Since 1967 the Clean Air Act (CAA) has had a program to control the common air pollutants that are emitted in large quantities in order to achieve the prescribed ambient air quality standards.1 Since 1970 this CAA program has been based on uniform national ambient air quality standards (NAAQS)2 first promulgated by the Administrator of the newly created Environment Protection Agency (EPA)3 on April 30, 1971.4 The NAAQS are numerical values for the concentration of criteria pollutants in the ambient air. These “criteria” pollutants have not changed much in thirty years. There were six original criteria pollutants: particulates, sulfur dioxide (SO2), carbon monoxide (CO), ozone, nitrogen dioxide (NO2), and hydrocarbons (HC).5 In 1978 the EPA added lead as a criteria pollutant,6 and in 1983 the Agency delisted hydrocarbons.7 In 1987, the EPA changed the particulate standard to only control particles less than or equal to ten micrometers in diameter (PM10).8 While hydrocarbons were removed as criteria pollutants, chemically reactive hydrocarbons known as non-methane hydrocarbons (NMHCs) and volatile organic compounds (VOCs) continued to be regulated by the CAA because they are chemical precursors to the formation of tropospheric ozone, which is a criteria pollutant; nitrogen oxides also are regulated because they are precursors to ozone formation.9
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