In 1990, Congress amended the Clean Air Act to provide for more stringent regulation of air pollution. The 1990 Clean Air Act Amendments (CAAA) impose increased limitations on emissions of criteria pollutants carbon monoxide (CO), nitrogen oxides (NO_X), sulfur dioxide (SO_2), particulate matter (PM), volatile organic compounds (VOC), and lead as well as 189 listed hazardous air pollutants (HAPs). The 1990 CAAA require industry to reduce and track emissions to a higher degree than ever before.
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