Hazardous air pollutants that are known or suspected to cause cancer or other serious health effects (such as birth or developmental defects). The U. S. Clean Air Act Amendments of 1990 require emission reductions for 188 hazardous air pollutants from industrial factories and other sources. As of 1996, the U. S. Environmental Protection Agency has issued standards for 47 source categories, such as chemical plants, oil refineries, aerospace manufacturers, and steel mills, as well as dry cleaners, commercial sterilizers, secondary lead smelters, and chromium electroplating processors. Compare designated pollutant, criteria pollutants; see downwash.