The 1990 Clean Air Act Amendments (CAA) required the EPA to take specific actions to reduce emissions and risks from air toxics. Air toxics (also known as hazardous air pollutants or HAPs) are pollutants known to cause or suspected of causing cancer as well as respiratory, neurological, reproductive and other serious health effects. Air toxics are emitted by mobile sources (e.g., cars, trucks and construction equipment); large or major sources (e.g., factories and power plants); smaller, or area, sources (e.g., gas stations and dry cleaners); and background sources (e.g., longrange transport of pollution and natural emissions sources such as wildfires). Examples of air toxics include benzene, found in gasoline; perchloroethylene, emitted from some dry cleaning facilities; and methylene chloride, used as a solvent by several industries. Congress expressed under CAA section 112(k) that emissions of air toxics, individually or in the aggregate, may present significant risks to public health in urban areas and directed the U.S. Environmental Protection Agency (EPA) to develop a strategy to reduce these risks. Considering the large number of persons exposed and the risks of carcinogenic and other adverse health impacts from HAPs, the EPA believed that to reduce public health risks in urban areas, aggregated exposures from all sources had to be addressed. Therefore, it developed the Integrated Urban Air Toxics Strategy in 1999, using all available authorities, for reducing cumulative public health risks in urban areas posed by the aggregated exposures from all sources, including major stationary sources, smaller area stationary sources and mobile sources. The EPA also recognized that national regulations alone would not be enough to address all of the issues, particularly those affecting urban areas.