U.S. EPA and Iowa DNR regulate 187 air pollutants known or suspected to cause cancer or other serious health effects such as reproductive effects or birth defects, or adverse environmental consequences. These pollutants are called hazardous air pollutants (HAP) or air toxics.
Air toxics are generally more localized than the criteria pollutants and the highest levels are close to their sources. Most air toxics originate from man-made sources, including cars and trucks, factories, power plants and refineries, as well as some building materials and cleaning solvents.
U.S. EPA is responsible for setting national standards for regulating sources of HAP, called National Emission Standards for Hazardous Air Pollutants (NESHAP).
Because of the difficulty in assessing air toxic health risks with the original Clean Air Act enacted in 1970, Congress amended the Clean Air Act in 1990 to emphasize controlling emissions of air toxics through available control technology, and then periodically evaluating any remaining risk from air toxics.