An air pollutant is any substance in the air that can cause harm to humans or the environment. Pollutants may be natural or man-made and may take the form of solid particles, liquid droplets or gases.
The 1990 Clean Air Act Amendments lists 188 toxic air pollutants that EPA is required to control. These pollutants are divided into various groups, including particulate matter, volatile organic comp
ounds (VOCs) and halogen compounds. Also included are more commonly-known pollutants such as lead, mercury and asbestos.
Recommended EPA Web pages