The 1970 amendments to the Clean Air Act required the Environmental Protection
Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for certain
pollutants known to be hazardous to human health. The EPA has identified and
set standards to protect human health and welfare for six pollutants: ozone,
carbon monoxide, total suspended particulates, sulfur dioxide, lead, and
nitrogen oxide. The term "criteria pollutants" derives from the
requirement that the EPA must describe the characteristics and potential health
and welfare effects of these pollutants. It is on the basis of these criteria
that standards are set or revised.