The Clean Air Act (CAA) of 1970 identified six common air pollutants of concern, called criteria pollutants. The criteria pollutants are carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter, and sulfur dioxide. Criteria pollutants are the only air pollutants with national air quality standards that define allowable concentrations of these substances in ambient air.
Exposure to these substances can cause health effects, environmental effects, and property damage. Health effects include heart or lung disease, respiratory damage, or premature death. Environmental effects include smog, acid rain, radiation, and ozone depletion.
EPA reports that releases of all criteria air pollutants except nitrogen oxides have been in decline since the passage of the 1970 CAA. Overall air quality has improved significantly nationwide since the 1980s. These improvements, however, have not eliminated air quality problems, and major efforts to control pollution sources are still required to ensure everyone breathes air that meets CAA standards.
The links below provide information on the health impacts of exposure to each criteria pollutant.
Carbon monoxide (CO) is a colorless, odorless, and poisonous gas and one of six criteria pollutants for which EPA has established protective standards.Learn more.
Lead is a metal found naturally in the environment as well as in manufactured products. It is one of six criteria pollutants for which EPA has established protective standards. Learn more.
Ozone is a gas that forms in the atmosphere when three atoms of oxygen are combined. It is not emitted directly into the air but is created at ground level by a chemical reaction between oxides of nitrogen, and volatile organic compounds in the presence of sunlight. Learn more.
Nitrogen dioxide is a brownish, highly reactive gas present in all urban atmospheres. Nitrogen dioxide is a criteria pollutant that can irritate the lungs, cause bronchitis and pneumonia, and lower resistance to respiratory infections. Learn more.
Particulate matter, or PM, is the term for small particles found in the air including dust, dirt, soot, smoke, and liquid droplets. Particles can be suspended in the air for long periods of time. Learn more.
Sulfur dioxide is a colorless, reactive gas produced during burning of sulfur-containing fuels such as coal and oil, during metal smelting, and by other industrial processes.Learn more.