AIR QUALITY INFORMATION
National Ambient Air Quality Standards
The Clean Air Act, which was last amended in 1990, requires EPA to set National Ambient Air Quality Standards (NAAQS) for wide-spread pollutants from numerous and diverse sources considered harmful to public health and the environment. The Clean Air Act established two types of national air quality standards. Primary standards set limits to protect public health, including the health of "sensitive" populations such as asthmatics, children, and the elderly. Secondary standards set limits to protect public welfare, including protection against visibility impairment, damage to animals, crops, vegetation, and buildings. The Clean Air Act requires periodic review of the science upon which the standards are based and the standards themselves.
EPA has set NAAQS for six principal pollutants, which are called "criteria" pollutants:
*To learn more about each of these pollutants click on the link.
Below is a summary table of the current NAAQS:
|Carbon Monoxide||9 ppm (10 mg/m3)||8-hour1||None|
|Lead||1.5 µg/m3||Quarterly Average||Same as Primary|
|Nitrogen Dioxide||0.053 ppm
|Annual (Arithmetic Mean)||Same as Primary|
|Particulate Matter (PM10)||50 µg/m3
||Annual2 (Arith. Mean)
||Same as Primary|
|Particulate Matter (PM2.5)||15 µg/m3
||Annual3 (Arith. Mean)
||Same as Primary|
|Ozone||0.08 ppm||8-hour5||Same as Primary|
|0.12 ppm||1-hour6||Same as Primary|
|Sulfur Oxides||0.03 ppm||Annual (Arith. Mean)|
6 (a) The standard is attained when the expected number of days per calendar year with maximum hourly average concentrations above 0.12 ppm is <= 1, as determined by appendix H. (b) The 1-hour standard is applicable to all areas notwithstanding the promulgation of 8-hour ozone standards under Sec. 50.10. On June 2, 2003, (68 FR 32802) EPA proposed several options for when the 1-hour standard would no longer apply to an area.