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Reviewing National Ambient Air Quality Standards – Scientific and Technical Information

The Clean Air Act, which was last amended in 1990, requires EPA to set National Ambient Air Quality Standards (NAAQS) for pollutants that are common in outdoor air, considered harmful to public health and the environment, and that come from numerous and diverse sources. The Clean Air Act established two types of national air quality standards. Primary standards set limits to protect public health, including the health of at-risk populations such as people with pre-existing heart or lung disease (such as asthmatics), children, and older adults. 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. For more information on EPA's process for reviewing the NAAQS, see NAAQS Review Process.

EPA has set NAAQS for six principal pollutants, which are called "criteria" pollutants. They are listed below. For a summary table of the current NAAQS, see the NAAQS Table.

For further information about the current or prior review of any of the NAAQS, please use the links listed below:

Ozone (O3) Air Quality Standards   Particulate Matter (PM) Air Quality Standards
     
Carbon Monoxide (CO) Air Quality Standards   Lead (Pb) Air Quality Standards
     
Sulfur Dioxide (SO2) Primary Air Quality Standards
Sulfur Dioxide (SO2) Secondary Air Quality Standards
  Nitrogen Dioxide (NO2) Primary Air Quality Standards
Nitrogen Dioxide (NO2) Secondary Air Quality Standards

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