National Ambient Air Quality Standards (NAAQS)

The Environmental Protection Agency establishes national ambient air quality standards for six principal pollutants: carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter, and sulfur dioxide. These standards set maximum allowable concentrations in outdoor air to protect public health with an adequate margin of safety.

Primary standards are designed to protect public health, including the health of sensitive populations such as asthmatics, children, and the elderly. Secondary standards protect public welfare, including protection against decreased visibility, damage to animals, crops, vegetation, and buildings.