National Ambient Air Quality Standards

The National Ambient Air Quality Standards (NAAQS) are standards established by the United States Environmental Protection Agency that apply for outdoor air throughout the country. Primary standards are designed to protect human health, including sensitive populations such as children, the elderly, and individuals suffering from respiratory disease. Secondary standards are designed to protect public welfare (e.g. building facades, visibility, crops, and domestic animals).

NAAQS requires the EPA to set standards on six criteria air contaminants:


 * 1) Ozone (O3)
 * 2) Particulate Matter
 * 3) * PM10, coarse particles: 2.5 micrometers (μm) to 10 μm in size (although current implementation includes all particles 10 μg or less in the standard)
 * 4) * PM2.5, fine particles: 2.5 μm in size or less
 * 5) Carbon monoxide (CO)
 * 6) Sulfur dioxide (SO2)
 * 7) Nitrogen oxides (NOx)
 * 8) Lead (Pb)

Standards
Each standard has its own criteria for how many times it may be exceeded, in some cases using a three year average.

As of June 15, 2005, the 1-hour ozone standard no longer applies to areas designated with respect to the 8-hour ozone standard (which includes most of the United States, except for portions of 10 states).

Source: USEPA