National Ambient Air Quality Standards (NAAQS)

The Clean Air Act, which was last amended in 1990, requires EPA to set National Ambient Air Quality Standards for pollutants 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 decreased visibility, damage to animals, crops, vegetation, and buildings.

The EPA Office of Air Quality Planning and Standards (OAQPS) has set National Ambient Air Quality Standards for six principal pollutants, which are called "criteria" pollutants. They are listed below. Units of measure for the standards are parts per million (ppm) by volume, parts per billion (ppb) by volumemilligrams per cubic meter of air (mg/m3), and micrograms per cubic meter of air (ug/m3). 

National Ambient Air Quality Standards (9/27/17)
Pollutant Standard Value Standard Type
Carbon Monoxide    
8-Hour Average 9 ppm  Primary
1-Hour Average 35 ppm  Primary
Nitrogen Dioxide (NO2)    
1-Hour Average 100 ppb Primary 
1-Year Average 53 ppb Primary & Secondary
Ozone (O3)    
8-Hour Average 0.070 ppm Primary & Secondary
Lead (Pb)    
Rolling Three Month Average  0.15 µg/m3 Primary & Secondary
Fine Particulate (PM2.5)    
1-Year Average 12 µg/m3 Primary 
1-Year Average 15 µg/m3 Secondary
24-Hour Average 35 µg/m3 Primary & Secondary
Particulate (PM10)    
24-Hour Average 150 µg/m3 Primary & Secondary
Sulfur Dioxide (SO2)    
1-Hour Average 75 ppb   Primary
3-Hour Average 0.50 ppm  Secondary