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Criteria Pollutants    At a Glance    In Depth

Nitrogen Dioxide


Carbon Monoxide

Sulfur Dioxide

Particulate Matter



Major Air Pollutants: What Are They? Where Do They Come From?

Air pollution is any visible or invisible particle or gas found in the air that we breathe that harms our health and welfare.

The Criteria Pollutants

For several decades, scientists have studied the harmful affects of common air pollutants, alone or in combination, on human health and the health of the environment. This ongoing scientific research has established unsafe exposure levels for certain pollutants. In response, the U.S. Environmental Protection Agency has set and regulates levels of exposure to specific pollutants according to clear scientific guidelines. These national ambient or outdoor air quality standards prescribe a level for each criteria pollutant that cannot be exceeded during a certain time period. At this time, the U.S. EPA regulates 6 pollutants: ozone, particulate matter, carbon monoxide, nitrogen dioxide, sulfur dioxide, and lead. California has set even more stringent standards for some of these pollutants and has established standards for sulfate particles, hydrogen sulfide, vinyl chloride and visibility reducing particles as well.

Criteria Pollutants at a Glance
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