California Air Resources Board

What are criteria pollutants?

Criteria pollutants are pollutants that the U.S. Environmental Protection Agency (EPA) regulates under the Clean Air Act. 

The California Air Resources Board (CARB) works to monitor, control, and reduce these pollutants throughout the state.

For more information on the standards the EPA sets for criteria pollutants click here.

List of the six criteria pollutants

Particulate Matter (PM)

Particulate matter (PM) are tiny particles suspended in the air that vary in size, composition, and origin.

Human health effects include respiratory issues, heart problems, and decreased lung function.

Major sources include construction sites, unpaved roads, fires, vehicle exhaust. Total PM refers to all particulate matter in the air. PM10 includes particles with a diameter up to 10 micrometers. PM2.5 includes particles with a diameter up to 2.5 micrometers.

Carbon Monoxide (CO)

Carbon monoxide is a colorless, odorless gas produced by incomplete combustion of carbon-containing fuels.

Human health effects include reduced oxygen delivery to organs and tissues.

Major sources include vehicle exhaust, industrial processes, and residential wood burning.

Sulfur Oxides (SOx)

Sulfur oxides are gases produced primarily from fossil fuel combustion at power plants and industrial facilities.

Human health effects include respiratory effects and increased asthma symptoms.

Major sources include fuel combustion, industrial processes, and shipping.

Lead (Pb)

Lead is also considered a toxic pollutant. Lead can be found in older consumer products and industrial processes.

Human health effects include neurological disorders, particularly in children.

Major sources include metal processing, aviation fuel, and waste incineration.

Nitrogen Oxides (NOx)

Nitrogen oxides are highly reactive gases formed from emissions from various combustion sources.

Nitrogen oxides are precursors to the formation of ground-level ozone.

Human health effects include respiratory inflammation and aggravated respiratory issues. Major sources include motor vehicles, power plants, and industrial boilers.

Ozone (O₃)

Ground-level ozone is a highly reactive gas that is not emitted directly into the air, but is formed when nitrogen oxides and volatile organic compounds (VOCs) react in the presence of sunlight.

Because ozone is a secondary pollutant, CARB focuses on monitoring and reducing its precursor emissions (i.e. volatile organic compounds and nitrogen oxides) rather than tracking ozone sources directly.

Human health effects include aggravated respiratory issues, throat irritation, and reduced lung function.

Major sources (of precursor emissions) include motor vehicles, industrial processes, and consumer products such as paints and cleaning products