California Air Resources Board

What Are Criteria Pollutants?

Criteria pollutants are six common air 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.

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 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 a toxic metal found in older products and some 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

Reactive Organic Gases (ROGs)

Reactive organic gases evaporate into the air and react with other air pollutants. These gases are precursors to the formation of ground-level ozone.

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

Major sources include motor vehicles, industrial processes, and some consumer products (e.g.paints, cleaning products)