California Ambient Air Quality Standards (CAAQS)

This page reviewed November 24, 2009.

Air pollution harms the health of California citizens, damages agricultural crops, forests and other plants, and creates the haze that reduces visibility. A large body of scientific evidence associates air pollution exposure with a variety of harmful health effects. That's why the California Air Resources Board (ARB) and the U.S. Environmental Protection Agency (U.S. EPA) have adopted ambient (outdoor) air quality standards. These legal limits on outdoor air pollution are designed to protect the health and welfare of Californians. This site describes California's air quality standards, the air pollutants, and their harmful effects. For a complete listing of the pollutants and their associated standards check out our Ambient Air Quality Standards Chart. For more detailed information on specific pollutants with established California ambient air quality standards, click on the name of the pollutant in the list below.

Air Pollutants Having Ambient Air Quality Standards

Particulate Matter (PM10 and PM2.5)

Sulfur Dioxide (SO2)

Ozone (O3)

Visibility Reducing Particles

Nitrogen Dioxide (NO2)



Hydrogen Sulfide (H2S)

Carbon Monoxide (CO)

Vinyl Chloride

What is an ambient air quality standard?
Ambient air quality standards (AAQS) define clean air, and are established to protect even the most sensitive individuals in our communities. An air quality standard defines the maximum amount of a pollutant that can be present in outdoor air without harm to the public's health. California law authorizes the ARB to set ambient (outdoor) air pollution standards (California Health & Safety Code section 39606) in consideration of public health, safety and welfare. For a  brief history of standard setting, click here.

State and National Standards
The Federal Clean Air Act requires the U.S. Environmental Protection Agency to set outdoor air quality standards for the nation. It also permits states to adopt additional or more protective air quality standards if needed. California has set standards for certain pollutants, such as particulate matter and ozone, which are more protective of public health than respective federal standards. California has also set standards for some pollutants that are not addressed by federal standards.

Who is harmed by air pollution?
Studies have shown that the elderly and people with certain health conditions are more susceptible to the harmful effects of air pollution. Infants and children may also be more susceptible because they spend more time outdoors, are more active and have higher breathing rates. For more information, check out our Health and Air Pollution page.

How are ambient air quality standards set?
The Children's Environmental Health Protection Act (CEHPA, California Senate Bill 25, Escutia, 1999) required the ARB and Office of Environmental Health Hazard Assessment to evaluate all ambient air quality standards by December 2000 to determine whether these standards adequately protect human health, particularly that of infants and children. The CEHPA also required staff to prioritize those standards found to be inadequate for full review and possible revision. The evaluation found that health effects may occur in infants, children, and other potentially susceptible groups exposed to pollutants at levels near several of the current standards, with PM10, ground-level ozone (O3) and nitrogen dioxide (NO2) receiving the highest priority for review and possible revision.
In June of 2002, staff completed a review of published studies on the health effects of particulate matter and sulfates, the highest priority pollutant. The ARB adopted staff recommendations for revisions to the PM10 standard and established a new PM2.5 annual standard. For more information regarding the PM and Sulfates Standards Review, please follow the link to the PM Standards Review. Staff also reviewed the published scientific literature on ground-level ozone and nitrogen dioxide and subsequently recommended revisions to standards for these two pollutants. The revised standards for ozone and nitrogen dioxide went into effect on May 17, 2006 and March 20, 2008, respectively. Please follow these links for more information about the Ozone Standard Review and the Nitrogen Dioxide Standards Review
Over time, the lower priority ambient air quality standards will be reviewed as well. Regulations also require the review of standards whenever substantial new information pertaining to ambient air quality standards becomes available, and at least once every five years.

Attainment of Air Quality Standards
View state and federal designation maps indicating which geographical areas do or do not meet air quality standards.

For more information on Ambient Air Quality Standards please contact
Dr. Linda Smith at (916) 327-8225.