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Ambient Air Quality Standards (AAQS) for Particulate Matter

What is particulate matter (PM)? Revision of the PM Standards
Why is the ARB is concerned about PM? What are the major harmful health effects
associated with PM exposure?
What are the ambient air quality standards forPM?

Particulate matter (PM) is a complex mixture consisting of varying combinations of dry solid fragments, solid cores with liquid coatings and small droplets of liquid. These tiny particles vary greatly in shape, size and chemical composition, and can be made up of many different materials such as metals, soot, soil and dust. PM may also contain sulfate particles. California has a separate ambient air quality standard for sulfates.
PM may be divided into many size fractions, measured in microns (a micron is one-millionth of a meter). ARB regulates two size classes of particles – particles up to 10 microns (PM10) and particles up to 2.5 microns in size (PM2.5). PM2.5 particles are a subset of PM10.
PM10 and PM2.5 are each measured and expressed as the amount (in micrograms) of particles
contained in a cubic meter of air, expressed as micrograms per cubic meter (µg/m
What are the Sources of
Airborne Particulate Matter?

Burning fuels, such as gasoline, oil, diesel or
wood, produce most of the PM2.5 pollution found
in outdoor air, and much of the PM10. Wind-blown
dust also contributes to PM10 pollution.

Why is the ARB concerned about particulate matter?
The ARB is concerned about Californians’ exposures to PM2.5- and PM10-sized particles because of the potential harmful health effects that can result.
PM 2.5 and PM10 particles easily penetrate into the airways and lungs where they may produce harmful health effects such as the worsening of heart and lung diseases. The risk of these health effects is greatest in the elderly and the very young. Exposure to elevated concentrations of PM is also associated with increased hospital and doctor visits and increased numbers of premature deaths.
What are the PM Standards?
The State of California has established ambient air quality standards for PM. These standards define the maximum amount of particles that can be present in outdoor air without threatening the public’s health. In June of 2002, the California ARB adopted new, revised PM standards for outdoor air, lowering the annual PM10 standard from 30 µg/m3 to 20 µg/m3 and establishing a new annual standard for PM2.5 of 12 µg/m3.
California’s ambient air quality standards for PM are designed to protect the most sensitive groups of people, including infants and children, the elderly and persons with heart or lung disease.

For more information, see the Ambient Air Quality Standards chart at

State and Federal Ambient Air Quality Standards for Particulate Matter
California ARB Standard PM10 Federal EPA Standard PM10
Annual Average 20 µg/m3 N/A
24-Hour Average 50 µg/m3 150 µg/m3
California ARB Standard PM2.5 Federal EPA Standard PM2.5
Annual Average 12 µg/m3 15.0 µg/m3
24-Hour Average ——– 35 µg/m3
California’s PM standards are more protective of human health than the corresponding set by EPA. See the EPA site for the new federal PM10 and PM2.5 ambient air quality standards at
Revision of the PM Standards
The ARB adopted new PM standards in June of 2002, responding to requirements of the Children’s Environmental Health Protection Act (Senate Bill 25, Escutia 1999). This Act requires the evaluation of all health-based ambient air quality standards to determine if the standards adequately protect human health, particularly that of infants and children. The subsequent review of the PM standards resulted in the recommendation of more health-protective ambient air quality standards for PM10 and a new standard for PM2.5. More details of this review are available in the staff report, “Public Hearing to Consider Amendments to the Ambient Air Quality Standards for Particulate Matter and Sulfates.” The new PM standards became effective in 2003.

Information about how the ARB sets ambient air quality standards can be found at

What kinds of harmful effects can PM cause?
Concentrations of PM above the current standards may result in harmful health effects. Since the small particles that make up PM can easily penetrate deep into the lungs, scientists have studied the effects of this type of pollution on human health. Both short- and long-term exposures to PM have been shown to lead to harmful health effects. A large body of evidence has shown significant associations between measured levels of PM outdoors and daily increases in the numbers of human deaths. In addition, scientists have observed higher rates of hospitalizations, emergency room visits and doctor’s visits for respiratory illnesses or heart disease during times of high PM concentrations. During these periods of high PM levels, scientists also observed the worsening of both asthma symptoms and acute and chronic bronchitis. Scientists have found a relationship between high PM levels and reductions in various aspects of the healthy functioning of people’s lungs.
Which groups are most susceptible to health effects from PM?

  • ·        The Elderly
  • ·        People with Heart and / or Lung Disease
  • ·        Children and Infants
The elderly and people with heart and/or lung diseases are particularly at risk to the harmful effects from PM exposure. A data analysis from ARB’s Children’s Health Study shows health effects in children, as well. This study showed that in communities highly polluted with PM, children’s lungs developed more slowly and did not move air as efficiently as children’s lungs in clean air communities. Children and infants are susceptible to harm from inhaling pollutants such as PM because they inhale more air per pound of body weight than do adults – they breathe faster, spend more time outdoors and have smaller body sizes. In addition, children’s immature immune systems may cause them to be more susceptible to PM than healthy adults. Further research may clarify the relationship between PM exposure and children’s health.
PM levels in most areas of California exceed current state PM standards from a few to many times each year. ARB is working diligently to reduce levels of PM and other kinds of air pollution in California’s outdoor air. You can also help in the fight against air pollution – click here for further information

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

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