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California Air Resources Board

Particulate Matter Air Pollution in California
Airborne particles 10 microns in diameter and smaller, called PM10, impact our health and our environment.  Graphs that characterize PM10 air quality across California can be accessed from the graph icons to the left of this page.  PM10 particles can be directly emitted to the atmosphere from a wide variety of  sources.  They can also be formed in the atmosphere when gaseous pollutants such as sulfur dioxide and nitrogen dioxide undergo a chemical reaction in the atmosphere.  When inhaled, PM10 particles can travel to deep parts of the lungs and remain there causing respiratory illness, lung damage, and premature death in sensitive individuals.  PM10 also reduces visibility.

The U.S. EPA and the ARB have established annual and daily
air quality standards for PM10 that identify acceptable levels of PM10 in the ambient air.  Annual PM10 standards, i.e., the State annual geometric mean standard of 30 micrograms per cubic meter and the federal annual arithmetic mean standard of 50 micrograms per cubic meter, were established to protect the public and the environment from the effects of long-term exposure to ambient PM10 concentrations.  During the last 9 years, annual geometric mean PM10 concentrations in areas of California have reached as high as 133.7 micrograms per cubic meter, more than four times the State annual standard.  In 1988, annual PM10 concentrations exceeded the State standard in eleven of the State's fifteen air basins.  In 1996, despite measures to control PM10 emissions, annual PM10 concentrations still exceeded the standard in five air basins.

The 24-hour PM10 standards, i.e., the State standard of 50 micrograms per cubic meter and the federal standard of 150 micrograms per cubic meter, were established to protect the public from health effects of short-term exposures.  Although the overall air quality in California has been improving over the last 9 years, for the same time period the maximum 24-hour PM10 concentrations exceeded the 24-hour State standard in at least thirteen air basins each year.   The trend of 24-hour PM10 exceedances for each air basin during 1988 through 1996 is shown in a graph.

At many California air basins, ambient PM10 concentrations exceeded the State 24-hour PM10 standard by large margins.  Ten of the fifteen air basins have the maximum 24-hour concentrations of over 100 micrograms per cubic meter, or more than two times the 24-hour standard.  The maximum 24-hour PM10 concentrations measured in each air basin during 1994 through 1996 are shown in a  graph.

At many monitoring sites in California, the 24-hour State standard was exceeded on numerous days on which measurements were taken.  At the fifteen worst PM10 sites in California, the average percent of samples exceeding the air quality standard for PM10 during 1994 through 1996 ranged from 40 to 78 percent.

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This page last revised on October 9, 1997
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