Particulate matter pollution consists of very small solid and liquid particles suspended in the air. The "large" particles are often referred to as PM10 because they are about 10 microns in diameter. For comparison, a human hair is 70 microns in diameter. Finer particles, known as PM 2.5, are less than 2.5 microns in diameter and are as small as a grain of flour. Like carbon monoxide, particulate matter pollution is more problematic during winter when the temperature inversion traps the pollutants close to the ground. Particulate matter is one of the fundamental pollutants that form the Valley's familiar "brown cloud." Sources of particulate matter include air pollution from cars, trucks, buses, nonroad vehicles and equipment, unpaved roads, fireplaces, farming, power plants, and other industries.

Sources of Particulate Matter - Maricopa County, 1995

• Nonroad mobile sources include: gas powered lawn and garden equipment, generators, and construction and agricultural equipment.



• Area sources include: fuel burning equipment and woodburning.



• Onroad mobile sources include: gasoline and diesel trucks and cars.



• Biogenic sources include: plants and trees.



• Point sources include: manufacturers and power plants.

Current Situation

PM continues to be a problem in the Valley, which has until Dec. 31, 2006, to meet the federal standard for PM10. Several programs are in place to reach attainment by this deadline. For more information, read about Maricopa County's fugitive dust control program and agricultural best management practices.

What are the Strategies in Place to Reduce PM?

• Dust control plans are required for construction projects in Maricopa County.



• Best management practices are required for commercial farms.



• Unpaved roads/parking lots are paved or otherwise stabilized.



• Vacant lots are stabilized.



• PM10 efficient sweepers are used.



• Maricopa County's clean burning fireplace ordinance.



• Maricopa County's no-burn day ordinance.



• Maricopa County's trip reduction program.



• The Clean Air Program is a public education and marketing campaign that encourages the use of alternative forms of transportation and other pollution reducing strategies.

There are many ways for the public to help prevent a particulate matter exceedance. Find out how you can help to reduce pollution in the Valley.

Particulate matter pollution can be harmful to the public. Please visit health effects of particulate matter to learn more about the health risks of exposure to particulate matter pollution.