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Particulate Matter

Particulate matter (PM) is a complex mixture of tiny particles that consists of dry solid fragments, solid cores with liquid coatings, and small droplets of liquid. These 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. Particles 10 microns or less in diameter are defined as "respirable particulate matter" or "PM 10". Fine particles are 2.5 microns or less in diameter (PM 2.5) and can contribute to a reduction of visibility. Some research has linked exposure to outdoor PM 10 and PM 2.5 levels with increased risk of hospitalization for lung and heart-related respiratory illness, including emergency room visits for asthma. PM exposure has also been linked in certain studies to be associated with increased risk of premature deaths, especially in the elderly and people with pre-existing cardiopulmonary disease. In children, other studies have shown potential associations between PM exposure and reduced lung function and increased respiratory symptoms and illnesses. Other research has not found the effects mentioned above.

PM reduces visibility as light is scattered by the particles in the atmosphere and forms a whitish haze. The acidic portion of PM (nitrates, sulfates) can harm crops, forests, aquatic and other ecosystems.

What Can I Do?

Particulate matter can come from uncontrolled combustion, such as from fireplaces, outdoor grills and nearby roadways. Particulate matter is also present inside the home, from visible household dust to materials suspended in the air that are released from fabrics and building materials. A clean house and careful selection of natural materials used in the home are known to be helpful in making breathing easier.

Air Quality is Clean and Getting Significantly Cleaner Even as Our Economy Grows

Between 1970 and 2004, U.S. gross domestic product increased 187 percent, vehicle miles traveled increased 171 percent, energy consumption increased 47 percent, and U.S. population grew by 40 percent. During the same time period, total emissions of the six principal air pollutants dropped by 54 percent.

Diesel trucks and buses will soon be 95% cleaner than today’s models for smog-causing emissions and 90 percent cleaner for particulate matter.

Existing Standard Protects Public Health

EPA’s analysis shows that the 1997 PM 2.5 standard is MORE PROTECTIVE than EPA had assumed when it first issued the 1997 standard.

EPA’s 2006 risk assessment estimates generally lower risk upon attainment of the 1997 PM 2.5 NAAQS than EPA estimated when it set those standards in 1997.