Information about Particulate (PM10)

Current conditions

Condensed from Measuring Air Quality: The Pollutant Standards Index; Office of Air Quality Planning and Standards, US EPA; EPA 451/K-94-001; February 1994.


Particulate matter (PM) is solid matter or liquid droplets from smoke, dust, fly ash, or condensing vapors that can be suspended in the air for long periods of time. It represents a broad class of chemically diverse particles that range in size from molecular clusters of 0.005 micrometers (µm) to coarse particles of 50-100 µm in diameter (100 µm is about the thickness of an average human hair). PM results from all types of combustion. The carbon-based particles that result from incomplete burning of diesel fuel in buses, trucks and cars are of particular concern. Another important combustion source is the burning of wood in stoves and fireplaces in residential settings. Also of concern are the sulfate and nitrate particles that are formed as a byproduct of SO2 and NO2 emissions, primarily from fossil fuel-burning power plants and vehicular exhausts.

The U.S. national ambient air quality standard was originally based on particles up to 25-45 µm in size, termed "total suspended particles" (TSP). In 1987, EPA replaced TSP with an indicator that includes only those paraticles smaller than 10 µm, termed PM10. These smaller particles cause most of the adverse health effects because of their ability to penetrate deeply into the lungs.

Health Effects

The observed human health effects of PM include breathing and respiratory symptoms, aggravation of existing respiraory and cardiovascular disease, alterations in the body's defense system against inhaled materials and organisms, and damage to lung tissue. Groups that appear to be most sensitive to the effects of PM include individuals with chronic lung or cardiovascular disease, individuals with influenza, asthmatics, elderly people, and children.

Marked increases in daily mortality have been statistically associated with very high 24-hour concentrations of PM10, with some increased risk of mortality at lower concentrations. Small increases in mortality appear to exist at even lower levels. Risks to sensitive individuals increase with consecutive, multiday exposures to elevated PM concentrations. The research also indicates that aggravation of bronchitis occurs with elevated 24-hour PM10 levels, and small decreases in lung function take place when children are exposed to lower 24-hour peak PM10 levels. Lung function impairment persists for 2-3 weeks following exposure to PM.

Air quality levels

The air quality standard for PM10, which is designed to protect public health with an adequate margin of safety, is 150 micrograms per cubic meter (µg/m3), averaged over 24 hours. EPA is required to issue a public alert when PM10 levels reach 350 µg/m3 on a 24 hour average, public warning when PM10 levels reach 420 µg/m3 on a 24 hour average, and a declaration of public emergency at the level of 500 µg/m3. The significant harm level, at which serious and widespread health effects occur to the general population, is 600 µg/m3 of PM10.

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