Particulate Matter (PM)
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Nature and Sources of the Pollutant: Particulate matter is the general term used for a mixture of solid particles and liquid droplets found in the air. Some particles, are large or dark enough to be seen as soot or smoke. Others are so small they can be detected only with an electron microscope. These particles, which come in a wide range of sizes ("fine" particles are less than 2.5 micrometers in diameter and "coarse" particles are larger than 2.5 micrometers), originate from many different stationary and mobile sources as well as from natural sources. Fine particles (PM2.5) result from fuel combustion from motor vehicles, power generation, and industrial facilities, as well as from residential fireplaces and wood stoves. Coarse particles (PM10) are generally emitted from sources such as vehicles traveling on unpaved roads, materials handling, and crushing and grinding operations, as well as windblown dust. Some particles are emitted directly from their sources such as smokestacks and cars. In other cases, gases such as sulfur oxide and SO2, NOx, and VOC interact with other compounds in the air to form PM. Their chemical and physical compositions vary depending on location, time of year, and meteorology.
Health and Environmental Effects: Scientific studies show a link between PM (alone, or combined with other pollutants in the air) and a series of significant health effects. These health effects include premature death, increased hospital admissions and emergency room visits, increased respiratory symptoms and disease, decreased lung function, and alterations in lung tissue and structure and in respiratory tract defense mechanisms. Sensitive groups that appear to be at greater risk to such effects include the elderly, individuals with cardiopulmonary disease such as asthma, and children. In addition to health problems, PM is the major cause of reduced visibility in many parts of the U.S. Airborne particles also can cause soiling and damage to materials.
The New Fine Particle (PM2.5) Standards: After an extensive scientific and public process, EPA announced revisions to the PM national ambient air quality standards in July 1997. The review of hundreds of peer-reviewed scientific studies, published since the original PM standards were established, provided strong evidence that significant health effects are associated with exposures to ambient levels of fine particles allowed by the PM10 standards. Consistent with the advice given by a panel of outside scientific experts known as the Clean Air Scientific Advisory Committee, EPA determined that adding new standards was necessary to protect the health of the public and the environment. The primary health-based standards were revised to add two new PM2.5 standards, set at 15 g/m3 and 65 g/m3, respectively, for the annual and 24-hour standards, and to change the form of the 24-hour PM10 standard.
Trends in PM10 Levels: Air monitoring networks were changed in 1987 to measure PM10 (replacing the earlier Total Suspended Particle monitors). Between 1988 and 1996, average PM10 concentrations decreased 25 percent. Short-term trends between 1996 and 1996 showed a decrease of 4 percent in monitored PM10 concentration levels.
Emissions of PM10 shown in the chart are based on estimates from fuel combustion sources, industrial processes, and transportation sources, which account for only 6 percent of the total PM10 emissions nationwide. Between 1988 and 1996, PM10 emissions for these sources decreased 12 percent. Short-term emissions trends between 1996 and 1996 remained unchanged.
The emissions estimates presented below do not include emissions from natural and miscellaneous sources which are fugitive dust (unpaved and paved roads), agricultural and forestry activities, wind erosion, wildfires and managed burning. These emissions estimates also do not account for PM that is secondarily formed in the atmosphere from gaseous pollutants (i.e., SO2 and NOx).