Particulate Matter

Particulate matter is a leading pollutant responsible for declines in visibility throughout the United States. Particulate matter in the atmosphere includes wind-blown soil, soot, smoke, and liquid droplets. Sulfur dioxide, nitrogen oxides, and volatile organic compound gases can also be transformed, or condensed, in the atmosphere to form fine particles which are less than 2.5 microns in size (PM2.5). Emissions of particulate matter are estimated or measured either as total suspended particulates (TSP) or particulate matter 10 microns or less in size (PM10) (SAMAB 1996).

Nationally, the major area sources of particulate matter 10 microns or less in size (PM10) are fugitive dust emissions from unpaved roads, construction, agriculture crops, and from paved roads (EPA 1995). These major sources of particulates comprise only 8 percent of the total PM10 emissions nationwide. Nationally, between 1940 and 1994, particulate matter emissions from stationary sources have decreased significantly and are predicted to remain constant until the year 2010 (EPA 1995). However, the pattern could change if the number of acres burned from wildfires or prescribed fires increases significantly (SAMAB 1996).

In the southern Appalachians, violations of the particulate matter National Ambient Air Quality Standard have not occurred at any monitoring site. In fact, at most monitoring stations, particulate matter concentrations are well below current air quality standards (50 microns per cubic meter of air or 150 microns per cubic meter of air in any 24 hour period). New sources that emit small amounts, or even modest amounts, of particulate matter probably will not cause a violation of the annual standard. However, if the EPA revises its standards, prescribed fires may cause a violation of air quality standards. Particulate matter concentrations in the southern Appalachians are distributed fairly uniformly, but have some seasonal variation. Spring and summer mean concentrations are approximately 12 percent above the annual mean (SAMAB 1996).