Sources of Air Pollution
Stationary and Area Sources
A stationary source of air pollution refers to an emission source that does not move, also known as a point source. Stationary sources include factories, power plants, dry cleaners and degreasing operations. The term area source is used to describe many small sources of air pollution located together whose individual emissions may be below thresholds of concern, but whose collective emissions can be significant. Residential wood burners are a good example of a small source, but when combined with many other small sources, they can contribute to local and regional air pollution levels. Area sources can also be thought of as non-point sources, such as construction of housing developments, dry lake beds, and landfills.
A mobile source of air pollution refers to a source that is capable of moving under its own power. In general, mobile sources imply "on-road" transportation, which includes vehicles such as cars, sport utility vehicles, and buses. In addition, there is also a "non-road" or "off-road" category that includes gas-powered lawn tools and mowers, farm and construction equipment, recreational vehicles, boats, planes, and trains.
Agricultural operations, those that raise animals and grow crops, can generate emissions of gases and particulate matter. For example, animals confined to a barn or restricted area (rather than field grazing), produce large amounts of manure. Manure emits various gases, particularly ammonia into the air. This ammonia can be emitted from the animal houses, manure storage areas, or from the land after the manure is applied. In crop production, the misapplication of fertilizers, herbicides, and pesticides can potentially result in aerial drift of these materials and harm may be caused.
Although industrialization and the use of motor vehicles are overwhelmingly the most significant contributors to air pollution, there are important natural sources of "pollution" as well. Wildland fires, dust storms, and volcanic activity also contribute gases and particulates to our atmosphere.
Unlike the above mentioned sources of air pollution, natural "air pollution" is not caused by people or their activities. An erupting volcano emits particulate matter and gases; forest and prairie fires can emit large quantities of "pollutants"; plants and trees naturally emit VOCs which are oxidized and form aerosols that can cause a natural blue haze; and dust storms can create large amounts of particulate matter. Wild animals in their natural habitat are also considered natural sources of "pollution". The National Park Service recognizes that each of these sources emits gases and particulate matter into the atmosphere but we regard these as constituents resulting from natural processes.
Air Pollution at Shenandoah
Sources of air pollution that affect Shenandoah National Park are largely outside of the park. These include industrial facilities located throughout the mid-Atlantic region and the Ohio River Valley as well as urban centers in this same region. Because most areas adjacent to the park are rural and agricultural, it is clear that transport of pollutants from distant locations is an important element upon which park air quality hinges. Even some agricultural activities, such as ammonia from the poultry industry and pesticides that are applied to adjacent fields, may contribute to air pollution in the park. In-park emission sources are relatively small, but do include motor vehicles, maintenance equipment, small boilers and generators. The relative contribution from the in-park sources is very small compared to other sources. In a July 2002 report describing an emissions inventory for Shenandoah National Park, it was determined that less than 1% of emissions were produced from in-park sources.
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