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.
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.
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
Air Pollution at Shenandoah
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.