Air Pollution - Its Nature, Sources, and Effects
John F. Mitchell - NPS Volunteer
Air pollution occurs in many forms but can generally be thought of as gaseous and particulate contaminants that are present in the earth's atmosphere. Gaseous pollutants include sulfur dioxide (SO2), nitrogen oxides (NOx), ozone (O3), carbon monoxide (CO), volatile organic compounds (VOC), hydrogen sulfide (H2S), hydrogen fluoride (HF), and various gaseous forms of metals. These pollutants are emitted from large stationary sources such as fossil fuel fired power plants, smelters, industrial boilers, petroleum refineries, and manufacturing facilities as well as from area and mobile sources. They are corrosive to various materials which causes damage to cultural resources, can cause injury to ecosystems and organisms, aggravate respiratory diseases, and reduce visibility.
Particulates come in both large and small or "fine" solid forms. Large particulates include substances such as dust, asbestos fibers, and lead. Fine particulates include sulfates (SO4) and nitrates (NO3). Important sources of particulates are power plants, smelters, mining operations, and automobiles. Asbestos and lead affect organisms, while sulfates and nitrates not only cause health problems, but also contribute to acid rain or acid deposition and a reduction in visibility. Particulate matter, a term sometimes used instead of particulates, refers to the mixture of solid particles and liquid droplets found in the air.
Toxic air pollutants are a class of chemicals which may potentially cause health problems in a significant way. The sources of toxic air pollutants include power plants, industries, pesticide application, and contaminated windblown dust. Persistent toxic pollutants, such as mercury, are of particular concern because of their global mobility and ability to accumulate in the food chain. More research is needed to fully understand the fate and effects of mercury and the many other toxic pollutants.
Primary pollutants are those that are emitted directly into the air from pollution sources. Secondary pollutants are formed when primary pollutants undergo chemical changes in the atmosphere. Ozone is an example of a secondary pollutant. It is formed when nitrogen oxides (NOx) and volatile organic compounds (VOCs) are mixed and warmed by sunlight. Ozone (O3) is a major component of what is often referred to as smog. The ozone which is present in the troposphere, or the atmosphere that is close to the ground, should not be confused with beneficial ozone that is located in the stratosphere or upper atmosphere. This beneficial ozone in the stratosphere helps protect the earth from harmful ultraviolet light from the sun.
Sources of Air Pollution
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.
Air Pollution Effects
The air is an important component of the natural system of a park in its own right. The presence of pollution in the atmosphere results directly in air quality degradation. Air pollution is also a critical factor affecting the quality of other environmental resources as well as the human-made structures and facilities in the area. Polluted air can and has harmed park resources in a variety of ways depending upon the chemistry of the pollutant, weather and environmental conditions, and the nature or sensitivity of park resources. Examples of this harm include vegetative discoloration and growth disruption from ozone, loss of aquatic species from stream acidification, shifts in nutrient availability from acid deposition, and erosion of building surfaces and rock formations. Air pollution impairs visibility and contributes to climate change. Air pollution can also be detrimental to human health.
Additional information about the most significant air pollution related problems at Shenandoah may be found through the following links:
The following references may be helpful in understanding the effects of air pollutants:
Anon. 1973. Air pollution damages trees. Northeastern Area State and Private Forestry, Forest Service, U.S. Department of Agriculture. Upper Darby, Pennsylvania.
Anon. 2002. Air quality in the National Parks. Air Resources Division, National Park Service. Denver, Colorado.
Barker, J.R. and D.T. Tingey. 1992. Air pollution effects on biodiversity. Van Nostrand Reinhold, New York, New York.
Louma, J.R. and K.C. Joyner. 1990. Air pollution and forest decline: is there a link? Agriculture Information Bulletin 595. Forest Service, U.S. Department of Agriculture. Washington, DC.
Skelly, J.M. et al. 1987. Diagnosing injury to eastern forest trees. Forest Service, U.S. Department of Agriculture and The Pennsylvania State University, University Park, Pennsylvania.
The following websites provide information about air pollutants and terms used to describe them:
Listing of these websites does not and is not intended to imply endorsement by the National Park Service of commercial services or products associated with the sites.