Atmospheric (Air) Pollutants

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Atmospheric (air) pollutants

Atmospheric pollutants are substances that accumulate in the air to a degree that is harmful to living organisms or to materials exposed to the air. Common air pollutants include smoke , smog , and gases such as carbon monoxide , nitrogen and sulfur oxides, and hydrocarbon fumes. While gaseous pollutants are generally invisible, solid or liquid pollutants in smoke and smog are easily seen. One particularly noxious form of air pollution occurs when oxides of sulfur and nitrogen combine with atmospheric moisture to produce sulfuric and nitric acid . When the acids are brought to Earth in the form of acid rain , damage is inflicted on lakes, rivers, vegetation, buildings, and other objects. Because sulfur and nitrogen oxides can be carried for long distances in the atmosphere before they are removed in precipitation, damage may occur far from pollution sources.

Smoke is an ancient environmental pollutant, but increased use of fossil fuels in recent centuries has increased its severity. Smoke can aggravate symptoms of asthma , bronchitis , and emphysema , and long term exposure can lead to lung cancer . Smoke toxicity increases when fumes of sulfur dioxide , commonly released by coal combustion , are inhaled with it. One particularly bad air pollution incident occurred in London in 1952 when approximately 4,000 deaths resulted from high smoke and sulfur dioxide levels that accumulated in the metropolitan area during an atmospheric inversion .

Sources of air pollutants are particularly abundant in modem, industrial population centers. Major sources include power and heating plants, industrial manufacturing plants, and transportation vehicles. Mexico City is a particularly bad example of a very large metropolitan area that has not adequately controlled harmful emissions into the atmosphere, and as a result many area residents suffer from respiratory ailments. The Mexican government has been forced to shut down a large oil refinery and ban new polluting industries from locating in the city. More difficult for the Mexican government to control are the emissions from over 3.5 million automobiles, trucks, and buses.

Smog (a combination of smoke and fog) is formed from the condensation of moisture (fog) on particulate matter (smoke) in the atmosphere. Although smog has been present in urban areas for a long time, photochemical smog is an exceptionally harmful and annoying form of air pollution found in large urban areas. It was first recognized as a serious problem in Los Angeles in the late 1940s. Photochemical smog forms by the catalytic action of sunlight on some atmospheric pollutants including unburned hydrocarbons evaporated from automobile and other fuel tanks. Products of the photochemical reactions include ozone , aldehydes, ketones , peroxyacetyl nitrate , and organic acids. Photochemical smog causes serious eye and lung irritation and other health problems.

Because of the serious damage caused by atmospheric pollution, control has become a high priority in many countries. Several approaches have proven beneficial. An immediate control measure involves a system of air alerts announced when air pollution monitors disclose dangerously high levels of contamination. Industrial sources of pollution are forced to curtail activities until conditions return to normal. These emergency situations are often caused by atmospheric inversions that limit the upward mixing of pollutants. Wider dispersion of pollutants by taller smokestacks can alleviate local pollution. However, dispersion does not lessen overall amounts; instead, it can create problems for communities downwind from the source. Greater energy efficiency in vehicles, homes, electrical power plants , and industrial plants, lessens pollution from these sources. This reduction in fuel use also reduces pollution created when fuels are produced, and as an added benefit, more energy efficient operation reduces costs. Efficient and convenient mass transit also helps to mitigate urban air pollution by cutting the need for personal vehicles.

[Douglas C. Pratt ]

RESOURCES

BOOKS

Georgii, H. W., ed. Atmospheric Pollutants in Forest Areas: Their Deposition and Interception. Boston: Kluwer Academic Publishers, 1986.

Hutchinson, T. C., and K. M. Meema, eds. Effects of Atmospheric Pollutants on Forests, Wetlands, and Agricultural Ecosystems. New York: Springer-Verlag, 1987.

Restelli, G., and G. Angeletti, eds. Physico-Chemical Behaviour of Atmospheric Pollutants. Boston: Kluwer Academic Publishers, 1990.