Air Pollution

Factories and transportation depend on huge amounts of fuel billions of tons of coal and oil are consumed around the world every year. When these fuels burn they introduce smoke and other, less visible, by-products into the atmosphere. Although wind and rain occasionally wash away the smoke given off by power plants and automobiles, the cumulative effect of air pollution poses a grave threat to humans and the environment.

In many places smoke from factories and cars combines with naturally occurring fog to form smog. For centuries, London, England, has been subjected to the danger of smog, long recognized as a potential cause of death, especially for elderly persons and those with severe respiratory ailments. Air pollution in London originally resulted from large-scale use of heating fuels. (See also City, "City Climates.")

A widespread awareness of air pollution dates from about 1950. It was initially associated with the Los Angeles area. The Los Angeles Basin is ringed for the most part by high mountains. As air sinks from these mountains it is heated until it accumulates as a warm layer that rises above the cooler air from the Pacific Ocean. This results in a temperature inversion, with the heavier cool air confined to the surface. Pollutants also become trapped at surface levels. Because of air-circulation patterns in the Los Angeles Basin, polluted air merely moves from one part of the basin to another part.

Scientists believe that all cities with populations exceeding 50,000 have some degree of air pollution. Burning garbage in open dumps causes air pollution. Other sources include emissions of sulfur dioxide and other noxious gases by electric power plants that burn high-sulfur coal or oil. Industrial boilers at factories also send large quantities of smoke into the air. The process of making steel and plastic generates large amounts of smoke containing metal dust or microscopic particles of complex and sometimes even deadly chemicals.

The single major cause of air pollution is the internal-combustion engine of automobiles. Gasoline is never completely burned in the engine of a car, just as coal is never completely burned in the furnace of a steel mill. Once they are released into the air, the products of incomplete combustion particulate matter (soot, ash, and other solids), unburned hydrocarbons, carbon monoxide, sulfur dioxide, various nitrogen oxides, ozone, and lead undergo a series of chemical reactions in the presence of sunlight. The result is the dense haze characteristic of smog. Smog may appear brownish in color when it contains high concentrations of nitrogen dioxide, or it may look blue-grey when it contains large amounts of ozone. In either case, prolonged exposure will damage lung tissue.

The costs of air pollution are enormous. The American Lung Association sites sulfur-dioxide exposure as the third leading cause of lung disease after active and passive smoking. Contaminants in the air also have been implicated in the rising incidence of asthma, bronchitis, and emphysema, a serious and debilitating disease of the lung's air sacs.

In the mid-1970s, people became aware of the phenomenon called acid rain (see Acid Rain). When sulfur dioxide emissions from electric power plants combine with particles of water in the atmosphere, they fall to ground as acid rain or snow. The acidity or basicity of liquids, including rainfall and snow, is measured by a special scale, called the pH scale. Developed in 1909 by the Danish biochemist S.P.L. Sorensen, the pH scale is used to describe the concentration of electrically charged hydrogen atoms in a water solution. A pH of 7.0 means that the solution is neutral. A pH above 7.0 means the solution is basic; below 7.0 means the solution is acidic. Normal rainwater has a pH of 5.5. The National Center for Atmospheric Research has recorded storms in the northeastern United States with a pH of 2.1, which is the acidity of lemon juice or vinegar. In Canada, Scandinavia, and the northeastern United States, acid rain is blamed for the deaths of thousands of lakes and streams. These lakes have absorbed so much acid rain that they can no longer support the algae, plankton, and other aquatic life that provide food and nutrients for fish. Acid rain also damages buildings and monuments. Scientists are concerned that the deaths of thousands of trees in the forests of Europe, Canada, and the United States may be the result of acid rain.

Another new and troubling form of air pollution comes from a variety of chemicals called chlorofluorocarbons, also known as CFCs. These chemicals are used for many industrial purposes, ranging from solvents used to clean computer chips to the refrigerant gases found in air conditioners and ice boxes. CFCs combine with other molecules in the Earth's upper atmosphere and then, by attaching themselves to molecules of ozone, transform and destroy the protective ozone layer. The result has been a sharp decline in the amount of ozone in the stratosphere. At ground level, ozone is a threat to our lungs, but in the upper atmosphere ozone works as a shield to protect against ultraviolet radiation from the sun. If the ozone shield gets too thin or disappears, exposure to ultraviolet radiation can cause crop failures and the spread of epidemic diseases, skin cancer, and other disasters. In late 1987, more than 20 nations signed an agreement to limit the production of CFCs and to work toward their eventual elimination.

Air pollution has been the target of some of the most complicated and far-reaching legislation ever enacted. In 1970, the United States Congress passed legislation aimed at curbing sources of air pollution and setting standards for air quality. A few years later, Congress passed laws designed to phase out the use of lead as an additive in gasoline. Since 1975, the level of lead in the average American's bloodstream has declined. Further action against the causes of acid rain is continually debated in North America and throughout Europe.

Although the release of toxic chemicals into the atmosphere is against the law in most countries, accidents can happen, often with tragic results. In 1984, in Bhopal, India, a pesticide manufacturing plant released a toxic gas into the air that within a few hours caused the deaths of more than 2,000 people.

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Excerpted from Compton's Interactive Encyclopedia

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