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Contamination of the atmosphere by gaseous, liquid, or solid wastes or by-products that can endanger human health and the health and welfare of plants and animals, or can attack materials, reduce visibility, or produce undesirable odors. Among air pollutants emitted by natural sources, only the radioactive gas radon is recognized as a major health threat. A byproduct of the radioactive decay of uranium minerals in certain kinds of rock, radon seeps into the basements of homes built on these rocks.
According to recent estimates by the U. S. government, 20 percent of the homes in the U. S. harbor radon concentrations that are high enough to pose a risk of lung cancer. Each year industrially developed countries generate billions of tons of pollutants. The level is usually given in terms of atmospheric concentrations or, for gases in terms of parts per million, that is, number of pollutant molecules per million air molecules. Many come from directly identifiable sources; sulfur dioxide, for example, comes from electric power plants burning coal or oil. Others are formed through the action of sunlight on previously emitted reactive materials.
For example, ozone, a dangerous pollutant in smog, is produced by the interaction of hydrocarbons and nitrogen oxides under the influence of sunlight. Ozone has also caused serious crop damage. On the other hand, the discovery in the 1980s that air pollutants such as fluorocarbons are causing a loss of ozone from the earth’s protective ozone layer has caused the phasing out of these materials. Current information about the problem The tall smokestacks used by industries an utilities do not remove pollutants but simply boost them higher into the atmosphere, thereby reducing heir concentration at the site.
These pollutants may then be transported over large distances and produce adverse effects in areas far from the site of the original emission. Sulfur dioxide and nitrogen oxide emissions from the central and eastern U. S. are causing acid rain in New York State, New England, and eastern Canada. The pH level, or relative acidity, of many freshwater lakes in that region has been altered so dramatically by this rain that entire fish populations have been destroyed. Similar effects have been observed in Europe.
Sulfur dioxide emissions and the subsequent formation of sulfuric acid can also be responsible for the attack on limestone and marble at large distances from the source. The worldwide increase in the burning of coal and oil since the late 1940s has led to ever increasing concentrations of carbon dioxide. The resulting “greenhouse effect”, which allows solar energy to enter the atmosphere but reduces the remission of infrared radiation from the earth, could conceivably lead to a warning trend that might affect the global climate and ead to a partial melting of the polar ice caps.
Possibly an increase in cloud cover or absorption of excess carbon dioxide by the oceans would check the greenhouse effect before it reached the stage of polar melting. Nevertheless, research reports released in the U. S. in the 1980s indicate that the greenhouse effect is definitely under way and that the nations of the world should be taking immediate steps to deal with it. History In the U. S. the Clean Air Act of 1967 as amended in 1970, 1977, and 1990 is the legal basis for air-pollution control throughout the U. S.
The Environmental Protection Agency has primary responsibility for carrying out the requirements of the act, which specifies that air-quality standards be established for hazardous substances. These standards are in the form of concentration levels that are believed to be low enough to protect public health. Source emission standards are also specified to limit the discharge of pollutants into the air so that air-quality standards will be achieved. The act was also designed to prevent significant deterioration of air quality in areas here the air is currently cleaner than the standards require.
The amendments of 1990 identify ozone, carbon monoxide, particulate matter, acid rain, and air toxins as major air pollution problems. On the international scene, 49 countries agreed in March 1985 on a United Nations convention to protect the ozone layer. This “Montreal Protocol,” which was renegotiated in 1990, calls for the phaseout of certain chlorocarbons and fluorocarbons by the year 2000 and provides aid to developing countries in making this transition.
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