Air Polution Essay Research Paper Air Pollution

  • Просмотров 189
  • Скачиваний 12
  • Размер файла 16

Air Polution Essay, Research Paper Air Pollution, 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 most prevalent and widely dispersed air pollutants are described in the accompanying table. The level is usually given in terms of atmospheric concentrations (micrograms of pollutants per cubic meter of air) 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 (called precursors). 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. Pollutant concentrates are reduced by atmospheric mixing, which depends on such weather conditions as temperature, wind speed, and the movement of high and low pressure systems and their interaction with the local topography, for example, mountains and valleys. Normally, temperature decreases with altitude. But when a colder layer of air settles under a warm layer, producing a temperature or thermal inversion, atmospheric mixing is retarded and pollutants may accumulate near the ground. Inversions can become sustained under a stationary high-pressure system coupled with low wind speeds.

Periods of only three days of poor atmospheric mixing can lead to high concentrations of hazardous materials in high-pollution areas and, under severe conditions, can result in injury and even death. An inversion over Donora, Pennsylvania, in 1948 caused respiratory illness in over 6000 persons and led to the death of 20. Severe pollution in London took 3500 to 4000 lives in 1952 and another 700 in 1962. Release of methyl isocyanate into the air during a temperature inversion caused the disaster at Bhopal, India, in December 1984, with at least 3300 deaths and more than 20,000 illnesses. The effects of long-term exposure to low concentrations are not well defined; however, those most at risk are the very young, the elderly, smokers, workers whose jobs expose them to toxic

materials, and persons with heart or lung disease. Other adverse effects of air pollution are potential injury to livestock and crops. Often, the first noticeable effects of pollution are aesthetic and may not necessarily be dangerous. These include visibility reduction due to tiny particles suspended in air, or bad odors, such as the rotten egg smell produced by hydrogen sulfide emanating from pulp and paper mills. Sources and Control The combustion of coal, oil, and gasoline accounts for much of the airborne pollutants. More than 80 percent of the sulfur dioxide, 50 percent of the nitrogen oxides, and 30 to 40 percent of the particulate matter emitted to the atmosphere in the U.S. are produced by fossil-fuel-fired electric power plants, industrial boilers, and residential