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8 May, 1996
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
their 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 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
lead 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.
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
where 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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Air pollution, Environmental chemistry, Smog, Industrial gases, Greenhouse gases, Ozone, Clean Air Act, Pollution, Acid rain, Pollutant, Sulfur dioxide, Carbon dioxide
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