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					                                           Air Pollution
                                                      the coal, oil, wood and other fuels we use to run
What Is Air Pollution?                                factories, cars and power plants that generate
The natural composition of air is mostly              heat and light for our homes.
nitrogen and oxygen, along with water droplets,
fine particles, and small amounts of other gases      Once pollutants are added to the air, they can
such as carbon dioxide, nitrous oxide, methane,       chemically react to form more dangerous
ammonia and argon. These gases can be either          pollutants. The interaction of nitrogen oxides
free in the air or associated with water vapor.       and other components near ground level in the
                                                      presence of sunlight forms another atmospheric
Air pollution is any visible or invisible particle    gas — ozone. Ozone has two very important but
or gas found in the air that is not part of the       different effects. The layer of ozone found in the
normal composition of air. Natural air pollution      upper atmosphere (stratosphere) provides a
has been around for millions of years, but            major protective barrier against harmful
during the last century, pollution created by         radiation from the sun. However, ozone near the
humans has become a major concern. While we           Earth’s surface can become a serious health
are most familiar with visible air pollution (such    problem when the ozone concentration becomes
as smog), many other air pollutants, including        too high, usually on long, sunny, summer days.
some of the most dangerous, are invisible.
                                                      Pollutants of any sort can ride the air currents
From Where Does Air Pollution                         for long distances. It has become very clear that
Come?                                                 the air around us and the pollutants it carries are
Natural air pollutants have always been part of       never just a local concern, but transcend
the Earth’s history. Particulate matter and a         regional, national and hemispheric boundaries.
variety of different gases from volcanoes, forest
fires and decaying organic materials in oceans        What Are the Effects of Air Pollution
and swamps enter the atmosphere at irregular          on Plants, Animals and Humans?
intervals, sometimes in amounts that have             Plant and animal life has adapted to most natural
dramatic effects. Naturally produced                  pollutants except for the rare catastrophic
“greenhouse” gases, such as methane from plant        occurrences that create worldwide climate
decay, may have contributed significantly to          changes. The most serious air quality concerns
periods of global warming in the past. Carbon         are the additional, often harmful, pollutants that
dioxide and water vapor react to form carbonic        humans add to the air.
acid, which makes rain slightly acidic even           Eventually, most of the water droplets carried
without pollution from other sources.                 by air fall to Earth as precipitation. Many of the
Naturally produced pollutants are present in          small particles and chemicals are washed from
greater amounts than those of human origin.           the atmosphere when precipitation falls. Air
However, they do not present as serious a             pollution then becomes land and water
problem as man-made pollutants because they           pollution, which can influence the structure and
are not concentrated over large cities and many       function of ecosystems, including their ability
are less harmful than man-made pollutants.            for self-regulation. Numerous small lakes in the
                                                      eastern U.S. are devoid of fish because of the
Air pollution from man-made sources is the            effects of “acid rain.”
result of our increasing use of large quantities of
fuel and high levels of industrial activity. Not      The impact of air pollution on humans is broad,
only are some of these pollutants very harmful,       causing symptoms ranging from itchy eyes to
but they also tend to be concentrated in urban        cancer. The absorption of inhaled chemicals can
areas in which many people live and work.             have direct consequences for health. However,
Many of these air pollutants come from burning        public health also can be indirectly affected by

Air Pollution: Lesson 1, Air Pollution Reading                                                          1
the deposition of air pollutants on plants,          How Do We Reduce Air Pollution?
animals and water. These chemicals, by entering      Since little can be done by humans about natural
the food chain or being present in drinking          pollution, our main concern has to be with the
water, constitute additional sources of human        additional pollutants from human activity.
exposure.                                            Because of the increasing concern over toxic
How Do We Detect Air Pollution?                      chemicals in the air we breathe, many laws have
                                                     been passed to control emission sources.
Every year, millions of tons of man-made
chemicals are released into the atmosphere,          Certain air pollutants are so pervasive that they
mostly by industrialized countries. However, the     show up wherever air quality is poor. Six have
toxic effects of these chemicals often are not       been designated criteria pollutants: particulate
recognized or understood until the chemicals         matter, sulfur dioxide, nitrogen dioxide, carbon
have been widely used for considerable periods       monoxide, ozone and lead. The U.S.
of time. A chemical compound that initially          Environmental Protection Agency set national
appears to have little or no effect on plants and    ambient air quality standards to protect health
animals may eventually produce extremely             and welfare in connection with these pollutants.
harmful results, often hidden for many years.        Where these standards are exceeded, the EPA
                                                     takes steps to control pollutant emissions.
DDT (dichlorodiphenyltrichloroethane) and
related chemicals are a classic case of such a       Identification and control of other hazardous air
situation. DDT is a very effective insecticide       pollutants are critical steps to controlling air
that showed great promise for fighting harmful       quality. Seven hazardous materials (arsenic,
insects all over the world. It was not until after   asbestos, benzene, beryllium, mercury, vinyl
many years of widespread use that DDT was            chloride and radionuclides) already have U.S.
discovered to have devastating toxic effects. A      standards. However, this start represents only a
high DDT level in bald eagles causes their eggs      very small portion of the entire hazardous waste
to be so thin-shelled that they are crushed during   problem. An expanded list of 189 hazardous
incubation. This results in a reduction in the       chemicals was identified for regulation and are
population, putting bald eagles on the               listed in the 1990 Clean Air Act Amendments.
endangered species list. Similar disastrous          Some states, even some cities, have been
repercussions can and are being repeated with        particularly aggressive in battling pollution of
other toxic chemicals in other food chains.          various sorts. New legislation is constantly
                                                     being discussed. Alternative energy sources and
Governments around the world have established
                                                     alternative strategies, such as mass transit and
programs to measure and monitor levels of
                                                     energy conservation, are all part of the solution.
airborne pollution. For many years, cities in the
                                                     Gradually, the international scope is being
U.S. developed and used their own indices for
                                                     recognized and international agreements are
reporting air pollution levels to the public.
                                                     being developed to try to address air quality
These individual indices have now been
                                                     problems on a global scale.
replaced by the Pollution Standards Index (PSI)
or the Air Quality Index (AQI), both recognized      Source: Project A.I.R.E. at
                                                     http://www.epa.gov/region01/students/teacher/airqual.html
as standardized measures that allow comparison
from city to city.




Air Pollution: Lesson 1, Air Pollution Reading                                                                   2

				
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