Air pollution occurs when wastes dirty the air. People produce most of the wastes
that cause air pollution. Such wastes can be in the form of gases or particulates
(particles of solid or liquid matter). These substances result chiefly from burning
fuel to power motor vehicles and to heat buildings. Industrial processes and the
burning of garbage also contribute to air pollution. Natural pollutants (impurities)
include dust, pollen, soil particles, and naturally occurring gases.
The rapid
growth of population and industry, and the increased use of automobiles and airplanes,
have made air pollution a serious problem. The air we breathe has become so filled
with pollutants that it can cause health problems. Polluted air also harms plants,
animals, building materials, and fabrics. In addition, it causes damage by altering
the earth's atmosphere.
The
damage caused by air pollution costs the people of the United States billions of dollars
each year. This includes money spent for health care and increased maintenance of
buildings. Air pollution also causes damage to the environment that cannot be
reversed.
Chief
sources of air pollution
People
depend on the atmosphere to dilute and remove pollutants as they are produced. But
weather conditions called thermal inversions can trap the pollutants over a certain area
until they build up to dangerous levels. A thermal inversion occurs when a layer of
warm air settles over a layer of cool air that lies near the ground. This condition
traps the impurities and prevents them from rising until rain or wind breaks up the layer
of stationary warm air.
Forms of
transportation, such as automobiles, airplanes, ships, and trains, are the leading source
of air pollution in the United States, Canada, and most other industrial nations.
The major pollutants produced by these sources are carbon monoxide, carbon dioxide,
hydrocarbons (compounds of carbon and hydrogen), and nitrogen oxides (compounds of
nitrogen and oxygen). Nitrogen oxides can react with hydrocarbons in the presence of
sunlight to produce a form of oxygen called ozone. Ozone is the chief component of
photochemical smog, which is a common form of air pollution (see SMOG).
Fuel combustion
for heating and cooling homes, office buildings, and factories contributes significantly
to air pollution. Electric power plants that burn coal or oil also release
pollutants into the atmosphere. The major pollutants from these sources are nitrogen
oxides, sulfur oxides (compounds of sulfur and oxygen), particulates, and carbon
dioxide.
Industrial
processes produce a wide range of pollutants. Oil refineries discharge ammonia,
hydrocarbons, organic acids, and sulfur oxides. Metal smelting plants give off large
amounts of sulfur oxides and particulates containing lead and other metals. Plants
that make aluminum expel fluoride dust. Plants that produce plastic foams are a
major source of chlorofluorocarbons (CFC's), compounds of chlorine, fluorine, and
carbon. By 1996, most industrialized countries, including the United States, had
ended production of CFC's.
Burning of
solid wastes often creates a very visible form of air pollution--thick, black smoke.
The burning of garbage, leaves, and other refuse is banned in most parts of the United
States and Canada.
Other
sources of pollution include chemical sprays and organic chemicals used to start fires on
charcoal grills. Forest fires and structural fires also contribute to air
pollution. In rural areas and in developing countries, the burning of forests and
grasslands to clear areas for farming is a major source of air pollution.
Natural
sources also contribute to air pollution. Volcanoes emit large amounts of sulfur
oxides and particulates. Microbes in the guts of cattle and in rice paddies break
down plant materials and release an odorless gas called methane, a type of
hydrocarbon.
Indoor
air pollution occurs when energy-efficient houses and office buildings trap pollutants
inside. As a result, some pollutants found outdoors are found indoors in even higher
concentrations. Some plastic products, processed wood products, paints, and
adhesives can give off hydrocarbons. Many cleaning products emit poisonous gases
such as ammonia and chlorine. An odorless gas called radon is released into the
atmosphere from soil and rocks. It enters buildings through cracks in the foundation
(see RADON).
Effects
of air pollution
Health.
When people breathe polluted air, the impurities can irritate their air passages and their
lungs. Particulates often remain in the lungs and can worsen such respiratory
ailments as asthma and bronchitis. Radon can cause lung cancer if inhaled in large
quantities. Certain chemical compounds can cause cancer and birth defects.
Ozone can aggravate emphysema and reduces resistance to colds and pneumonia. In
addition, carbon monoxide interferes with the transfer of oxygen from the lungs to body
tissues.
In London in
1952, about 4,000 people died of respiratory diseases during a "killer
smog." More than 600 people died as a result of thermal inversions that
occurred in New York City in 1953 and 1963. Today, such extreme events are rare
because of government emission standards, which limit pollutants released by factories and
other sources. However, air pollution still contributes to a large number of deaths
each year.
Agriculture.
Air pollutants can stunt the growth of crops, harm livestock, and destroy crops as
well. Such damage costs the United States millions of dollars each year.
Forests also have been damaged by air pollution.
Atmosphere.
Some pollutants are not poisonous but can cause damage by altering the earth's
atmosphere. For example, the amount of carbon dioxide in the atmosphere has been
increasing since the early to mid-1800's, chiefly as a result of the burning of coal, oil,
and other carbon-containing fuels. Carbon dioxide allows sunlight to reach the earth
and warm its surface, but it prevents some surface heat from escaping out of the
atmosphere. This greenhouse effect may produce significant climatic changes, which
could destroy many kinds of plants and animals.
Chlorofluorocarbons
break down the layer of ozone in the earth's upper atmosphere. This layer protects
plants and animals from harmful ultraviolet rays (see OZONE).
Other
effects. Most materials deteriorate faster when exposed to the pollutants present in
the air. Concrete and stone are dissolved by air pollutants. Metals corrode
faster than usual. Plastics, rubber, and fabrics are also damaged by air
pollutants.
Air
pollution is closely related to other forms of pollution. Sulfur dioxide and
nitrogen oxides can react with water droplets in the air to produce acid rain. Acid
rain pollutes lakes and streams and, in high concentrations, can harm soil fertility
Control
of air pollution
In the
United States, all levels of government--federal, state, and local--have passed laws
designed to control pollution. Congress passed the Air Quality Act in 1967.
Under this act, the federal government sets goals called air quality standards for
achieving cleaner air. The states must enforce air pollution controls to meet the
goals. When states fail to enforce the regulations, the federal government can act
against the polluters by imposing fines. However, the lack of funding to enforce
these regulations has allowed some polluters to continue releasing harmful pollutants for
years.
States may set
stricter air standards than the federal government requires. Since 1970, California
has set the strictest standards for motor-vehicle emissions. Stricter nationwide
standards for emissions have been repeatedly postponed because of opposition from
automobile industry groups.
Pollution
from automobiles has been reduced by changes in motor vehicles. Since 1975, most
American-made cars have been equipped with pollution-control devices called catalytic
converters. Devices called scrubbers have been installed in many electric power
plants, factories, and incinerators, to remove sulfur oxides and some other pollutants
before they reach the air. Pollution can also be reduced by increasing energy
efficiency and burning less fuel. In addition, recycling reuses some wastes that
otherwise might have been burned.
Efforts to
control air pollution in the United States have had some success. But many urban
areas fail to meet federal air quality standards. Since 1970, emissions of sulfur
oxides, hydrocarbons, and carbon monoxide have decreased by 25 to 40 percent. But
emissions of nitrogen oxides have increased slightly. Emissions of lead have fallen
about 96 percent, mostly because lead has been phased out of gasoline.
In 1990,
the U.S. Congress amended the Clean Air Act of 1970. The amendments set stricter
standards for air quality and emissions, require the sale of cleaner burning fuels, and
call for cuts in sulfur dioxide emissions from power plants to reduce acid rain. In
1989, a plan took effect to help the Los Angeles area meet federal air quality standards
by 2007.
In other
countries. The lack of controls on automobile emissions in Western Europe has
contributed to extensive damage to forests there. Countries in Eastern Europe have
lacked pollution controls altogether and have suffered enormous environmental damage as a
result. Protecting the environment will require international cooperation. |
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