Air Pollution is addition of harmful substances to the atmosphere resulting in
damage to the environment, human health, and quality of life. One of many forms
of pollution, air pollution occurs inside homes, schools, and offices; in
cities; across continents; and even globally. Air pollution makes people sick,
it causes breathing problems and promotes cancer, and it harms plants, animals,
and the ecosystems in which they live. Some air pollutants return to earth in
the form of acid rain and snow, which corrode statues and buildings, damage
crops and forests, and make lakes and streams unsuitable for fish and other
plant and animal life. Pollution is changing the earth's atmosphere so that it
lets in more harmful radiation from the sun. At the same time, our polluted
atmosphere is becoming a better insulator, preventing heat from escaping back
into space and leading to a rise in global average temperatures. Scientists
predict that the temperature increase, referred to as global warming, will
affect world food supply, alter sea level, make weather more extreme, and
increase the spread of tropical disease. Most air pollution comes from one human
activity: burning fossil fuels, natural gas, coal, and oil to power industrial
processes and motor vehicles. Among the harmful chemical compounds this burning
puts into the atmosphere are carbon dioxide, carbon monoxide, nitrogen oxides,
sulfur dioxide, and tiny solid particles including lead from gasoline additives
called particulates. Between 1900 and 1970, motor vehicle use rapidly expanded,
and emissions of nitrogen oxides, some of the most damaging pollutants in
vehicle exhaust, increased 690 percent. When fuels are incompletely burned,
various chemicals called volatile organic chemicals also enter the air.
Pollutants also come from other sources. For instance, decomposing garbage in
landfills and solid waste disposal sites emits methane gas, and many household
products give off Volatile organic chemicals. Some of these pollutants also come
from natural sources. For example, forest fires emit particulates and Volatile
organic chemicals into the atmosphere. Ultrafine dust particles, dislodged by
soil erosion when water and weather loosen layers of soil, increase airborne
particulate levels. Volcanoes spew out sulfur dioxide and large amounts of
pulverized lava rock known as volcanic ash. A big volcanic eruption can darken
the sky over a wide region and affect the earth's entire atmosphere. The 1991
eruption of Mount Pinatoubo in the Philippines, for example, dumped enough
volcanic ash into the upper atmosphere to lower global temperatures for the next
two years. Unlike pollutants from human activity, however, naturally occurring
pollutants tend to remain in the atmosphere for a short time and do not lead to
permanent atmospheric change. Once in the atmosphere, pollutants often undergo
chemical reactions that produce additional harmful compounds. Air pollution is
subject to weather patterns that can trap it in valleys or blow it across the
globe to damage pristine environments far from the original sources. Local and
regional pollution take place in the lowest layer of the atmosphere, the
troposphere, which extends from the earth's surface to about ten miles . The
troposphere is the region in which most weather occurs. If the load of
pollutants added to the troposphere were equally distributed, the pollutants
would be spread over vast areas and the air pollution might almost escape our
notice. Pollution sources tend to be concentrated, however, especially in
cities. In the weather phenomenon known as thermal inversion, a layer of cooler
air is trapped near the ground by a layer of warmer air above. When this occurs,
normal air mixing almost ceases and pollutants are trapped in the lower layer.
Local topography, or the shape of the land, can worsen this effect, an area
ringed by mountains, for example, can become a pollution trap. Smog is intense
local pollution usually trapped by a thermal inversion. Before the age of the
automobile, most smog came from burning coal and was so severe that in
19th-century London, street lights were turned on by noon because soot and smog
darkened the midday sky. Burning gasoline in motor vehicles is the main source
of smog in most regions today. Powered by sunlight, oxides of nitrogen and
volatile organic compounds react in the atmosphere to produce photochemical
smog. Smog contains ozone, a form of oxygen gas made up of molecules with three
oxygen atoms rather than the normal two. Ozone in the lower atmosphere is a
poison; it damages vegetation, kills trees, irritates lung tissues, and attacks
rubber. Environmental officials measure ozone to determine the severity of smog.
When the ozone level is high, other pollutants, including carbon monoxide, are
usually present at high levels as well. In the presence of atmospheric moisture,
sulfur dioxide and oxides of nitrogen turn into droplets of pure acid floating
in smog. These airborne acids are bad for the lungs and attack anything made of
limestone, marble, or metal. In cities around the world, smog acids are eroding
precious artifacts, including the Parthenon temple in Athens, Greece, and the
Taj Mahal in Agra, India. Oxides of nitrogen and sulfur dioxide pollute places
far from the points where they are released into the air. Carried by winds in
the troposphere, they can reach distant regions where they descend in acid form,
usually as rain or snow. Such acid precipitation can burn the leaves of plants
and make lakes too acidic to support fish and other living things. Because of
acidification, sensitive species such as the popular brook trout can no longer
survive in many lakes and streams in the eastern United States. Smog spoils
views and makes outdoor activity unpleasant. For the very young, the very old,
and people who suffer from asthma or heart disease, the effects of smog are even
worse: It may cause headaches or dizziness and can cause breathing difficulties.
In extreme cases, smog can lead to mass illness and death, mainly from carbon
monoxide poisoning. In 1948 in the steel-mill town of Donora, Pennsylvania,
intense local smog killed nineteen people. In 1952 in London over 3000 people
died in one of the notorious smog events known as London Fogs; in 1962 another
700 Londoners died. With stronger pollution controls and less reliance on coal
for heat, today's chronic smog is rarely so obviously deadly. However, under
adverse weather conditions, accidental releases of toxic substances can be
equally disastrous. The worst such accident occurred in 1984 in Bhopal, India,
when methyl isocyanate released from an American-owned factory during a thermal
inversion caused at least 3300 deaths. Air pollution can expand beyond a
regional area to cause global effects. The stratosphere is the layer of the
atmosphere between ten miles and thirty miles above sea level. It is rich in
ozone, the same molecule that acts as a pollutant when found at lower levels of
the atmosphere in urban smog. Up at the stratospheric level, however, ozone
forms a protective layer that serves a vital function: it absorbs the wavelength
of solar radiation known as ultraviolet-B (UV-B). UV-B damages deoxyribonucleic
acid (DNA), the genetic molecule found in every living cell, increasing the risk
of such problems as cancer in humans. Because of its protective function, the
ozone layer is essential to life on earth. Several pollutants attack the ozone
layer. Chief among them is the class of chemicals known as chlorofluorocarbons
(CFCs), used as refrigerants (notably in air conditioners), as agents in several
manufacturing processes, and formerly as propellants in spray cans. CFC
molecules are virtually indestructible until they reach the stratosphere. Here,
intense ultraviolet radiation breaks the CFC molecules apart, releasing the
chlorine atoms they contain. These chlorine atoms begin reacting with ozone,
breaking it down into ordinary oxygen molecules that do not absorb UV-B. The
chlorine acts as a catalyst that is, it takes part in several chemical
reactions, yet at the end emerges unchanged and able to react again. A single
chlorine atom can destroy up to 100,000 ozone molecules in the stratosphere.
Other pollutants, including nitrous oxide from fertilizers and the pesticide
methyl bromide, also attack atmospheric ozone. Scientists are finding that under
this assault the protective ozone layer in the stratosphere is thinning. In the
Antarctic region, it vanishes almost entirely for a few weeks every year.
Although CFC use has been greatly reduced in recent years, CFC molecules already
released into the lower atmosphere will be making their way to the stratosphere
for decades, and further ozone loss is expected. As a result, experts anticipate
an increase in skin cancers, more cataracts (clouding of the lens of the eye),
and reduced yields of some food crops. Humans are bringing about another
global-scale change in the atmosphere: the increase in what are called
greenhouse gases. Like glass in a greenhouse, these gases admit the sun's light
but tend to reflect back downward the heat that is radiated from the ground
below, trapping heat in the earth's atmosphere. This process is known as the
greenhouse effect. Carbon dioxide is the most significant of these gases; there
is 25 percent more carbon dioxide in the atmosphere today than there was a
century ago, the result of our burning coal and fuels derived from oil. Methane,
nitrous oxide, and CFCs are greenhouse gases as well. Scientists predict that
increases in these gases in the atmosphere will make the earth a warmer place.
They expect a global rise in average temperature somewhere between 1.0º and 3.5º
C (1.8º and 6.3º F) in the next century. Average temperatures have in fact
been rising, and the years from 1987 to 1997 were the warmest ten years on
record. Most scientists are reluctant to say that global warming has actually
begun because climate naturally varies from year to year and decade to decade,
and it takes many years of records to be sure of a fundamental change. There is
little disagreement, though, that global warming is on its way. Global warming
will have different effects in different regions. A warmed world is expected to
have more extreme weather, with more rain during wet periods, longer droughts,
and more powerful storms. Although the effects of future climate change are
unknown, some predict that exaggerated weather conditions may translate into
better agricultural yields in areas such as the western United States, where
temperature and rainfall are expected to increase, while dramatic decreases in
rainfall may lead to severe drought and plunging agricultural yields in parts of
Africa, for example. Warmer temperatures are expected to partially melt the
polar ice caps, leading to a projected sea level rise of twenty inches by the
year 2050. A sea level rise of this magnitude would flood coastal cities, force
people to abandon low-lying islands, and completely inundate coastal wetlands.
If sea levels rise at projected rates, the Florida Everglades will be completely
under water in less than 50 years. Diseases like malaria, which at present are
primarily found in the tropics, may become more common in the regions of the
globe between the tropics and the polar regions, called the temperate zones. For
many of the world's plant species, and for animal species that are not easily
able to shift their territories as their habitat grows warmer, climate change
may bring extinction. Pollution is perhaps most harmful at an often unrecognized
site, inside the homes and buildings where we spend most of our time. Indoor
pollutants include tobacco smoke; radon, an invisible radioactive gas that
enters homes from the ground in some regions; and chemicals released from
synthetic carpets and furniture, pesticides, and household cleaners. When
disturbed, asbestos, a nonflammable material once commonly used in insulation,
sheds airborne fibers that can produce a lung disease called asbestosis.
Pollutants may accumulate to reach much higher levels than they do outside,
where natural air currents disperse them. Indoor air levels of many pollutants
may be 2 to 5 times, and occasionally more than 100 times, higher than outdoor
levels. These levels of indoor air pollutants are especially harmful because
people spend as much as 90 percent of their time living, working, and playing
indoors. Inefficient or improperly vented heaters are particularly dangerous. In
the United States, the serious effort against local and regional air pollution
began with the Clean Air Act of 1970, which was amended in 1977 and 1990. This
law requires that the air contain no more than specified levels of particulate
matter, lead, carbon monoxide, sulfur dioxide, nitrogen oxides, volatile organic
compounds, ozone, and various toxic substances. To avoid the mere shifting of
pollution from dirty areas to clean ones, stricter standards apply where the air
is comparatively clean. In national parks, for instance, the air is supposed to
remain as clean as it was when the law was passed. The act sets deadlines by
which standards must be met. The Environmental Protection Agency (EPA) is in
charge of refining and enforcing these standards, but the day-to-day work of
fighting pollution falls to the state governments and to local air pollution
control districts. Some states, notably California, have imposed tougher air
pollution standards of their own. In an effort to enforce pollution standards,
pollution control authorities measure both the amounts of pollutants present in
the atmosphere and the amounts entering it from certain sources. The usual
approach is to sample the open, or ambient, air and test it for the presence of
specified pollutants. The amount of each pollutant is counted in parts per
million or, in some cases, milligrams or micrograms per cubic meter. To learn
how much pollution is coming from specific sources, measurements are also taken
at industrial smokestacks and automobile tailpipes. Pollution is controlled in
two ways: with end-of-the-pipe devices that capture pollutants already created,
and by limiting the quantity of pollutants produced in the first place.
End-of-the-pipe devices include catalytic converters in automobiles and various
kinds of filters and scrubbers in industrial plants. In a catalytic converter,
exhaust gases pass over small beads coated with metals that promote reactions
changing harmful substances into less harmful ones. When end-of-the-pipe devices
first began to be used, they dramatically reduced pollution at a relatively low
cost. As air pollution standards become stricter, it becomes more and more
expensive to further clean the air. In order to lower pollution overall,
industrial polluters are sometimes allowed to make cooperative deals. For
instance, a power company may fulfill its pollution control requirements by
investing in pollution control at another plant or factory, where more effective
pollution control can be accomplished at a lower cost. End-of-the-pipe controls,
however sophisticated, can only do so much. As pollution efforts evolve, keeping
the air clean will depend much more on preventing pollution than on curing it.
Gasoline, for instance, has been reformulated several times to achieve cleaner
burning. Various manufacturing processes have been redesigned so that less waste
is produced. Car manufacturers are experimenting with automobiles that run on
electricity or on cleaner-burning fuels. Buildings are being designed to take
advantage of sun in winter and shade and breezes in summer to reduce the need
for artificial heating and cooling, which are usually powered by the burning of
fossil fuels. The choices people make in their daily lives can have a
significant impact on the state of the air. Using public transportation instead
of driving, for instance, reduces pollution by limiting the number of
pollution-emitting automobiles on the road. During periods of particularly
intense smog, pollution control authorities often urge people to avoid trips by
car. To encourage transit use during bad-air periods, authorities in Paris,
France, make bus and subway travel temporarily free. Indoor pollution control
must be accomplished building by building or even room by room. Proper
ventilation mimics natural outdoor air currents, reducing levels of indoor air
pollutants by continually circulating fresh air. After improving ventilation,
the most effective single step is probably banning smoking in public rooms.
Where asbestos has been used in insulation, it can be removed or sealed behind
sheathes so that it won't be shredded and get into the air. Sealing foundations
and installing special pipes and pumps can prevent radon from seeping into
buildings. On the global scale, pollution control standards are the result of
complex negotiations among nations. Typically, developed countries, having
already gone through a period of rapid and dirty industrialization, are ready to
demand cleaner technologies. Less developed nations, hoping for rapid economic
growth, are less enthusiastic about pollution controls. They seek lenient
deadlines and financial help from developed countries to make the expensive
changes necessary to reduce pollutant emissions in their industrial processes.
Nonetheless, several important international accords have been reached. In 1988,
the United States and 24 other nations agreed in the Long-Range Transboundary
Air Pollution Agreement to hold their production of nitrogen oxides, a key
contributor to acid rain, to current levels. In the Montreal Protocol, adopted
in 1987 and strengthened in 1990 and 1992, most nations agreed to stop or reduce
the manufacture of CFCs. In 1992 the United Nations Framework Convention on
Climate Change negotiated a treaty outlining cooperative efforts to curb global
warming. The treaty, which took effect in March 1994, has been legally accepted
by 160 of the 165 participating countries. In December 1997 at the Third
Conference of the United Nations Framework Convention on Climate Change in
Japan, more than 160 nations formally adopted the Kyoto Protocol. This agreement
calls for industrialized nations to reduce their emissions of greenhouse gases
to levels 5 percent below 1990 emission levels between 2008 and 2012. The United
States, which releases more greenhouse gases than any other nation, has
traditionally been slow to support such strong measures. The U.S. Senate may be
reluctant to ratify the Kyoto Protocol because it does not require developing
countries, such as China and India, to meet similar emissions goals. All these
antipollution measures have helped stem the increase of global pollution
emission levels. Between 1970, when the Clean Air Act was passed, and 1995,
total emissions of the major air pollutants in the United States decreased by
nearly 30 percent. During the same 25-year period, the U.S. population increased
28 percent and vehicle miles traveled increased 116 percent. Air pollution
control is a race between the reduction of pollution from each source, such as a
factory or a car, and the rapid multiplication of sources. Smog in American
cities is expected to increase again as the number of cars and miles driven
continues to rise. Meanwhile, developing countries are building up their own
industries, and their citizens are buying cars as soon as they can afford them.
Ominous changes continue in the global atmosphere. New efforts to control air
pollution will be necessary as long as these trends continue.