What is Acid Rain and What Causes It?
“Acid rain” is a broad term used to describe several ways that acids fall out of
the atmosphere. A more precise term is acid deposition, which has two parts:
wet and dry.
Wet deposition refers to acidic rain, fog, and snow. As this acidic water flows
over and through the ground, it affects a variety of plants and animals. The
strength of the effects depend on many factors, including how acidic the water
is, the chemistry and buffering capacity of
the soils involved, and the types of
fish, trees, and other living th
ings that rely on the water.
Dry deposition refers to acidic gases and
particles. About half of the acidity in
the atmosphere falls back to Earth through dry deposition. The wind blows
these acidic particles and gases onto buildings, cars, homes, and trees. Dry
deposited gases and particles can also be washed from trees and other
surfaces by rainstorms. When that happens, the runoff water adds those acids
to the acid rain, making the combinat
ion more acidic than the falling rain
alone.
Prevailing winds blow the compounds that cause both wet and dry acid
deposition across state and national borders, and sometimes over hundreds
of miles. Scientists discovered, and ha
ve confirmed, that sulfur dioxide (SO
2
)
and nitrogen oxides (NO
x
10
Ways of reducing the harmful
effects of acid deposition
Awareness is being generated among the masses worldwide about acid rain
and its harmful effects. This in turn would lead to the politicians being
provided with more and better solutions as well as being pressurized to take
effective steps to control acid rain. The following are a few steps that could be
taken in this regard:
Clean up smokestacks and exhaust pipes:
Almost all of the electricity that
powers modern life comes from burning fossil fuels like coal, natural gas, and
oil. Acid deposition is caused by two pollutants that are released into the
atmosphere, or emitted, when these fuels are burned: sulfur dioxide (SO
2
) and
nitrogen oxides (NO
x
).
Coal accounts for most for most of the sulfur dioxide (SO
2
) emissions and a
large portion of NO
x
emissions. Sulfur is present in coal as an impurity, and it
reacts with air when the coal is burned to form SO
2
. In contrast, NO
x
is formed
when any fossil fuel is burned.
There are several options for reducing SO
2
emissions, including using coal
containing less sulfur, washing the coal, and using devices called scrubbers to
chemically remove the SO
2
from the gases leaving the smokestack. Power
plants can also switch fuels; for example burning natural gas creates much
less SO
2
than burning coal. Certain approaches will also have additional
benefits of reducing other pollutants such as mercury and carbon dioxide.
Understanding these co-benefits has become important in seeking cost-
effective air pollution reduction strategies. Finally, power plants can use
technologies that don't burn fossil fuels. But each of these options has its own
costs and benefits. Similar to scrubbers on power plants, catalytic converters
reduce NO
x
emissions from cars.
Use alternative energy sources:
There are other sources of electricity
besides fossil fuels. They include: nu
clear power, hydropower, wind energy,
geothermal energy, and solar energy. Of these, nuclear and hydropower are
used most widely. Wind, solar, and geothermal energy have not yet been
harnessed on a large scale, but are potential alternatives.
There are also alternative energies available to power automobiles, including
natural gas powered vehicles, battery-powered cars, fuel cells, and
combinations of alternative and gasoline powered vehicles.
All sources of energy have environmental costs as well as benefits. Some
types of energy sources are more expensive to harness than others, which
means that not all people can afford all types of energy. Nuclear power,
hydropower, and coal are the cheapest forms today, but changes in
technologies and environmental regulations may shift that in the future. All of
these factors must be weighed when deciding which energy source to use
today and which to invest in for tomorrow
) are the primary causes of acid rain. Almost all of
SO
2
and some NO
x
come from electric power generation that relies on
burning fossil fuels like coal.
Acid rain occurs when these gases react in the atmosphere with water,
oxygen, and other chemicals to form various acidic compounds. Sunlight
increases the rate of most of these reactions. The result is a mild solution of
sulfuric acid and nitric acid.
Acid rain is measured using a scale called pH. The lower a substance's pH,
the more acidic it is. Pure water has a pH
of 7.0, which is neutral. Normal rain
is slightly acidic because carbon dioxide dissolves into it, so it has a pH of
about 5.5. In the year 2000, the most acidic rain falling in North America had a
pH of about 4.3.
Effects of Acid Rain
Acid rain causes acidification of lakes and streams and contributes to damage
of trees at high elevations (for example, red spruce trees above 2,000 feet)
and many sensitive forest soils. In addition, acid rain accelerates the decay of
building materials and paints, including irreplaceable buildings, statues, and
sculptures that are part of a nation's cultural heritage. Prior to falling to the
Earth, SO
2
and NO
x
gases and their particulate matter derivatives, sulfates
and nitrates, contribute to visibility degradation and harm human health.
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