Acid rain fall-out of acids
caused by sulfur dioxide and nitrogen oxides with rainfall and thus increases
in the amount of acidity of rainwater. As pointed out above rainwater is not pure because
atmospheric carbon dioxide is dissolved in the rainwater which thus because
moderately acidic, the pH being generally 5. The water with Ph value of 7.0 is
called neutral water whereas the pH value below it makes the water alkaline.
The water becomes more injurious when the pH fall below 4.
Sulfur dioxide emitted from man
made sources in large quantities into the atmosphere combines with water to
form sulfur and sulfuric acids (H2SO4).
These acids fall on the earth's surface with rainfall and thus the fall of
highly acidic water are called acid rain. The pH of rainwater in some
localities of the USA mainly in West Virginia has gone down to 1.5 pH of
rainwater in Europe is as low as 2.4 whereas the normal range of pH of neutral water
must be 7.0.
The main sources of acid rains
are oxides of sulfur and nitrogen which are emitted from industrial
establishments and different types of vehicles. These pollution are spread in
atmosphere by wind and from acids after reacting with water in the atmosphere.
It may be pointed out that acid rains are not confined to the source areas of
the emissions of oxides of sulfur and nitrogen rather they cover much larger
areas far away from the source pollutants being in gaseous phase are carried
away and spread over larger areas through winds and clouds. For example, oxides
of sulfur and nitrogen spewed from several mills in Germany and U.K have
caused widespread acid rains in Scandinavia countries with the result most of
the lakes in Scandinavia countries have lost their biological communities and
are now biologically termed as dead lakes.
Dead lake means destruction and
death of all aquatic lives including plants and animals in lakes, ponds, and
rivers. Acid rains also affect human community adversely, though the mode of
human disease and death due to acid rains has not been properly understood as
yet. The productivity of soils is also significantly lowered because of acid
rains as increased acidity destroys mineral elements and other nutrients of the
soils.
Acid rain is not a local problem
or a problem of a particular country, rather it is an international problem
because air pollutants emitted from a particular country are carried in the
atmosphere by the winds and are spread over other countries. Thus the problem
of acid rains should be tackled at international level.
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