1 What causes acid deposition?
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-Acid deposition, commonly called acid rain, is caused
by emissions of sulphur dioxide and nitrogen oxides.
Although natural sources of sulphur oxides and nitrogen
oxides do exist, more than 90% of the sulphur and 95%
of the nitrogen emissions occurring in eastern North
America are of human origin. These primary air pollutants
arise from the use of coal in the production of electricity,
from base-metal smelting, and from fuel combustion in
vehicles. Once released into the atmosphere, they can
be converted chemically into such secondary pollutants
as nitric acid and sulphuric acid, both of which dissolve
easily in water. The resulting acidic water droplets
can be carried long distances by prevailing winds, returning
to Earth as acid rain, snow, or fog.
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2 Is acid deposition always wet?
-No. The acids can be transformed
chemically into sulphur dioxide gas or into sulphur and nitrogen
salts. In this form they are deposited 'dry', causing the same
damage as when they land dissolved in rain or snow. In this
form they can also do internal damage to plants as they are
taken up from the soil.
3 Is natural
precipitation acidic?
-Yes.
Water solutions vary in their degree of acidity. If pure water
is defined as neutral, baking soda solutions are basic (alkaline)
and household ammonia is very basic (very alkaline). On the
other side of this scale, there are ascending degrees of acidity;
milk is slightly acidic, tomato juice is slightly more acidic,
vinegar is mediumly acidic, lemon juice is still more acidic,
and battery acid is extremely acidic.
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How does acid deposition affect human health?
-We
eat food, drink water, and breathe air that has come in contact
with acid deposition. Canadian and U.S. studies indicate that
there is a link between this pollution and respiratory problems
in sensitive populations such as children and asthmatics. Acid
deposition can increase the levels of toxic metals such as aluminum,
copper, and mercury in untreated drinking water supplies.
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How does acid deposition affect aquatic ecosystems?
-The
interactions between living organisms and the chemistry of
their aquatic habitats are extremely complex. If the number
of one species or group of species changes in response to
acidification, then the ecosystem of the entire water body
is likely to be affected through the predator-prey relationships
of the food web. At first, the effects of acid deposition
may be almost imperceptible, but as acidity increases, more
and more species of plants and animals decline or disappear.
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How does acid deposition affect terrestrial plant life?
-Both
natural vegetation and crops can be affected:
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It can alter the protective waxy surface of leaves, lowering
disease resistance.
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It may inhibit plant germination and reproduction.
- It accelerates soil weathering
and removal of nutrients.
- It makes some toxic elements,
such as aluminum, more soluble. High aluminum concentrations
in soil can prevent the uptake and use of nutrients by plants.
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