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Environmental Chemistry
Is an important section in chemistry from the Civil Service
Examination point of view.
Some basic terms and explanations
Smog
It is a mixture of smoke, dust particles and small drops of fog.
Small drops of these smog contains poisonous gases produced by
burning of fuels in homes, factories and automobiles.
a) Chemical smog
Smog
b) Photochemical smog
a)
Chemical smog
Formed by the combination of smoke dust and fog containing
sulphur dioxide from polluted air.
b)
Photochemical Smog
Formed by the combination of
smoke, dust and fog with an air pollutant in the atmosphere as a
result of photochemical reaction. Photochemical oxidant will be
in high concentration in it. Develops in areas where atmosphere
contains large quantity of automobile exhausts, stagnant air and
intense sunlight.
Entire series of
process can be summarized as.
a) automobiles
emit carbon monoxide, hydrocarbons and oxides of nitrogen. When
sufficient sunlight is absent NO (Nitrogen Monoxide) reacts with
O2 to form NO2 (yellow brown gas.)
b) During sunrise, ultraviolet rays of sunlight convert NO2
back to NO and O (highly reactive Oxygen)
This reactive O combine with O2 in
air to form ozone (O3)
Ozone reacts with NO to form NO2 + O2
NO2 again absorbs U.V radiation and converts to NO +
O,
and the process go on cycling
The reactive oxygen combines with hydrocarbons also,
and
produces many undesirable compounds also.
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