Gaseous
Air Pollutants
a) Oxides of
Sulphur:
ü Oxides
of sulphur are produced when sulphur
containing fossil fuel is burnt.
ü The
most common species sulphur dioxide, is a gas that is
poisonous to both animal and plants.
ü It has
been reported that even a low concentration of sulphur
dioxide causes respiratory diseases, e.g., asthma, bronchitis, emphysema in
human beings.
ü The
presence of particulate matter in polluted air catalyses
the oxidation of sulphur dioxide to sulphur dioxide to sulphur
trioxide.
2SO2
(g) + O2 (g) → 2SO3 (g)
ü The
reaction can also be promoted by ozone and hydrogen peroxide.
SO2
(g) + O2 (g) → SO3 (g) + O2 (g)
SO2
(g) + H2O2 (l) → H2SO4 (aq)
b) Oxides of
Nitrogen:
ü Dinitrogen
and dioxygen are the main constituents of air.
ü These
gases do not react with each other at a normal temperature.
ü NO is
oxidized to nitrate ion, NO where it serves as a fertilizer.
N2
(g) + O2 (g) → 2NO2 (g)
ü NO
reacts instantly with oxygen to give NO2.
2NO (g)
+ O2 (g) → 2NO2 (g)
ü Rate of
production of NO2 is faster when nitric oxide reacts with ozone in
the stratosphere.
NO (g)
+ O3 (g) → NO2 (g) + O2 (g)
ü The irritant red haze in the traffic and
congested places is due to oxides of nitrogen.
ü Higher concentrations of NO2
damage the leaves of plants and retard the rate of photosynthesis.
ü Nitrogen dioxide is a lung irritant that
can lead to an acute respiratory disease in children. It is toxic to living
tissues also. Nitrogen dioxide is also harmful to various textile fibres and metals.
c)
Hydrocarbons:
ü Hydrocarbons are composed of hydrogen and
carbon only and are formed by incomplete combustion of fuel used in
automobiles. Hydrocarbons are carcinogenic, i.e., they
cause cancer.
ü They harm plants by causing ageing,
breakdown of tissues and shedding of leaves, flowers and twigs.
d)
Oxides of Carbon:
ü Carbon monoxide: Carbon monoxide (CO) is one of the most
serious air pollutants.
ü It is a colourless
and odourless gas, highly poisonous to living beings
because of its ability to block the delivery of oxygen to the organs and
tissues.
ü It is produced as a result of incomplete
combustion of carbon.
ü Carbon monoxide is mainly released into the
air by automobile exhaust.
e)
Carbon
Oxide:
ü Carbon dioxide (CO2) is released
into the atmosphere by respiration, burning of fossil fuels for energy, and by
decomposition of limestone during the manufacture of cement.
ü It is also emitted during volcanic
eruptions.
ü Carbon dioxide gas is confined to troposphere
only. Normally it forms about 0.03 per cent by volume of the atmosphere.
ü The increased amount of CO2 in
the air is mainly responsible for global warming.
CO2 net gain process
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