(1) Air Pollution: Air is mainly a mixture of various gases such as oxygen, carbon
dioxide, nitrogen. These are present in a particular ratio. Whenever there is
any imbalance in the ratio of these gases, air pollution is caused. The sources
of air pollution can be grouped as under
(i) Natural; such
as, forest fires, ash from smoking volcanoes, dust storm and decay of organic
matters.
(ii) Man-made due to
population explosion, deforestation, urbanization and industrializations.
Certain activities of human beings release several pollutants in
air, such as carbon monoxide (CO), sulfur dioxide (SO2), hydrocarbons (HC),
oxides of nitrogen (NOx), lead, arsenic, asbestos, radioactive matter, and
dust. The major threat comes from burning of fossil fuels, such as coal and petroleum
products. Thermal power plants, automobiles and industries are major sources of
air pollution as well. Due to progress in atomic energy sector, there has been
an increase in radioactivity in the atmosphere. Mining activity adds to air
pollution in the form of particulate matter. Progress in agriculture due to use
of fertilizers and pesticides has also contributed towards air pollution.
Indiscriminate cutting of trees and clearing of forests has led to increase in
the amount of carbon dioxide in atmosphere. Global warming is a consequence of
green house effect caused by increased level of carbon dioxide (CO2). Ozone
(O3) depletion has resulted in UV radiation striking our earth.
|
The gaseous composition of unpolluted air |
|
|
The
Gases
|
Parts
per million (vol)
|
|
Nitrogen
|
756,500
|
|
Oxygen
|
202,900
|
|
Water
|
31,200
|
|
Argon
|
9,000
|
|
Carbon Dioxide
|
305
|
|
Neon
|
17.4
|
|
Helium
|
5.0
|
|
Methane
|
0.97-1.16
|
|
Krypton
|
0.97
|
|
Nitrous oxide
|
0.49
|
|
Hydrogen
|
0.49
|
|
Xenon
|
0.08
|
|
Organic Postulates
|
ca.0.02
|
Harmful Effects of air
pollution –
(a) It affects respiratory system of living organisms and causes
bronchitis, asthma, lung cancer, pneumonia etc. Carbon monoxide (CO) emitted
from motor vehicles and cigarette smoke affects the central nervous system.
(b) Due to depletion of ozone layer, UV radiation reaches the
earth. UV radiation causes skin cancer, damage to eyes and immune system.
(c) Acid rain is also a result of air pollution. This is caused
by presence of oxides of nitrogen and sulfur in the air. These oxides dissolve
in rain water to form nitric acid and sulfuric acid respectively. Various
monuments, buildings, and statues are damaged due to corrosion by acid present
in the rain. The soil also becomes acidic. The cumulative effect is the gradual
degradation of soil and a decline in forest and agricultural productivity.
(d) The green house gases, such as carbon dioxide (CO2) and
methane (CH4) trap the heat radiated from earth. This leads to an increase in
earth’s temperature.
(e) Some toxic metals and pesticides also cause air pollution.