Air pollution has become one of the serious environmental problems of today. Atmosphere mostly consists of gases such as nitrogen (78.08%), oxygen (20.94%), argon (0.93%) and carbon dioxide (0.035%). By maintaining a definite proportion, these gases keep the atmospheric temperature in balance. When any of these gases increases substantially, or if other solid, liquid or gaseous substances are added to the atmosphere, it disturbs the atmospheric balance which results in air pollution. Such pollution cause harm to biotic and abiotic elements.
Air pollution is caused by:
(i) Natural factors:
(a) Volcanic eruption: Air is polluted by the smoke, ashes and gases that come out in a volcanic eruption. e.g. 15-20 million tonnes of sulphur dioxide (SO₂) was emitted in the eruption of Mount Pinatubo in Philippines.
(b) Forest fire: In many parts of the earth, forest fires contribute largely to polluting the air.
(ii) Human factors:
(a) Industrialisation and urbanisation.
(b) Increase in vehicular traffic and natural explosions.
(c) Increased use of fossil fuels.
All these human activities have led to the addition of harmful gases like carbon monoxide, nitrous oxide, hydrocarbons, sulphur dioxide, etc. to the air, leading to its pollution.