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| Air Pollution |
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| Air is an important natural resource providing the basis of life on earth. Entire biosphere depends on air. Air in the atmosphere provides oxygen to plants and animals, by virtue of which they are able to live. |
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| The composition of air (78% N, 21% O, 0.03% CO2) is necessary to be maintained for the continuance of life on earth. Impairment of composition of air directly affects the living of plants and animals - as the life process would be curtailed in case of reduction in oxygen content in air. |
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| Polluting such a natural resource by various human activities will substantially change the composition of air. This may lead to many short term and long term implications on the life of plants and animals. Besides the change in composition, the pollution may directly add some poisonous and harmful gases - which may cause series of health complications. |
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| Based on the possible reasons, air pollution could be classified into |
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 Accidental air pollution |
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 Industrial air pollution |
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 Transport related air pollution |
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 Dwelling related air pollution |
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| Accidental air pollution is further classified into: |
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| Air pollution |
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 by forest fires |
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 by accidents to petroleum mass transport vehicles |
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 by leakage, blasts in industries |
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| Industrial air pollution can be |
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| Pollution |
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 from thermal power plants |
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 due to chemical fertilizers, food, pesticide and pharmaceutical industries |
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 due to cement, steel, paper, sugar industries |
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 due to textile and textile related industries |
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 due to petroleum and other industries |
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 due to atomic units |
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| Transport related air pollution can be |
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| Pollution |
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 due to all types of terrestrial transport system |
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 due to urban transport system |
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 due to other modes of transport |
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| Dwelling related air pollution can be |
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| Pollution |
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 due to use of aerosols |
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 due to high density of population |
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 due to waste disposal system |
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| Out of them, major contribution of air pollutants is from industrial pollution and transport related pollution - because industrial activity and transport are continuously operative. Industrial growth and growth in transport sector are regarded as important components of growth of national economy itself. Hence, these two continuously operating and growing sectors, contribute pollutants at a growing rate. |
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| Air pollution due to accidents is occasional. But they may be dangerous to emit large quantity of pollutant at a time. |
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| Dwelling related pollution is more correlated to wide spread use of advanced technologies like computers, refrigerators, air conditioners etc., as well as mis-handling or no-handling of waste disposal systems in urban agglomeration. A significant contribution is also made by natural respiration of thickly populated urban population. |
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| Formation of photochemical smog |
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| When pollutants like hydrocarbons and nitrogen oxides combine in the presence of sunlight, smog is formed. This is a mixture of gases and since it is formed by photochemical reactions, it is called the photochemical smog. The word 'smog' is derived from the two words - smoke and fog. |
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| It forms a yellowish brown haze especially during winter and hampers visibility. It also is a cause of many respiratory disorders and allergies as it contains polluting gases. |
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| Photochemical smog is mainly composed of ozone (O3), peroxyacetyl nitrate (PAN) and NOx. It is also known as brown air where solar radiation is intense. In seasons of lesser solar radiation or areas, smog formation is incomplete and the air is referred to as grey air. |
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| A simplified set of photochemical reactions involved in smog formation is as follows: |
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| Reactions occuring inside engine: |
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| Reactions occuring in atomsphere: |
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| Smog ozone may damage plant as well as animal life. Several species of plants are very susceptible to PAN in smog. PAN damages choloroplasts, which results in reduction of photosynthetic effeciency and growth of plants. |
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