Air pollutants are added in the atmosphere from different sources. These include:
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Natural activities:
Natural decomposition and fires, cyclones, volcanoes, storms produce dust particulates and different types of gases.
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Combustion of fossil fuel:
> Burning of coal produces smoke, SO2 and hydrocarbons.
> Combustion of petroleum, diesel and oils produce CO, CO2, smoke, carbon particles, leaded gas and hydrocarbons.
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Industries and factories:
Industries are the major sources of air pollutants. They produce smoke, carbon particles, fumes, toxic gases and metallic particles such as Mercury, Lead and Cadmium.
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Agricultural sources:
Agricultural activities release spores, pollen grains, biocides, hydrocarbons and organic phosphates in the atmospheric air.
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Automobiles:
Various transportation system and vehicles produce dust, smoke and noise.
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Construction and demolition:
Construction of roads, buildings add dust particles of cement and asbestos.
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Nuclear activities:
Nuclear tests, atomic explosions and atomic reactors produce radiations, heat, noise, and harmful gases.
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Other sources:
Mists, Fog, Smog, Chlorofluorocarbons (CFCs) are added from different sources. H2S is produced by decomposition of organic wastes.
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Secondary air pollutants:
Smoke, dust particles and different gases and different gases are primary air pollutants. These are produced from direct sources. Primary pollutants react photo-chemically with the contents of air and produce secondary air pollutants:
eg. Acid rain, ozone, Peroxyacetyl nitrate (PAN), Fog, and smog, etc.