Air pollutants are added in the atmosphere from different sources. These include:
Natural decomposition and fires, cyclones, volcanoes, storms produce dust particulates and different types of gases.
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.
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.
Agricultural activities release spores, pollen grains, biocides, hydrocarbons and organic phosphates in the atmospheric air.
Various transportation system and vehicles produce dust, smoke and noise.
Construction and demolition:
Construction of roads, buildings add dust particles of cement and asbestos.
Nuclear tests, atomic explosions and atomic reactors produce radiations, heat, noise, and harmful gases.
Mists, Fog, Smog, Chlorofluorocarbons (CFCs) are added from different sources. H2S is produced by decomposition of organic wastes.
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.