iii) Chemical industries including pesticides, fertilizers, weedicides, fungicides.
(iv) Cosmetics.
(v) Processing industries like cotton textiles, wheat flour mills, asbestos.
(vi) Welding, stone crushing, gem grinding.
Natural air pollutants include (a) pollen, spores, (b) marsh gas, (c) volcanic gases and (a) synthesis of harmful chemicals by electric storms and solar flares. The major cause of pollution in the urban areas is automobiles which inefficiently burn petroleum, releases 75% of noise and 80% of air pollutants. Concentration of industries in one area is another major cause of air pollution.