Combustion of fossil fuels and wood in industries, automobiles, aircrafts, railways, thermal plant kitchens etc., agricultural operations and industrial processing are major sources of air pollutions. All the pollutions sources are grouped into two main categories.

(a)   Natural;

(b)   Man-made or anthropogenic

(a)    Natural sources: it includes:

(i)     Volcanic eruptions release many poisonous gases and ash.

(ii)   Carbon monoxide from the breakdown of methane.

(iii) Forest fires.

(iv) Natural contaminates such as pollen grains, fungi, spores, cysts etc.

(v)   Dust storms.

(vi) Salt spray from oceans.

(b)     Manmade or anthropogenic sources:

(i)     Increase in population

(ii)   Deforestation

(iii) Fossil fuel combustion

(iv) Vehicular emissions

(v)   Industrialization

(vi) Use of pesticides, insecticides in agriculture

(vii)  Explosives used in wars.