Natural sources:

(a) Volcanic eruption: Releasing poisonous gases like SO₂, H₂S, CO etc.

(b) Forest fires: In the areas of tropical region throughout the year forest fire is a common feature. very large quantities of smoke and particulate matter are released during their breakout.

(c) Natural organic and inorganic decays or vegetative decays. methane gas, carbon dioxide are released into the air

(d) Dust: Dust is always present in the atmosphere in varying amounts.

(e) Pollen grains of flowers: Pollution is also caused by the production of pollens in the spring season.

Pollens or aeroallergens enter the atmosphere form weeds, grasses and trees. They are mainly responsible for causing allergy.

(f) Fungal spores: Micro-organisms such as algae, fungi, bacteria, yeasta, rusts spores etc are present as variable particles in the atmosphere.

(g) Radioactive materials: The radioactive minerals present in the earth crust and action of cosmic rays from outer space on gaseous constituents of the atmosphere are mainly responsible for radioactivity of the atmosphere.

The term pollution have derived from latin word pollute. Pollute means make dirty. Thus pollution means a change in the physical, chemical and biological aspects of environment. This pollution is very harmful to human life and all other living beings.

Different types of pollution:

(i) According to environment: When different segments of the environment are affected by pollution, they may be categorised as

(a) Air pollution.

(b) Water pollution.

(c) Soil pollution.

(ii) According to pollutant: pollution caused by pollutants may be of different types such as

(a) Thermal pollution.

(b) Noise pollution.

(c) Radioactive pollution.

(d) Solid waste pollution.

(e) Oil pollution.

(f) Industrial pollution.

(g) Marine pollution.