There are two main sources of pollution:

(1). Natural Sources:

            (a) Volcanic ash

            (b) Marsh gas (CH4) released from decay of organic matter.

            (c) Dust from dust storm.

            (d) Pollengrains, spors, bacteria, cysts etc.

(2). Anthropogenic sources:

Man has aggravated the problem of pollution by his innumerable activities like.

            (a) Industrialization

            (b) Revolution in automobile industry

            (c) Deforestation

            (d) Nuclear explosion

            (e) Over exploitation of natural resources.