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.
(b) Revolution in automobile industry
(d) Nuclear explosion
(e) Over exploitation of natural resources.