Air pollution is the introduction of biological materials or chemicals into the air that can cause harm to humans and other living organism.
There are different forms of pollutants such as liquid droplets, gaseous forms or solid particles. These pollutants could be man-made or natural.
Pollutants can be of two types: primary and secondary. Generally, primary pollutants are matters released from a process, such as ash released by a volcanic eruption, carbon monoxide gas released from a vehicle exhaust or emission of sulfur dioxide from factories.
Pollutants which are not emitted directly are called secondary pollutants. They are formed in the air due to the reaction or interaction of primary pollutants with each other. Ground level ozone is one such secondary pollutant and it makes up for the photochemical smog.
Two major primary pollutants produced by human activity are:
Sulfur oxides: is a chemical compound with the formula of SO₂. Industrial processes and volcanoes result in the production of SO₂. Sulfur compounds are found in petroleum and coal and their combustion generates sulfur dioxide. Further oxidation of SO₂ forms H₂SO₄ or acid rain when it is in the presence of a catalyst such as NO₂.
Carbon dioxide: the gas has no color or odor but is very harmful. A major source of this poisonous gas is vehicle exhausts.