A pollutant may be defined as anything or non-living or any physical agent (heat, sound etc.) that in its excess makes any part of the environment undesirable or contaminated. Pollutants may either man made or natural.
Types of pollutants
A) On the basis of pollutant origin
i) Natural pollutants (the pollutants which come out from natural sources as dispersal of pollens, soil erosion, volcanic eruption etc
ii) Manmade pollutants (the pollutants which are produced by human activities)
B) On the basis of pollutant genesis
i) Primary pollutants (the pollutants which directly emitted from a process, such as ash from a volcanic, the carbon monoxide gas from motor vehicle exhaust)
ii) Secondary pollutants (the pollutants that are not emitted directly but form in the air when primary pollutants react or interact e.g. ground level ozone)
C) On the basis of chemical composition
i) Gaseous pollutants
Oxides of nitrogen (NO, N02), SO,, H2S, CO, halogens
ii) Solid waste
iii) Complex organic pollutants
Benzene, benzapyrene, acetic acid, ether etc
iv) Heavy metals
Mercury, Lead, cadmium, nickel, tin, arsenic etc.
v) Fluoride compounds
vi) Deposited matter Smoke, tar, dust, fly ash etc.
vii) Photochemical oxidants
Ozone, PAN, Pb2N, aldehydes, ethylene etc
Herbicides, fungicides, nematocides, insecticides, rodenticides and other biocides
x) Radioactive waste
A contaminant is something, which causes a deviation from normal composition of an environment. Contaminants are not pollutants unless they have some detrimental effects. A contaminant does not occur in nature but get introduced by human activity into the atmosphere affecting its composition.