Air pollutants can also be broadly classified into two general groups- Primary air pollutants and secondary air pollutants.
A. Primary Air Pollutants
Primary air pollutants are those emitted directly from identifiable sources.
Examples of primary air pollutants:
1) Fine particles(less than 100 μ in diameter)
2) Coarse particles (greater than 100 μ in diameter)
3) Sulphur compounds
4) Oxides of nitrogen
5) Carbon monoxide
6) Halogen compounds
7) Organic compounds
8) Radioactive compounds
B. Secondary Air Pollutants
Secondary air pollutants are those which are produced in the air by the interaction among two or more primary pollutants,or by reaction with normal atmospheric constituent, with or without photo-activation.
Examples of secondary air pollutants:
3) PAN (Peroxy acetyl nitrate)
4) Photochemical smog
5) Formation of acid mists (H2SO4) due to the reaction of sulphur dioxide and dissolved oxygen. when water droplets are present in the atmosphere