What is pollution? Differentiate between primary air pollutants and secondary air pollutants.

Explanation

Pollution is defined as any undesirable change in physical, chemical or biological characteristics of air, land, water or soil.
The agents causing pollution are called as pollutants.
1. Depending upon unchanged or changed nature, pollutants can be primary or secondary.
(i) Primary Pollutants. Pollutants persisting in the environment in the form they are passed. into it e.g., DDT.
(ii) Secondary Pollutants. Pollutants which are formed by reaction amongst the primary pollutants. For example, `O_3` and peroxyacyl nitrates (PAN) are formed through reaction between nitrogen oxides and hydrocarbones in the presence of sunlight. Secondary pollutants are often more harmful than primary pollutants. The enhanced effect is called synergism.