An air pollutant is a substance in the air that can have adverse effects on human beings and other living things. The substance may be solid particles, liquid droplets or gases. It can be of natural origin or man-made.
The air pollutants are classified into two main types:
1. Primary Pollutants
2. Secondary Pollutants
1. Primary Pollutants
These substances are emitted directly into the atmosphere. Carbon oxides, sulfur oxides and nitrogen oxides emitted by automobiles are examples of primary pollutants.
2. Secondary Pollutants
These substances are not emitted directly into the atmosphere, but are formed by various physical processes in the atmosphere. Ground level ozone and peroxyacetyl nitrate (PAN) are examples of secondary pollutants.
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