The substances or agents causing air pollution by their concentration are known as air pollutants.
The air pollutants are of two types:
a) Particulate air pollutants:
Carbon particles, metallic particles, dust, tars, solid oxides nitrates and sulphates are particulate types of air pollutants.
b) Gaseous air pollutants:
Oxides of carbon (CO, CO2), Oxides of sulphur (SO2, SO3), Oxides of nitrogen (NO, NO2, N2O), H2S, and hydrocarbons are the gaseous air pollutants.
Smoke, Fumes, Heat radiations are also air pollutants.