All are indicators for air pollution , except ?

Ans. is 'a' i.e., CO2 o Carbon dioxide is also an air pollutant, but it is not used as an air pollution indicator. o Park writes -- "It is not commonly regarded as an air pollutant although man generates enormous amount of it in combustion process using coal, oil and gas. Carbondioxide is a natural constituent of the air It does not take pa in any significant chemical reactions with other substances in the air". o The best indicators of air pollution are Sulphur dioxide Smoke (soiling index) Suspended paicles