This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
All are indicators for air pollution , except ? 
Select and explain. 
A. CO2, B. SO2, C. Soiling Index, D. Smoke index
A: CO2
Answer: A: CO2 
Explanation: 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