This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Epidemiology, Subject name: Social & Preventive Medicine
Most important indicator of air pollution is: 
Select and explain. 
A. SO2, B. CO2, C. CO2, D. N2O
A: SO2
Answer: A: SO2 
Explanation: Ans. a.SO2 Chemical indicator of air pollution:Sulfur Dioxide: Best indicator of Air Pollution.Smoke or soiling index: Air strain in a filter paper measured through photoelectric meter.Grit and dust measurementAir pollution indexSoiling indexCoefficient of hazeBiological indicator of air pollution: Lichens