This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Miscellaneous, Subject name: Social & Preventive Medicine
The best indicator for determining the general level of air pollution in an urban area is 
Select and explain. 
A. Sulphur dioxide, B. Carbon dioxide, C. Hydrogen, D. Nitrogen
A: Sulphur dioxide
Answer: A: Sulphur dioxide 
Explanation: (A) Sulphur dioxide > Best indicators of air pollution are sulphur dioxide, smoke, suspended particles.# Monitoring of air pollution> Best indicators of air pollution are sulphur dioxide, smoke and suspended particles> These are monitored on a daily basis over several sites. The results are then collected by a central agency.> Sulphur dioxide: This gas is a major contaminant in many urban and industrial areas. Its concentration is estimated in all air pollution surveys,