The best indicator for determining the general level of air pollution in an urban area is

(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,