The common gaseous pollutants are oxides of carbon (CO and CO2 ), oxides of nitrogen ( NO and NO2 ), oxides of sulphur (SO2 and SO3 ), all these together contribute 90% of the global air pollution. Out of all these, CO2 is not a pollutant. Normally, the green plants, by photosynthesis balance the CO2 and O2 ratio in the air to a great extent, but when its level increases beyond normal in atmospheric air then it contributes to global warming through enhanced green house effect.