Ground level Ozone, CO, oxides of Nitrogen and oxides of Sulphur are all gaseous in nature and comprise the majority of criteria pollutants the name assigned to the group of most common air pollutants. Ground level ozone is not emitted directly into the air, but is produced by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC) in the presence of sunlight. NOx and VOC themselves come into the atmosphere through emissions from industrial facilities and electric utilities, motor vehicle exhaust, gasoline vapours, and chemical solvents etc.