Explanation

The major cause of air pollution in big cities is automobile exhaust. In all major metropolitan cities, vehicular exhaust accounts for 70% of all $CO\$(carbon monoxides), 50% of all hydrocarbons, 30-40% of all oxides and 30 % of all SPM. The vehicular exhaust produces many air pollutants including unburnt hydrocarbons, $CO,NO_{x}$ and lead oxides along with traces of aldehydes, esters, ethers, peroxides and ketones.