Automobiles burn petroleum inefficiently causing $80\%$ of air pollution and $75\%$ of noise pollution in urban areas. They release hydrocarbons $(13.7\%)$, carbon monoxide $(77.2\%)$, nitrogen oxides $(7.7\%)$, sulphur oxides, ammonia, aldehydes and lead (90% of total lead poisoning). Lead is present in petroleum in the form of $Pb(CH_3)_4$ and $Pb(C_2H_5)_4$ as antiknock agent.