Explain pollution caused by automobiles and how use of catalytic converter in them reduces the pollution ?

Explanation

Automobiles are main cause of atmospheric pollution in metro cities.
Proper maintenance of automobiles along with use of lead-free petrol or diesel can reduce the pollutants they emit.
Catalytic converters contain platinum-palladium and rhodium as the catalyst, are fitted into automobiles for reducing emission of poisonous gases.
 As the exhaust passes through the catalytic converter, unburnt hydrocarbons are converted into carbon dioxide and water and carbon monoxide and nitric oxide are changed to carbon dioxide and nitrogen gas.
The vehicles fitted with catalytic converter should use unleaded petrol because lead in the petrol inactivates the catalyst.
In Delhi, entire fleet of public transport was converted to Compressed Natural Gas (CNG) mode to reduce the fast increasing pollution level of metro.