250.

Discuss measures for the control of pollution problems with special reference to the use of C.N.G.

The engine of an automobile discharges a large number of gaseous substances into the atmosphere which includes carbon monoxide, carbon dioxide, water vapours, oxides of nitrogen (NO_x), unburnt hydrocarbons and also certain compounds of lead if leaded petrol is used. Some of these compounds are highly poisonous such as compounds of lead. In order to check this, the automobiles are filled with catalytic converters to oxidise these harmful hydrocarbons to CO₂, and H₂O.

Now a days, use of C.N.G. (compressed natural gas), liquified petroleum gas (L.P.G.) and liquefied hydrogen gas (L.H.G.) have been tested in metropolitan cities. C.N.G. is mainly a mixture of methane and ethane and a small amount of propane. C.N.G. is normally found to be associated with crude petroleum. It is compressed and stored in cylinders. Its combustion is almost complete and no poisonous vapours are released in the environment. However, special types of engines have to be filled in the vehicles where C.N.G. is used. C.N.G. is quite successful in controlling air pollution.