Explain the preventive measures to control pollution in Delhi.

(N/A) Delhi ranked fourth among the $41$ most polluted cities in the world.
Delhi leads the country in its levels of air pollution.
Air pollution problems in Delhi became so serious that a public interest litigation $(PIL)$ was filed in the Supreme Court of India.
Supreme Court has directed the government to take,within a specified time period,appropriate measures including switching over the entire fleet of public transport,i.e.,buses,from diesel to compressed natural gas $(CNG)$.
All the buses of Delhi were converted to run on $CNG$ by the end of $2002$.
$CNG$ burns most efficiently,unlike petrol or diesel.
Very little of it is left unburnt.
$CNG$ is cheaper than petrol or diesel.
$CNG$ cannot be siphoned off by thieves and adulterated like petrol or diesel.
Other measures include:
Phasing out of old vehicles.
Use of unleaded petrol.
Use of low-sulphur petrol and diesel.
Use of catalytic converters in vehicles.