The atmosphere of large/metropolitan cities is primarily polluted by which of the following?

Steps taken by the Government of India to control air pollution include:

Describe air pollution. How can it be controlled?

Consider the following statements about a scrubber:
$I.$ It is used to remove gases like sulphur dioxide from industrial exhaust.
$II.$ In a scrubber,the exhaust is passed through a spray of water or lime.
$III.$ Water dissolves gases and lime reacts with sulphur dioxide to form a precipitate of calcium sulphate or calcium sulphide.
Which of the statements given above are correct?

By the end of $2002$, which step was completed in Delhi to reduce vehicular pollution?

Explain the preventive measures to control pollution in Delhi.