"We will not order any coercive measures today," the NGT bench said, directing all state governments to file affidavits within three weeks with details of their two most polluted cities, including the total number of vehicles along with a break-up of diesel, petrol, heavy and light vehicles. The bench has also sought details on pollution caused by industry or mining (if any), and the population of each of the two cities. "Let that data come and then we will hear different parties and decide accordingly," the bench said.

The Centre and auto manufacturers, meanwhile, argued for a new source apportionment study to arrive at the pollution contribution of large diesel cars. In an affidavit, they questioned the rationale behind singling out diesel cars when petrol also caused emissions of greenhouse gases such as CO2.

The ministry of heavy industries and public enterprises, represented by additional solicitor general (ASG) Pinky Anand and advocate BalenduShekhar, and the Society of Indian Automobile Manufacturers (SIAM), represented by Abhishek Singhvi, argued that diesel was not the only source of air pollution. "The government has a plan for air pollution which has short, medium and long term goals," Anand said, adding that a ban on diesel vehicles will "severely impact" the Make in India initiative as well as FDI.

Among the measures listed by the Centre in its affidavit ( see graphic) on pollution control is the formulation of a policy to scrap older vehicles, which will enable their replacement with "environment-friendly" vehicles.