The government sought stay on order banning plying of over 10-year-old diesel vehicles in Delhi—NCR by quoting a study by IIT Delhi, and both were hauled up by the National Green Tribunal (NGT).  It directed that they come back with a thorough explanation from IIT Delhi on why they think the ban will not be effective. The NGT stayed the ban till May 25.

The tribunal was angry during a hearing on Monday as it felt that the scientists from IIT and the ministry of road transport had not prepared a well reasoned report on how much air pollution do more than ten year old diesel vehicles contribute.

The green tribunal wanted the ministry to submit its views on capping total number of vehicles, scrapping of old vehicles, car pooling and incentives to those who want to dispose of their old vehicles.

The ministry was against the ban as it claimed that more than ten year old diesel vehicles contribute to less than 1% of PM 2.5 (fine, respirable pollution particles) emissions in the city. Their argument is based on a study by Dinesh Mohan and other IIT scientists. The ministry had argued that only 7% of the vehicles in the capital are more than 10 years old.

“What is the basis of this report? IIT has no business to comment on this. This report is not comprehensive enough. They have not taken samples from any place. IIT could have done a better job. You have placed 100 pages without conducting any study. Merely because you are IIT you can’t be always right,” the bench said.

The NGT bench said they expected much better from IIT Delhi in terms of both research and analysis of the problem.  For example, the study said PM 2.5 levels in RK Puram were on Sundays or holidays despite traffic being very low. The NGT bench asked what is IIT Delhi's explanation on this? "Why are the levels high? Are they because of trucks and commercial vehicles plying at night?" one of them asked.

The NGT bench also said that the IIT study only refers to private vehicles but what about contribution from diesel commercial and heavy vehicles?

“Don’t try to tell us our order is wrong. The whole IIT report is tilted towards proving that the ban order is bad. There has to be proper reasoning to what you are saying,” the bench added.

The bench also referred to a Central Pollution Control Board (CPCB) study which found that old vehicles are responsible for 60% of air pollution from vehicles despite being very small in number. "Merely because you are IIT doesn't mean you can do this? There has to be proper reasoning to what you are saying."

The ministry is willing to ban more than 15 year old diesel vehicles, which has been ordered by the supreme court earlier.