The 13-page report concludes that diesel vehicles over 10 years of age form only seven per cent of the city's total car fleet. Also, their removal will lead to a mere one per cent reduction in Delhi's PM 2.5 (extremely fine particles that can lodge deep inside lungs) air pollution load. The Ministry of Road Transport and Highways (MoRTH) submitted this to the green court late last month to press for reversal of NGT's order to ban all diesel vehicles over 10 years of age in the Capital.

Public transport

The NGT bench hearing the ongoing air pollution matter, however, ticked off the ministry on Monday saying, "Why has the report taken into account only private vehicles? Why hasn't it considered interstate diesel trucks and public transport? You have placed 100 pages before us without any data and analysis… just because you are IIT does not mean you know everything," Justice Swatanter Kumar had said.

One of the authors of the paper 'Understanding Role of Transport in PM 2.5 Emissions in Delhi', professor Dinesh Mohan, on Tuesday said, "We are not the only ones stating what we have. The government-appointed Mashelkar Committee Auto Fuel Policy Report itself says the number of cars in Delhi is exaggerated. The real number is 60-70 per cent of that on government record".

"The Central Pollution Control Board data saying 60 per cent of air pollution in Delhi is caused by vehicles over 10 years, which NGT is relying on, goes back to 2010. Also, the study was not done with the most modern scientific methods available. Even a report done by some scientists from the University of Birmingham, by chemical analysing Delhi's air samples, say that the overall contribution of traffic to pollution in Delhi is 16.2-18.7 per cent. This was in November 2014," professor Mohan said.

Anumita Roychowdhury of the Air Pollution and Clean Transportation programme, Centre for Science and Environment, however, requested for a different perspective on this. She said, "One must not see this through the lens of one or 60 per cent. Burning of diesel produces a toxic cocktail of nitrogen oxides and volatile organic compounds. This is a class I carcinogen".

"Also, people have a direct exposure to vehicular emissions as this source of pollution is in our immediate breathing zone. Older cars adhere to old emission standards and our current 'Pollution Under Check' norms are extremely lax," Roychowdhury said.

A senior government scientist, who did not wish to be named, said, "It is strange how they arrived at the one per cent contribution of 10-year-old diesel vehicles to pollution figure. The only two known sources of Particulate Matter 2.5 are 'vehicles' and 'high temperature combustion'. There are hardly any air pollution-causing industries in Delhi. Those from other states don't always lead to pollution here cause of varying wind direction."