NEW DELHI: Centre for Science and Environment (CSE) on Monday alleged that the Centre resorted to " selective use" of studies by IIT-Delhi to argue that vehicles were minor contributors to PM 2.5 (fine, respirable particles) levels and that banning older diesel vehicles would not help in improving the city's air quality.

The Union ministry of road transport and highways has so far submitted three scientific studies to substantiate their argument against the ban on old vehicles. Two of them are by Transportation Research and Injury Prevention Programme (TRIPP) of IIT-Delhi and another by University of Birmingham, Desert Research Institute, Reno and the Central Road Research Institute.

The ministry has also tried to argue that the transport sector's contribution to air pollution may have been overestimated by people. But

CSE said two important issues have been hidden from the NGT bench the impact of diesel fumes from vehicles in the breathing zone and the toxicity of diesel, which is graded as a carcinogen by WHO.

"While resorting to number crunching to prove that vehicles do not contribute much to ambient PM2.5 levels, the IIT-study and the affidavits are silent on health risks from direct exposure to vehicular fume, especially diesel fume that is of bigger concern. While the NGT order covers all old diesel vehicles in both private and commercial segments across the NCR, this study focuses only on old cars in Delhi to stop the NGT ban," CSE said in a statement.

It assessed the IIT-D studies that were submitted to NGT and said they could be misleading. The study states that the number of vehicles in the 11-15 years' age bracket is very small only 6% of the total fleet, which contributes 1% to PM 2.5. "The emission load from diesel vehicles that are 11-15 years' old and meet older emissions standards emit a lot more on a per vehicle basis than those that are between 1 and 10 years' old. Compared to a BS-IV car, a 15-year-old diesel car emits 7.6 times higher particulate matter and 3.4 times higher NOx," CSE added.

Emissions from one old diesel car are equal to that from four to seven new cars. "A 10-year old diesel car emits 2.4 times higher PM.

Removing old vehicles will reduce direct exposure substantially. This benefit will be much higher if the old diesel trucks are also removed or bypassed," CSE said.

CSE also pointed out that PUC norms are extremely lax for BS I and BS II diesel vehicles, which fall under NGT's ban category. Globally the smoke density norms for diesel vehicles are much tighter including in Thailand, Hong Kong, Indonesia, Malaysia, Pakistan and Singapore.

CSE's review of the PUC norms has shown that PUC tests can barely fail maximum of 6% vehicles, they said reacting to ministry's argument that NGT's ban should be fitness based.

"It is inexplicable why MoRTH has considered the estimates of only one study on the estimates of vehicles' contribution to PM 2.5. The IIT-D study fails to highlight the health risk from the direct exposure to vehicular fume that is of serious concern globally. Vehicular emissions take place within our breathing zone," the environmental think-tank said.

For example, studies by Health Effect Institute have shown that the influence of vehicular pollution is maximum up to 500 metres from roadside and more than half of Delhi's population lives within this breathing zone, the statement said.

CSE also said that IIT-D had not guided the government and NGT about the toxic risk and the fact that WHO and IARC have classified diesel exhaust as class-I carcinogen for its strong link with lung cancer.