Sunita Narain in the city on Thursday. (Rashbehari Das)

A diesel and katatel combo is deadly for Calcutta, according to researchers studying fuel consumption in various cities.

“Two-stroke autos running on adulterated petrol (katatel) pump noxious pollutants into your bodies and diesel combustion completes the pollution cycle. It’s a combination that is not only foul but also fatal,” Sunita Narain, the director of the Delhi-based Centre for Science and Environment, told Metro on Thursday.

Narain, whose organisation had spearheaded the clean-air crusade that converted the capital into a CNG city, revealed during a conference earlier in the day that Calcutta was the “world capital” of diesel with nearly 99 per cent of the city’s commercial fleet dependent on the fuel.

“Depending on the season, diesel-fuel combustion contributes as much as 61 per cent to the presence of fine respirable particulate matter (that causes maximum damage to lungs) in the Calcutta air,” she said.

One diesel car emits as much nitrogen oxide as three to five petrol cars . The older the vehicle, the higher its emission.

The high court has ordered all commercial vehicles that are 15 years and older to be phased out by March 31. “Going by the go-slow in the two-stroke auto phaseout (the original deadline was December 31), this is a process that doesn’t look likely to be completed anytime soon,” said Subhash Dutta, whose petition had led the court to ban two-stroke autos.

The government had promised the court during the last hearing on January 9 that it would replace 3,000 two-stroke autos with four-stroke ones that run on LPG every month. But barely 250 autos have been replaced in the past five weeks, officials of Bajaj Auto Ltd said.

An auto union official claimed that the authorities were “sitting” on their applications. Environment secretary M.L. Meena blamed the banks picked to finance auto purchases for the delay.

Narain said quoting a study that Calcutta had the best public transport-private car ratio among major cities — Mumbai, Delhi, Chennai, Ahmedabad, Pune and Bangalore.

“But it needs to leapfrog to solutions: phase out two-stroke autos and old commercial vehicles quickly and simultaneously make the transition to public transport that uses clean fuel,” Narain said.