It was barely three weeks ago that the Supreme Court banned registration of all diesel vehicles over 2000cc for three months in Delhi. The companies worst hit were Mahindra & Mahindra, Mercedes-Benz and Toyota Kirloskar Motor.

The Court will now hear their appeals seeking a modification to the ban on Tuesday. It is also scheduled to impose a pollution tax levy on diesel vehicles with engine capacities of under 2000cc on Tuesday. This could then affect a host of models from the stables of Hyundai, Ford, Renault, Nissan, Tata Motors and Maruti.

Clearly, these are not the best of times for diesel automakers. In their view, fine particulate matter (PM) in the Capital begins rising in winter thanks to weather conditions coupled with emissions released during festivals, burning of biomass and from buses. Typically, the air also begins clearing up from January and the PM levels continue at this level for months thereafter. They end up falling in peak summer between May and September.

To that extent, automakers are convinced that this pattern will be replicated in 2016 too, and should not be seen as a result of the diesel ban. In fact, insists a top industry official, PM levels have consistently fallen in these months, despite more vehicles coming on to the roads. He adds that the PM has stayed at the same levels over the last decade which clearly shows that cars are not the villains of the piece.

The industry also believes that the WHO study on diesel fumes being carcinogenic was a result of using an old diesel engine, whereas the findings have been different in the case of The Health Effects Institute, Boston. In this case, a modern diesel engine was used and did not show any indication of carcinogenic lung tumours. Carmakers say this is equally true for diesel engines used in India which, at BS V levels, are fitted with the right equipment to remove carcinogenic particles.

Even as diesel continues to face the flak, experts say petrol vehicles are end up emitting twice as much carbon monoxide. Diesel vehicles emit nearly 30 per cent carbon dioxide which, in this context, make them safer than petrol vehicles or even CNG that spews out nitrogen oxides.

Pollution report The IIT-Kanpur report on pollution showed that road dust contributes the most to PM at 38 per cent followed by vehicles at 20 per cent. Diesel generator sets and the construction industry followed with 19 per cent with domestic fuel burning contributing to 12 per cent.

Of this 20 per cent from vehicles, nearly 50 per cent comes from trucks and a third from two-wheelers. Cars make up 10 per cent, while buses, light commercial vehicles and three-wheelers account for the balance with single digit figures.

Automakers argue that in the car pie, the share of diesel vehicles is minuscule at 0.5 per cent of the total PM load. As a result, they cannot be singled out as the biggest pollutants when there are other sources, which are aggravating the foul air.

Switch to newer vehicles What then is the best way forward? The industry maintains that replacement of old vehicles is the answer where operators can be offered incentives to switch to new and cleaner BS IV vehicles. Similarly, in the transition to cleaner norms, this should be done across the country instead of a piecemeal route as has been the case so far.

Going forward, say experts, BS V norms should be introduced from 2019. There is little point jumping directly to BS VI as any technology upgrade will need a gradual process of change.

More importantly, they caution, skipping BS V and moving to BS VI in 2020 could come in the way of reducing PM from passenger cars by a year. In addition, there is no real reduction in PM emissions from cars, while moving from BS V to BS VI norms.

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