Are big cars cleaner? Not yet in India


Do big cars really cause less pollution than small ones, as Attorney General Mukul Rohatgi has claimed in the Supreme Court? Fact is there is no way to ascertain that, simply because car manufacturers do not share the emissions profile of their vehicles.

Moreover, technology treatments that allow certain big cars to be cleaner than their smaller compatriots aren’t available here because they require ultra-low-sulphur diesel that isn’t yet commercially available in the country.

On Monday, the Centre claimed that big and high-end diesel cars pollute less than small cars while challenging the court’s blanket ban on fresh registration of diesel luxury cars and SUVs with over 2000 CC engine capacity in Delhi.

“Just because a car is big and powerful, it does not mean it is more polluting. Besides, the more expensive a car is, say Rs. 75 lakh or Rs. 1.5 crore, the better equipped it is against pollution,” the Centre, represented by Attorney General Mukul Rohatgi, told the court.

An analyst at the Belgium-based Transport and Environment told The Hindu that a big diesel car could have reduced nitrous oxide emissions than a small car if it employed specific exhaust treatment technologies. Cars equipped with Selective Catalytic Reduction (SCR) module cost about €100 (Rs. 7,500) more than those with Exhaust Gas Recovery (EGR) and nitrogen trap, said Greg Archer in an email. All new cars in Europe were equipped with filters, he said.

Trouble is that SCR, which is scheduled to become mandatory for the forthcoming Euro 6 norms in 2020, and even EGR are presumed to be effective only if they use diesel that has sulphur content less than 50 parts per million. Oil companies in India have yet to put in infrastructure to produce such diesel.

“The Attorney-General wasn’t speaking literally, but trying to remove the misconception that bigger vehicles necessarily pollute more,” said a source closely associated with auto emissions policy and present at the court hearing.

Norms in India

Diesel engines, now globally castigated for being a source of nitrous oxides and particulate matter and believed to aggravate several lung diseases, can vary in the quantity of particulate matter they emit.

As of today, diesel engine cars in India are only required to ensure that they emit no more than 0.025 gm/km of particulate matter if they are “small” and 0.06 gm/km if they are “big” or 2000 cc-and-above and only if they are registered in the 13 Indian cities bound by the Bharat Stage-4 norms.

The same cars are allowed to emit roughly 10 times more nitrous oxide emissions, again depending on the weight class. This underlines the paradox of pollution by diesel engines. The way a diesel engine burns its fuel is more efficient compared to a petrol engine.

While this could mean less particulate matter, it correspondingly raises nitrous oxide levels. Conversely, trying to rein in nitrous oxides will compromise fuel-use efficiency and increase particulate matter emissions.

Volkswagen, Mercedes and Toyota cars are equipped with particulate filters abroad. But they are not available in their Indian versions.

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