Pollution is increasing, but why has the government targeted diesel vehicles only?

Why is the government cracking down on diesel specifically?

Around the world, diesel has been seen in recent years as being more environmentally hazardous than petrol. This is why there are tighter restrictions on diesel vehicles in India too.

The National Green Tribunal (NGT) had ordered in 2015 that diesel vehicles more than 10 years old would not be allowed to ply in the Delhi-NCR region; this window was kept at 15 years for petrol vehicles. A challenge to the decision was dismissed by the Supreme Court, and the NGT subsequently rejected appeals for a review.

But wasn’t diesel the preferred fuel even in environment-conscious Europe until recently?

Yes. Diesel was promoted as a green-friendly auto fuel as part of the European Union’s response to the Kyoto Protocol (1997) to reduce carbon-dioxide emissions. While diesel as a fuel contains a little more carbon per litre than petrol, diesel engines are more “lean-burn”, which means they use a smaller amount of fuel to produce the same level of performance as a petrol engine.

What is the problem with diesel engines, then?

The issue is not with CO2 emissions specifically. It is with some other toxic emissions that are harmful to human beings, as well as emission of soot. This is where diesel is worse off than petrol.

When air is heated in an automobile engine, nitrogen oxides (NOx) are produced — these include nitrogen dioxide (NO2) which is toxic; nitrous oxide (N2O), which is a greenhouse gas; and nitric oxide (NO), which reacts with oxygen to form the harmful NO2. Nitric oxide on its own also increases the risk of respiratory problems in the long run.

In a petrol engine, a three-way catalytic converter reduces these emissions, ensuring that the NOx emissions are about 30 per cent lower than they would be in a diesel engine on average.

While modern diesel cars are fitted with particulate filters that take care of NOx emissions (reducing them by 90%, according to some estimates), diesel engines also emit fine particulate matter (PM) in their tailpipe emissions. This is essentially soot, the finest particles of which can be embedded deep in the lungs, and they can cause heart and respiratory problems in the longer term. PM has also been linked to cancer.

And is there a problem specifically with India?

What is also to be noted is that heavier vehicles like trucks and buses, which in India are usually likely to be less well maintained and therefore, more polluting, mostly run on diesel. Also, many trucks are old, and therefore, use older, dirtier technology. Tighter restrictions on diesel in that sense translate into tighter restrictions on these commercial vehicles.

Also, before the decontrol of automobile fuel prices began in late 2014, the price of a litre of diesel was significantly lower than that of the price of petrol — a huge Rs 25 at its peak — which pushed very large numbers of people to buy diesel cars.

In 2012-13, diesel cars accounted for 48% of passenger vehicle sales in the country. Following the decontrol, as the prices of the two fuels came much closer, diesel cars accounted for just about 22% of overall passenger vehicle sales in 2018-19, less than half the share that they had five years previously.