New Delhi: Only vehicles with BS4 engines will be exempted from action if they are found running in Delhi, the Supreme Court said today. The court modified its earlier order that had banned 10-year-old diesel-run vehicles and 15-year-old petrol-run vehicles from December 18 in view of the massive air pollution in Delhi.

A 15-year-old petrol-run vehicle in India and its 10-year-old diesel counterpart are likely to have a BS-III (Bharat Stage 3) engine. The BS-IV engines were launched the next year.

Earlier, the Supreme Court, acting on a petition from the Delhi government, had ordered that no strict action would be taken against 10-year-old diesel and 15-year-old petrol vehicles. That left a grey area both for vehicle owners and the implementing agencies.

Why did the Supreme Court issue this clarification?

The court's clarification came today following a request from the Central pollution watchdog CAQM (Commission for Air Quality Management). Citing the extreme pollution blanket over Delhi-NCR, the Commission had asked that vehicles with older engines (BSIII) contribute massively to pollution and deserve no exemption.

The crackdown on older engines came after evidence mounted that vehicular pollution remained the key reason for the smog blanket over Delhi every winter.

How serious is vehicular pollution in Delhi-NCR?

The CAQM has found that around 93 per cent of the 2.88 crore vehicles on the road in Delhi-NCR are light motor vehicles, including cars and two-wheelers. Around 37 per cent run on BS III or even older engines. These emit between 2.5 and 31 times more particulate matter, 6.25 to 12 times more nitrogen oxides, and 1.28 to 5.4 times more carbon monoxide compared to newer vehicles, the CAQM said in the data submitted to the top court.

As the AQI in Delhi keeps spiralling, the Prime Minister's office has ordered strict action against polluting vehicles.

What measures are being taken to curb pollution?

On Wednesday, Delhi environment minister Manjinder Singh Sirsa announced a series of new steps to address vehicular pollution. These include not providing fuel to a vehicle without a valid PUCC certificate, an integrated traffic system that will cut down on time and pollution at traffic lights, and a cap-pooling app.