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The Leap From BS-IV To BS-VI. Why Is It Such A Big Deal? Emission Norms Explained.


By Hitee Singh

A month ago the government made the decision of jumping from the current BS-IV to BS-VI auto emission norms after a meeting of the Ministries for Road Transport, Petroleum, Heavy Industries and Environment. This step is in line with the promises made by India in the climate Change Conference held in Paris.

What are BS Emission Norms?

Bharat Stage or BS are auto emission standards constituted by Indian Government to regulate the output of air pollutants from internal combustion equipment that includes motor vehicles. The standards and the timeline for implementation are set by the Central Pollution Control Board under the Ministry of Environment & Forests and climate change. The standards are based on European Emission Norms but lag behind by 5 years.

BS-IV norms are currently applicable in only in 33 Indian cities and the rest still follows the BS-III norms. Previously, BS-V norms were to be implemented from 1st April 2022 and BS-VI norms were to be implemented from 1st April 2024. But now the government wants to jump to BS-VI from 1st April 2020 by skipping BS-V norms altogether.


What are BS-IV, BS-V, and BS-VI norms?

BS-IV norms call for 2 and 3 wheeler manufacturers to fit an evaporative emission control unit, which should lower the amount of fuel that is evaporated when the motorcycle is parked.

BS-V norms require a Diesel Particulate Filter (DPF) to be mounted on the motor vehicles as it removes particulate matter or soot from diesel exhaust.

BS-VI norms require Selective Catalytic Reduction (SCR) module be mounted inside the motor vehicle.



The oil companies have a huge challenge ahead of them to upgrade fuel quality from BS-III and BS-IV standards to BS-VI which is sure to cost a lot of money. The government still hasn’t been able to produce BS-IV petrol and diesel because the refiners have been unable to do so.

It is tough for the automakers to quickly make the design changes in their vehicles as both DPF and SCR will have to be adapted to India’s conditions, where running speed of the vehicles is much lower to that in Europe or the US.

DPF needs temperatures of 600° C which are difficult in Indian conditions. Small cars would be needed to be redesigned to accommodate the DPF, making the bonnet larger, breaching the sub-4m mark and losing excise benefits.


SCR reduces oxides of nitrogen by inserting an aqueous solution (AUS 32) into the system. AUS 32 comprises of ammonia, for which a separate container needs to be put. An anti-defect mechanism is needed in case the AUS 32 is not re-filled. Infrastructure is needed for the supply of AUS 32.

Even today BS-IV isn’t applicable in all the states, leaving interstate buses and trucks to stay on with BS-III norms.

Particulate Cuts

BS Norms Diesel Cars Heavy Trucks
BS-III to BS-IV 50 % Decrease 80 % Decrease
BS-IV to BS-V 80 % Decrease No Change
BS-V to BS-VI No Change 50 % Decrease

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