Bharat Stage (BS) Emission Norms

Bharat Stage (BS) norms are the rules that fix how much pollution a new vehicle is allowed to release from its exhaust pipe in India. The government sets the maximum amount of harmful gases and tiny particles a car, bike, bus or truck may emit for every kilometre it runs. A vehicle must pass these limits before it can be sold. Each new "stage" (BS-I, BS-II and so on) is stricter than the one before, so newer vehicles pollute less.

Why do we need emission norms?

Petrol and diesel engines burn fuel to create power. This burning also produces harmful gases like carbon monoxide and nitrogen oxides, and tiny soot particles. In crowded Indian cities, millions of vehicles release these gases at the level where people breathe. Without fixed limits, companies would have little reason to spend money on cleaner engines, and city air would keep getting worse. Emission norms force every manufacturer to meet the same clean-air standard.

Where did they come from?

• India's first vehicle emission rules came in the early 1990s. The first proper national norm, called "India 2000" (later known as BS-I), came in 2000. It was modelled on Europe's Euro I standard.
• A committee led by scientist R.A. Mashelkar gave a roadmap in 2002. The National Auto Fuel Policy, 2003 accepted it and set dates for BS-II, BS-III and BS-IV.
• BS-II applied across the country from 1 April 2005, when 13 big cities moved to BS-III.
• BS-III became nationwide in 2010, and BS-IV started in 13 big cities in April 2010.
• BS-IV became nationwide from 1 April 2017.
• In 2016, the government decided to skip BS-V and jump straight to BS-VI, which came into force nationwide on 1 April 2020. BS-VI fuel reached Delhi early, from 1 April 2018.
• On 24 October 2018, in M.C. Mehta v. Union of India, the Supreme Court ordered that no BS-IV vehicle could be sold or registered anywhere in India from 1 April 2020. It relied on the right to health and a clean environment under Article 21.

Who makes the rules?

Two ministries share the work, because a clean engine needs clean fuel too.

• Vehicle norms: MoRTH notifies them under the Central Motor Vehicles Rules, 1989 (mainly Rule 115). These rules are made under the Motor Vehicles Act, 1988.
• Fuel quality: The Ministry of Petroleum and Natural Gas makes sure oil companies sell matching fuel (for example, low-sulphur BS-VI petrol and diesel).
• Testing: Government-approved agencies like the Automotive Research Association of India (ARAI), Pune, and the International Centre for Automotive Technology (ICAT), Manesar, test new models before approval. This approval is called type approval.

How does a vehicle get tested?

A new model is run on a machine called a chassis dynamometer. You can think of it as a treadmill for cars. The car "drives" a fixed pattern of speeding up, slowing down and stopping, called a driving cycle, while machines collect and measure the exhaust. If the amounts are below the limits for each pollutant, the model passes. The problem is that a laboratory is not a real road. A car may pass in the lab but pollute much more in real traffic.

What did BS-VI change?

BS-VI was a very big jump over BS-IV, especially for diesel vehicles.

• Sulphur in fuel fell from 50 ppm (parts per million) to 10 ppm. Less sulphur means less soot and allows modern pollution-control devices to work.
• For diesel cars, the NOx limit fell from 250 mg/km to 80 mg/km, and the particulate matter limit fell from 25 mg/km to 4.5 mg/km.
• For petrol cars, the NOx limit fell from 80 mg/km to 60 mg/km. The carbon monoxide limit stayed at 1,000 mg/km.
• A limit on particle number (PN, the count of particles, not just their weight) was added.
• BS-VI Phase 2 (from 1 April 2023) added Real Driving Emissions (RDE) checks and stricter On-Board Diagnostics (OBD-II).

How is BS-VII different?

The proposed BS-VII norms keep similar exhaust numbers for petrol and diesel cars as BS-VI. For example, the draft sets CO at 1,000 mg/km for petrol and 500 mg/km for diesel, and NOx at 60 mg/km and 80 mg/km. The big change is in what is measured and for how long:

• Real-world testing: On-road tests with portable machines become part of type approval from April 2030, with a conformity factor of 1.0 for NOx and particle number. This means the car must meet the same limit on the road as in the lab, with no extra margin.
• Longer durability: Cars must stay within limits for 1,60,000 km or 8 years, with a further lifetime period up to 2,00,000 km or 10 years.
• On-board monitoring: The car itself must watch its emissions and fuel or electricity use, and report problems.
• Non-exhaust pollution: Limits on brake dust and tyre wear are added for the first time (see the next bridge).
• Fuel-neutral and EV-inclusive: The same limits apply to petrol (including E20), diesel, CNG, LPG, hydrogen, methanol, flex-fuel and hybrids. EVs face battery-durability and brake-dust rules. This approach is close to the European Union's Euro 7 regulation (Regulation (EU) 2024/1257), adopted in 2024, which also added brake-dust and battery rules.

India's position and examples

• India's BS stages follow the Euro series. BS-VI is broadly equal to Euro 6.
• Skipping BS-V meant Indian carmakers and oil refiners had to upgrade in about four years instead of eight. Oil companies spent heavily on refinery upgrades to produce 10 ppm fuel.
• Vehicles are a major source of city air pollution, especially in Delhi and other northern cities, so BS norms are a key part of India's clean-air plans, along with the National Clean Air Programme (NCAP).

Commonly confused concepts

• BS norms vs CAFE norms: BS norms limit harmful pollutants (CO, NOx, PM) from each vehicle model. CAFE (Corporate Average Fuel Efficiency) norms limit the average fuel use or CO₂ of all cars a company sells in a year. CAFE is run by the Bureau of Energy Efficiency (BEE) under the Ministry of Power. A draft CAFE-III was released in July 2026 for 2027-28 to 2031-32.
• BS-VI vs Euro 6: They are broadly similar, but the Indian version uses its own driving cycle (the Modified Indian Driving Cycle, MIDC) that suits Indian road conditions.
• Emission norms vs fuel standards: Emission norms apply to vehicles; fuel standards (like 10 ppm sulphur) apply to petrol and diesel. Both have to move together.
• Exhaust vs non-exhaust emissions: Exhaust comes out of the tailpipe. Non-exhaust comes from brakes, tyres and road dust, and even EVs produce it.

Issues, criticism and the way forward

• Lab vs road gap: Studies around the world have shown that real-road emissions can be far higher than lab results. RDE tests and on-board monitoring try to close this gap.
• Cost for buyers and makers: Cleaner technology makes vehicles costlier, especially small diesel cars. Some makers stopped selling small diesel cars after BS-VI.
• Old vehicles: Norms apply only to new vehicles. Old, poorly maintained vehicles on the road keep polluting. Vehicle scrapping policy and pollution-under-control (PUC) checks are the tools for this.
• Enforcement: In-service checks on vehicles already on the road have been weak. BS-VII's in-service conformity and durability rules aim to fix this.
• Way forward: Experts suggest strict testing by independent agencies, better PUC systems, faster EV adoption and rules for non-exhaust pollution, which BS-VII starts to address.

Concepts to Know

• Carbon monoxide (CO): A poisonous gas with no colour or smell. It forms when fuel does not burn fully. It reduces the blood's ability to carry oxygen.
• Nitrogen oxides (NOx): Gases formed when air is heated to very high temperatures inside an engine. They harm the lungs and help form smog and ground-level ozone. Diesel engines produce more NOx.
• ppm (parts per million): A way to measure very small amounts. 10 ppm sulphur means 10 grams of sulphur in every 10,00,000 grams (one tonne) of fuel.
• mg/km: Milligrams of a pollutant released for every kilometre a vehicle runs. A smaller number means a cleaner vehicle.
• Type approval: The official certificate that a new vehicle model meets all safety and emission rules before it can be sold.
• Real Driving Emissions (RDE): A test where the car is driven on real roads with a Portable Emission Measurement System (PEMS) fitted to it, instead of only in a lab.
• On-Board Diagnostics (OBD): A computer system inside the vehicle that checks if the pollution-control parts are working and warns the driver with a light if something fails.
• Category M1: Vehicles for carrying passengers with not more than eight seats in addition to the driver's seat, basically cars and SUVs.
• E20: Petrol mixed with 20% ethanol, a fuel made mostly from sugarcane and grains.