
The evolution of vehicular emission standards is akin to upgrading the filters in our homes to keep the air we breathe purer and healthier. Just as these filters trap more dust and impurities over time, India's Bharat Stage (BS) emissions standards have been designed to steadily reduce the harmful pollutants emitted by vehicles. Implemented in April 2020, the BS6 emission norms marked one of the most significant transitions in India’s vehicular regulation history, with Phase 2 now in effect since April 2023. These norms not only align India with the world’s best standards but also underline the country’s commitment to cleaner air, safer roads, and a greener future. So, what sets BS6 apart from its predecessors, and how has it already begun reshaping the Indian automotive landscape?
A Leap from BS4 to BS6: What Changed?
BS6 is India’s sixth stage of emission norms for vehicles, replacing the BS4 norms that were enforced until March 2020. The primary goal of BS6 is to bring down the levels of harmful gases like nitrogen oxides (NOx), carbon monoxide (CO), particulate matter (PM), and hydrocarbons (HC), which contribute heavily to air pollution.
A few critical changes stand out when comparing BS6 with BS4:
Drastic Reduction in Pollutants: BS6 fuel contains only 10 ppm (parts per million) of sulphur, five times lower than BS4’s 50 ppm. This reduction has a direct impact on emissions, particularly in the volume of particulate matter (PM 2.5) emitted, making BS6 fuel much cleaner.
Nitrogen Oxides (NOx) Reduction: Diesel vehicles now emit 70% less NOx, and even petrol engines have achieved a 25% reduction in NOx emissions under BS6 norms.
Introduction of Diesel Particulate Filters (DPF): Diesel vehicles under BS6 now feature DPF, which captures and stores exhaust soot, reducing PM emissions.
Selective Catalytic Reduction (SCR): SCR technology in diesel engines further reduces NOx emissions by injecting a urea-based liquid, known as AdBlue, into the exhaust stream.

Phase 2 and Real Driving Emission (RDE) Testing: A New Benchmark
One of the most remarkable advancements under BS6 Phase 2 is the introduction of Real Driving Emission (RDE) testing, a first for India. Traditional emission testing was carried out under controlled laboratory conditions, which often failed to capture real-world emission scenarios. RDE testing measures a vehicle’s emissions in actual road conditions, providing a much clearer picture of how a car performs in everyday driving.
This shift compels automakers to comply with emissions standards in real-world situations, where variables like traffic, road gradients, and varying speeds come into play. Vehicles are now equipped with Portable Emission Measurement Systems (PEMS) to assess emissions on the go, ensuring that regulatory compliance is not just on paper but reflected in reality.
The Environmental Payoff
Cities like Delhi, Mumbai, and Bengaluru, which have been grappling with hazardous air quality levels, stand to benefit enormously. With the reduction in PM, NOx, and sulphur emissions, the air in Indian metros is expected to gradually improve, reducing respiratory issues and other health hazards associated with pollution. By curbing vehicle emissions, BS6 norms also contribute to the broader fight against climate change. The reduced release of harmful pollutants into the atmosphere slows down the pace of global warming and its associated consequences.BS6-compliant fuels lower emissions and also enhance engine health by reducing wear and tear, the lower sulphur content leads to less corrosion inside the engine.

The Impact on Automakers and Consumers
Complying with BS6 norms requires significant investments from automakers. New technologies such as Diesel Particulate Filters (DPF), Selective Catalytic Reduction (SCR), and Lean NOx Traps (LNT) must be integrated into vehicle designs, which has increased the cost of production. Consequently, buyers have seen a rise in the price of both petrol and diesel vehicles. BS6 fuel is not recommended for older BS4 vehicles, particularly diesel variants, as it could lead to engine problems over time. Components like fuel injectors and oil seals may suffer damage, resulting in increased wear and tear. The Indian government has yet to announce a comprehensive scrappage policy for older vehicles, meaning that a significant number of pre-BS6 vehicles are still on the roads, somewhat diluting the impact of the newer norms.
A Necessary Shift for a Sustainable Future
While the transition to BS6 and its subsequent Phase 2 regulations has been challenging, the long-term environmental and health benefits far outweigh the costs. Automakers are rising to the occasion, and consumers are gradually embracing the shift towards cleaner vehicles. The road to reducing air pollution and ensuring a more sustainable future is paved with these stringent norms that push for innovation and responsibility.
As India moves ahead with its ambitious goals to combat climate change and improve public health, the BS6 regulations serve as a critical milestone in the country’s ongoing journey toward cleaner and greener transportation. And as we breathe in cleaner air, the price paid today will undoubtedly prove to be a worthy investment in our collective tomorrow.