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About BSES

The Bharat Stage Emission Standards (BSES) are government-set regulations imposed on vehicular emissions of all types in India. The first emission norms were enforced in the year 2000, known as ‘India 2000’. Following this, BS2 and BS3 were introduced in the years 2005 and 2010, respectively.

What is BS4 (BS-IV)?

Bharat Stage 4 (BS4 or BS-IV) came into effect in 2017 and primarily focused on making emission standards more stringent. Some of the emission-related changes in BS4 involve tailpipe emission, Electronic Control Unit (ECU), ignition control, and so on.

What is BS6 (BS-VI)?

The standards to maintain vehicle emissions’ output are set by the Central Pollution Control Board, which is further governed by the Ministry of Environment, Forest, and Climate Change.

The BS6 emission norms push to reduce pollution even further compared to the BS4 standards.

Difference Between BS4 and BS6 Engines

Here are a few key differences between BS4 and BS6 emission norms:

  1. With the implementation of BS6 standards, Diesel Particulate Filter (DPF) and Selective Catalytic Reduction (SCR) have been established as well. This was not present in the previous BS norms.

  2. Along with the implementation of BS6 emission norms, India is all set to introduce the Real Driving Emission (RDE). It is said to measure the real-time emission from vehicles against the laboratory conditions. The same was not a part of BS4 emission norms.

  3. Onboard Diagnostics (OD) is now mandatory for all vehicles under the BS6 emission norms.

  4. As the BS6 emission norms come into play from April 1, 2020, there is also a change in the fuel used in vehicles. Thus, the vehicles that are BS6-compliant will require BS6 fuel. If the vehicles happen to use BS4-grade fuel, it will not adhere to the BS6 emission norms. Likewise, if BS4-compliant vehicles use the BS6 fuel, its engine will be affected and emission will increase.

  5. Another crucial difference between the two is in terms of sulphur and nitrogen oxide emissions. The trace of sulphur in BS6 fuel is five times less than in BS4 fuel. Moreover, nitrogen oxide levels of BS6 diesel and petrol engines are said to be brought down by 70 percent and 25 percent, respectively.

To understand the difference between the permissible emission norms of BS4 vehicles and BS6 vehicles, consider the following table:

Fuel Type




Petrol-Based Vehicles

Nitrogen Oxide (NOx)

80 mg

60 mg

Particulate Matter (PM)


4.5 mg/km

Diesel-Based Vehicles

Nitrogen Oxide (NOx)

250 mg

80 mg

Particulate Matter (PM)

25 mg

4.5 mg/km

HC + NOx

300 mg/km

170 mg/km

BS-I, BS-II, BS-III, BS-IV, and BS-VI Emission Norms

The emissions standards are denoted by the abbreviation ‘BS’, i.e. Bharat Stage, followed by its respective iteration. Emission levels in India are based on the European norms, also known as EURO 1, EURO 2, and so on. Each iteration imposes more stringent permissible emission standards compared to the previous one.

As mentioned earlier, BS3 standards were introduced in the year 2010, whereas BS4 was introduced in the year 2017. Since there was a significant delay between the implementation of BS3 and BS4 standards, BS6’s introduction was fast-tracked, replacing BS5 altogether.

To get an overview of the emission standards implemented along with their timelines, consider the following table:

Emission Standard

European Norm Reference

Implementation Year

India 2000



Bharat Stage II (BS2)



Bharat Stage III (BS3)



Bharat Stage IV (BS4)



Bharat Stage V (BS5)



Bharat Stage VI (BS6)



What are the Benefits of a BS6 Engine?

The advantages of moving from BS4 to BS6-compliant vehicles are as follows:

  • The BS6 emission norms are said to reduce nitrogen oxide emissions by 25 percent in petrol cars.

  • Due to the upgrade in the engine control software, there is more precise fuel injection control for cleaner emission control.

How Does the BS6 Diesel Engine Work?

In technical terms, the Selective Catalytic Reduction (SCR) unit converts nitrogen oxide (NOx) to diatomic nitrogen and water (harmless entities). The SCR unit uses AdBlue or diesel exhaust fluid to reduce NOx emission. This fluid is made up of urea and deionised water. So, when the exhaust gases get mixed with this fluid, urea is converted into ammonia and CO2. Further, ammonia converts NOx into nitrogen and water vapour. Overall, this process helps reduce the content of pollutants from vehicular emissions.

Health and Environmental Consequences of Vehicle-Generated Air Pollution in India

Air pollution caused due to vehicle-generated emission can have immediate and long-term effects on the environment, including us. As stated earlier, motor vehicles emit several harmful gases and particulate matter, which leads to air pollution.

Following are the consequences of vehicle-generated air pollution:

  • Global Warming

One of the major consequences of air pollution due to vehicle emissions is global warming. Motor vehicles emit carbon dioxide and other harmful gases that contribute to the pollution levels. Since these harmful gases stay trapped in our environment, it leads to a rise in overall temperatures across the world, i.e. global warming. Furthermore, this increase in temperature can have adverse effects on farming, wildlife, sea levels, and landscapes.

  • Impact on Air, Soil, and Water

Vehicle-generated air pollution can affect the quality of air, soil, and water in our environment. One of the harmful gases emitted by motor vehicles is nitrogen oxide, which leads to the depletion of the ozone layer. The ozone layer protects our Earth and its environment from the harmful UV rays of the sun. On the other hand, sulphur dioxide and nitrogen dioxide mix with rainwater to produce acid rain, which further affects farming, forests, and our infrastructure. Oil and fuel spills from motor vehicles can seep into the earth, affecting cultivation. Further, when the same is discarded in the water, it can contaminate water bodies and disrupt marine life.

  • Impact on Human Health

Much like the environment, humans are vulnerable to these harmful pollutants as well. People across India suffer from several health issues caused due to breathing unhealthy air. As such, there has been a significant rise in skin infections, allergies, and respiratory issues over the last few years. Moreover, the harmful emissions from motor vehicles can even lead to heart diseases in senior citizens and infants.

Over to You

We hope this article helps you understand the difference between BS4 and BS6 engines. So, if you are planning to buy a new vehicle this year, you’ll be well-informed to make the right decision.

Just like choosing between BS4 and BS6 engines is imperative to stay compliant with the emission norms, so it is essential to choose an ideal vehicle insurance plan. Selecting the right car insurance plan will allow you to financially safeguard your vehicle in case of an accident. In fact, you can compare different vehicle insurance plans online and choose one that fulfils all your requirements.

Download the Finserv MARKETS’ Car Insurance App to choose an insurance plan that best suits your needs. You can also check the premiums on car insurance plans available on Finserv MARKETS by using our car insurance calculator. The tool not only provides premium quotes, but also allows you to compare quotes from different insurers. Based on the results, you can then choose a car insurance plan that is affordable and meets your requirements.

Check Out Car Insurance Plans Available at Finserv MARKETS


  • ✔️What if BS4-compliant cars are filled with BS6 fuel?

     If BS4-compliant vehicles are filled with BS6 fuel, it may affect the engine and increase the emission.

  • ✔️Can BS6-compliant cars run on BS4-grade fuel?

     While BS6-compliant vehicles can run on BS4 fuel, it will not comply with the BS6 emission norms.

  • ✔️Between BS6 fuel and BS4 fuel, which is cheaper?

    The prices of BS6 and BS4 fuels are not significantly different. However, after BS6 is implemented across the nation, the prices may fluctuate. This is due to input costs incurred by the Oil Marketing Companies (OMCs) when updating facilities on their side.

  • ✔️Is it possible to convert my old car to fit the BS6 emission norms on my own?

     No, it is illegal to convert your old car to fit the BS6 emission norms.

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