Bharat stage is very similar to that of the euro norms followed in Europe. India started making norms for emissions in 1991 and as days passes by, this norms are becoming more strict.
Transportation industry is the second most non-green industry in the world and road vehicles are one of the reasons for it. Internal combustion engines powering these vehicles produces pollutants such as carbon monoxide, hydrocarbons, NOx and particulate matter to the environment. These have caused and still causing lots of problems such as ozone layer depletion, health hazards, smog and also, they are responsible for global climate change. Therefore, government all over the world are bringing stringent norms to control this pollution by setting maximum amount of pollutants that a vehicle can release to the air (in milligrams per kilometre). Just like the euro standards followed in the Europe we have the Bharat stage. BS-1 was adopted in nationwide during the year 2000 followed by BS-2, BS-3 and now the manufacturers follow the BS-4 standards. One thing to be noted here is that even before introducing the BS norms, the government had similar norms starting from the year 1991 for gasoline engines and 1992 for diesel engines. Given below is the list of Bharat stages along with year and place of implementation.
As the table depicts, these norms were not implemented all over the nation at the same time rather it is implemented in the areas where pollution is high (Metros and major cities) at first and then to the other parts sometime later. Coming to BS-5 and BS-6, these were proposed to be implemented in the year 2022 and 2025 but the government had made a bold decision to prepone the timeline and implement BS-6 by 2020 skipping BS-5. This is because of the increased amount of pollution in places like Delhi.
Even before the vehicle manufacturers the oil refineries must be ready with the BS-6 compliant fuel well before the scheduled date. This is not an easy task. The refineries must adopt the required technology to produce the fuel which would cost several thousand crores. Lots of R and D works. This explains why the government skipped the BS-5 as this would cost more money and time to achieve and moreover, the European countries have implemented Euro-6 long ago in 2016 which would make us lag by 10 years. BS-6 compliant fuel is already available in Delhi (see table) and will be sold in the other parts of the country before 2020. This fuel has very less sulphur content (10 ppm compared to 50 ppm of BS-4 compliant fuel). The refineries must be very strict to the due as once if the manufacturers started rolling the BS-6 compliant cars out of their factories, and there is no BS-6 fuel, these cars cannot run on BS-4 fuel. Also, neither the new fuel will affect the old BS-4 compliant cars nor will produce noticeably better emissions.
The data above shows a great improvement in a span of 30 years we have reduced the amount of pollution from several grams to almost a milligram. These data are for the M and categories which includes cars and pickup trucks. ARAI also released such data for bikes, trucks, generators, etc. This can be seen in their website (click the link below to download this pdf.) Coming to the auto makers side, ARAI has issued the ceiling values of the amount of pollutants (in mg per km) which every vehicle rolling out of the production line must be compliant. BS-6 vehicles use Selective catalytic reduction technology and many other parts must be altered or changed. The main disadvantage here is, the cost of vehicle might increase and some cars like Omni are likely to be discontinued. But on the good side, lots of facelifts on the existing models can be expected, new cars may launch and cars tend to get greener and safer. All the companies are working hard for this yet there is less pressure in some companies which are already having the required technology in India as they export Euro-6 vehicles to many European countries from India. Mercedes has gone a step further and they have launched BS-6 compliant vehicle well ahead of the schedule and the interesting part is that it runs on BS-4 fuel. It uses AdBlue to achieve this and making it the first vehicle manufacturer to produce BS-6 vehicle in India.
For more information check: https://www.araiindia.com/pdf/Indian_Emission_Regulation_Booklet.pdf