Bharat Stage Emission Standards (BSES) are emission standards instituted by the Government of India to regulate the emission from the output of air pollutants from the compression ignition engines and spark ignition engines. This emission standards are for both heavy vehicles and light vehicles.
Emission standards are the standards set for the requirement of specific limits sets to the amount of air pollutants that can be released into the environment. The standards are set by the Central Pollution Control Board under the Ministry of Environment, Forest and Climate Change.
Emission standards are based on European regulations as it first introduced in 2000. All the vehicles manufactured after the implementation of norms have to be complaint with the regulations. In 2010, Bharat Stage (BS) norms have been enforced across the country.
Many emission standards focus on regulating pollutants released by an automobile, motor vehicles and other transport vehicles but they can also be regulating the emission from industries, large scale manufacturing companies, factories, small industries, power plants and small equipment’s such as diesel generators and lawn movers.
Emission standards are generally regulating the emission of NOx, particulate matter (PM) or soot, volatile hydrocarbon and carbon monoxide.
Since the year 2000, India started adapting the European emission and fuel regulations for four wheeled light duty and heavy-duty vehicles. On he year 2003, the National Auto Fuel Policy has been announced in which the phased program for Euro emission 2-4 emission and fuel regulation by the year 2010.
The table below shows implementation for the Indian Emission Standard for four-wheeler vehicles are as follows,
| Standard | Reference | Date | Region |
| India 2000 | Euro I | 2000 | Nationwide |
| 2001 | NCR-Mumbai | Kolkata | Chennai |
| Bharat Stage II | Euro II | 2003-04 | NCR (10 cities) |
| 2005-04 | Nationwide | ||
| Bharat Stage III | Euro III | 2010-14 | Nationwide |
| Bharat Stage IV | Euro IV | 2010-14 | NCR |
The 10 cities include Mumbai, Chennai, Kolkata, Bangalore, Hyderabad, Pune, Kanpur, Surat, Agra and Ahmedabad.
Since the year 2020, the Central Government of India mandated that every two-wheeler and four-wheeler manufacturers, ought to manufacture, sell and register solely BS6 (BSVI) vehicles. As compared to BS4, the BS6 standards are stricter and the manufacturers can update their vehicles with new variations and safety options.
The table below shows the permissible emission levels of BS6 vehicles as compared to BS4 vehicles as,
| Fuel Type | Pollutant Gases | BS6 (BSVI) | BS4 (BSIV) |
| Petroleum Distilled Vehicles | Nitrogen Oxide (NOx) Limit | 60 mg | 80 mg |
| Particulate Matter (PM) Limit | 4.5 mg/km | – | |
| Diesel Fuel Vehicles | Nitrogen Oxide (NOx) Limit | 80 mg | 250 mg |
| Particulate Matter (PM) Limit | 4.5 mg/km | 25 mg | |
| HC + NOx | 170 mg/km | 300 mg |
Moving to BS6 will require technological upgrades and safety upgrades in two wheelers and four vehicles.
