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Vehicular pollution: What is BS and why should you care?

New emissions for vehicles in India which come into effect on April 1, will mean costlier cars and fuel, but will eventually cut cost of health care because of pollution induced health problems will fall.

india Updated: May 11, 2017 17:11 IST

India will switch to BS IV emission norms for vehicles from April 1. The switch is expected to significantly bring down vehicular pollution in the country.(HT Photo)

The Supreme Court on Wednesday said the health of citizens was more important than commercial interests of auto makers as it banned the sale and registration of Bharat Stage (BS)-III emission norm-compliant vehicles from April 1.

Here is a low-down on vehicular emissions.

What are emission norms?

Bharat Stage or BS norms are standards for vehicular emissions. They lay down the permissible levels of pollutants that come out of the exhaust pipes of motor vehicles. The aim is to check air pollution and emissions that lead to global warming.

Why are we talking about it right now?

India is set to enforce a new generation of vehicular pollution norms on April 1 called BS IV. The norms are already in place in some cities but starting April only BS IV compliant vehicles can be manufactured, sold and registered, across the country.

What is the possible impact on air pollution?

Delhi-based policy think-tank, Centre for Science and Environment, estimates that the transition will lead to a significant decrease in PM emissions. Emissions can fall by as much as 80% from new trucks and by 50% from cars.

Reductions in Hydrocarbon and NOx emissions from may come down by 41-80 % depending on the engine size.

What is BS-IV? What is the difference between various emission norms?

The difference between BS III and BS IV is that the latter are stricter and permit lower quantities of pollutants to be emitted by vehicles.

For passenger vehicles this is how much the permissible levels for different pollutants have changed since emission norms were adopted in the country:

NormsCO (g/km) Carbon MonoxideHC (Hydro carbons)+ NOx Nitrogen Oxides (g/km)RSPM (Respirable Suspended Particulate Matter)Sulphur Content in Diesel
  BS I2.720.970.14NA
  BS II2.20.50.08500 PPM
  BS III2.30.35 (Combined)0.050100 PPM
  BS IV1.00.18 (Combined)0.02550 PPM

Why is the Supreme Court verdict important?

There has been a recent controversy surrounding the transition from BS III to BS IV because automakers want to be able to sell vehicles after the April 1 deadline. They argued that the transition meant a ban on only the production of BS III vehicles.

SIAM, an industry group representing 48 major automakers, estimated that a stock of about 8 lakh BS III vehicles worth almost Rs 12000 crore might remain unsold because of the transition.

What does it mean in terms of implementation?

BS IV vehicles are less polluting than BS III vehicles, but better technology means that the vehicles cost more than BS III vehicles.

The implementation happened in a staggered manner, with stricter norms being implemented in major cities before becoming nationwide. For 4-wheeler passenger cars stricter norms have been in place in 13 major cities like Delhi NCR since 2010.

Nationwide norms will help check air pollution because automakers and users will not be able to take advantage of lax norms in other parts of the country. For example, some owners purchase and register cheaper BS III vehicles outside Delhi NCR, but they ply on Delhi roads, contributing to air pollution in the capital.

What about the fuel?

To meet BS IV norms not only do the vehicles have to be better at utilising the fuel, the fuel itself has to be of better quality. The ministry of petroleum and natural gas has taken the responsibility of ensuring that all the fuel supplied across the country is BS IV compliant.

BS IV fuel being cleaner will run the BS III engines too. However, the other way round will damage the engine.

What can automakers do with their BS III inventory?

They’ll have to rework only the engines and the exhaust systems in some vehicles. In stocks as old as 3 years or more with no scope of correction or alteration, scrapping would be the last resort.

How many vehicles in India?

Domestic Motor Vehicle Sales

•Passenger Vehicles: 2.79 million units

•Commercial Vehicles: 0.69 m

•Two-wheelers: 16.50 m

•Three-wheelers: 0.54 m

•Total: 20.47 million units

(Apr 2015 - Mar 2016)

Production of vehicles grew from around 5 million in 2000-01 to 14 million in 2009-10, and to 23.96 million in the fiscal 2015-16 (Source: SIAM/ ACMA data).

How deadly is vehicular pollution?

Data is not available for the whole country, but a 2015 IIT Kanpur study looking at air pollution in Delhi found:

Contribution of vehicles to PM 10 load: 9 %

Contribution of vehicles to PM 2.5 load: 20 %

Environmentalists argue that this is a conservative estimate. Though estimates vary, vehicles are recognised as a major source of air pollution.

If you took a look at the quantity of different kinds of pollutants found in the air that came from vehicles it would look something like this:

PollutantPollution load (in ton/day)
  Carbon Monoxide217.7
  Nitrogen oxides84.1
  Particulate Matter9.7
  Sulphur Dioxide0.72

Why should you care?

Particulate Matter has been linked with rising incidence of cancer, especially lung cancer. Sustained exposure to high concentrations of small particulates can lead to premature deaths. More than 1 lakh premature deaths in India in 2015 can be attributed to PM 2.5 pollution, according to The State of Global Air report 2017.

The reaction of NOx gases in the atmosphere leads to smog and acid rain. They also contribute to Particulate Matter and surface-level ozone formation. India had the highest number of ozone-pollution related deaths.

Sulphur dioxide can combine with water and cause acid rain. Acid rain damages trees and can contaminate water bodies apart from degrading infrastructure. Even monuments like Taj Mahal are not immune to the effects of acid rain.

Nitrogen Oxides: Nitrogen dioxide and nitric oxide are referred to together as oxides of nitrogen (NOx). When nitrogen is released during fuel combustion it combines with oxygen atoms to create nitric oxide (NO). Nitric oxide is not considered to be hazardous to health.

But it can become harmful when it combines with oxygen to create nitrogen dioxide (NO2). Nitrogen dioxide causes irritation in the respiratory tracts and exposure to high concentrations of it can cause inflammation of the air passage.

Reaction of NOx gases leads to smog and acid rain. They are also key to the formation of Particulate Matter and surface-level ozone.

Surface level Ozone has been known to cause adverse health effects. The State of Global Air report 2017, released this February, reported that India had the highest number of ozone-pollution related deaths and the numbers have increased from 43,480 in 1990 to 107,770 in 2015.


Sulphur dioxide can affect the respiratory system and the functions of the lungs and causes irritation of the eyes. It can combine with water and cause acid rain. Acid rain damages trees and can contaminate water bodies apart from degrading infrastructure. Even monuments like Taj Mahal are not immune to the effects of acid rain.

What would this cost you?

The average price hike of vehicles is expected to be around 10%. It will vary from company to company and model to model in different segments. Some models may be launched with revised engines to suit the norms and some automakers are also revealing BS IV specific models.

It will also nudge up the price of fuel marginally.

In the long run, healthcare costs associated with air pollution-related health will fall.

What next?

The government in January 2016 announced that India will be skipping BS V norms and enforcing BS VI norms starting 2020.