Emission Norms – Fuss or Desideratum?

Emission Norms – Fuss or Desideratum?

With the recently imposed ban on BS-III (Bharat Stage 3) vehicles; the manufacturers had to sell out huge chunks of their vehicles in highly discounted prices, as Supreme Court of India upheld their decision to ban the sales of BS-III compliant vehicles from 1st April, 2017. Though the very first introduction of BS-IV norms came into picture in 2010, it took 7 years to make it a nationwide compulsion. Initially it was introduced in NCR and 13 other cities only. Now with rising pollution and stricter norms, Government of India is planning to straightaway shoot up to BS-VI norms in April 2020 by skipping the transition to BS-V norms; thus making it the fastest migration to BS-VI.

Standard Reference
Bharat Stage II Euro 2
Bharat Stage III Euro 3
Bharat Stage IV Euro 4
Bharat Stage V Euro 5
Bharat Stage VI Euro 6


As the Global Pollution levels rise rapidly, a time will come when the world will switch to Electric Vehicles, Hybrid Electric Vehicles or Vehicles running on Alternate Fuels. But with the development cost and still a very nascent market, the transition span would be high. Meanwhile, let us grasp how vehicles pollute the environment and how  we can manually know or control our vehicle’s emission health.

There are three major sources from which atmospheric pollution is caused by an automobile; Fuel Tank, Crankcase and Exhaust pipe. If the engine is carburetted then the Carburetor is also a source of pollution. A carburetor and/or fuel tank emit fuel vapour, crankcase emits blow-by gases and the exhaust pipe emits exhaust gases. All of them include pollutants, Hydrocarbons (HC), Carbon Monoxide (CO) and Nitrogen Oxides (NOx). As these pollutants are very inimical to health, emission norms had to be levied. Out of the total Automotive Air Pollution, 20% HC are emitted from fuel tank and/or carburetor, 20% HC from crankcase and 60% HC, CO and NOx from exhaust pipe.

With stricter emission norms and growing technology, three major systems have been put in place for Automotive Emission Controls :

Positive Crankcase Ventilation : This system delivers fresh air to sweep out blow-by and vapour gases, and along with them entering the engine to give the pollutants another chance to burn.


Evaporative Emission Control : This system seizes any fuel vapour coming from fuel tank and float bowl (carburetted engines) and prevents them from escaping into the atmosphere.

Exhaust Emission Control : This is an amalgamation of various systems, mechanisms and methods who work together to reduce the emissions from exhaust pipe.

There are various other mechanisms which help in keeping the pollutants in control, such as :

Crankcase Ventilation : Engines have some blow-by gases which are majorly unburnt fuel and some residues of combustion. These blow-by gases slip past the piston rings and into the crankcase. This system prevents pressure buildup, oil leaks and also removes blow-by gases to prevent formation of corrosive acids and sludge. You must have noticed corrosion at the ends of your exhaust pipes, nuts, bolts and sometimes even the header pipes. This corrosion happens due to these corrosive acids which are the result of combustion.

Use of Charcoal/Carbon Canisters : The canisters “adsorbs” the fuel vapour. “Adsorbs” means that the vapour is not absorbed but trapped onto the outer layer. Later, when the engine is run, fresh air flows through the canister and picks up the fuel vapour.


Cleaning of Exhaust gases : The combustion in engines is never complete and some unburnt fuel (HC) and CO (partly burned fuel) always remain in the exhaust gas. More HC would burn with higher combustion temperature but higher combustion temperature would lead to more NOx gases. There are two simple ways to go around this issue :

  • Controlling the fuel quality (by checking the octane rating of fuel which you fill up)
  • Controlling the air-fuel mixture (by having your system deliver a leaner air-fuel mixture)

Exhaust Gas Recirculation : Excessive NO2 gases are formed when peak combustion temperature exceeds 1927 oC, and to lower this temperature many engines use EGR system. It is used to recirculate 6% to 13% of inert exhaust gases back into the intake manifold. EGR system is also equipped with back-pressure sensor and is controlled by ECM.

Catalytic Converter : The catalytic converter converts pollutants into harmless gases by causing  a chemical reaction, without being the part of it. It converts HC and CO into H2O and CO2 by using platinum and palladium as oxidizing agents. While it splits NOx and makes it into harmless nitrogen and oxygen, by using rhodium as the reducer. There are also Dual-Bed and Three-Way Catalytic Converters.


There are still various systems and checks the manufacturers need to go through before releasing them into the market, just to meet the emission norms. But to save our own environment these steps are unquestionably necessary. These are the systems which are in the control of the buyers, so we highly recommend you all to keep a check on these systems, service them regularly and always periodically get your PUC certificate.


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