Vehicle emissions and Bharat Stage norms
Vehicles emit carbon monoxide (CO), hydrocarbons (HC), oxides of nitrogen (NOₓ) and particulate matter (PM), especially from diesel engines. India controls these through Bharat Stage (BS) emission standards, based on European (Euro) norms. Each new stage sets tighter limits and needs cleaner fuel.
- BS-I came in around 2000; BS-IV became nationwide in April 2017.
- India skipped BS-V and moved directly to BS-VI from 1 April 2020 across the country.
- BS-VI fuel contains at most 10 ppm sulphur, far less than BS-IV fuel (50 ppm).
A catalytic converter, fitted in the exhaust, uses metals such as platinum, palladium and rhodium to convert CO → CO₂, unburnt HC → CO₂ + H₂O, and NOₓ → N₂. It needs unleaded petrol, because lead “poisons” the catalyst. India phased out leaded petrol by 2000.
The CNG programme in Delhi
In the 1990s Delhi’s air was among the most polluted in the world. In the M. C. Mehta v. Union of India case, the Supreme Court in 1998 ordered Delhi’s buses, autorickshaws and taxis to switch to compressed natural gas (CNG). The changeover was largely completed by about 2002–03. CNG burns more cleanly, giving far less PM and SO₂. Other measures included phasing out old vehicles, metro rail and stricter fuel norms.
Industrial emissions
Thermal power stations, cement, steel and brick kilns emit dust, SO₂ and NOₓ. Control devices:
- Electrostatic precipitator (ESP): charges particles and collects them on plates; can remove over 99% of particulates from chimney gases.
- Scrubbers: spray water or lime slurry to remove gases like SO₂ (flue gas desulphurisation).
- Cyclone separators and bag (fabric) filters for dust.
- Tall stacks only spread pollution over a wider area; they do not remove it.
Key points
- BS-VI nationwide from 1 April 2020; BS-V skipped.
- BS-VI fuel: ≤ 10 ppm sulphur.
- Catalytic converter needs unleaded petrol.
- Delhi CNG: Supreme Court order, 1998.
- ESP → particulates; scrubber → gases such as SO₂.
Exam tips
Match devices to pollutants: ESP for particles, scrubber for SO₂, catalytic converter for vehicle CO, HC and NOₓ. Know the BS-VI date and that BS-V was skipped.
Common mistakes
- Thinking India adopted BS-V before BS-VI.
- Saying an ESP removes SO₂; it removes particles.
- Thinking a catalytic converter removes CO₂; it produces CO₂ from CO.