Environment › Pollution
Air pollution
Air pollution and its control: the national programme and standards, how air quality is measured and ranked, and its sources, from vehicles and power plants to crop burning, dust and indoor fuel. Prelims has asked which gases are used to calculate the Air Quality Index and about the World Health Organization (WHO) air quality guidelines.
UPSC has asked
- Prelims 2022: the WHO Air Quality Guidelines
All 5 subjects shown; the 2 that changed from 1 to 15 September 2026 are marked.Show only these
National Clean Air Programme
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The National Clean Air Programme set 130 cities a target for one pollutant and paid them to meet it. Seven years on, most of those cities have cleaner air than they started with and very few of them have clean air.
- The National Clean Air Programme (NCAP) was launched in 2019 and covers 130 cities, most of them non-attainment cities.
- It aims to cut PM10 by up to 40 per cent by 2025–26, measured against 2017–18.
- Cities are paid through performance linked grants, tracked on the Portal for Regulation of Air Pollution in Non-Attainment cities (PRANA).
- Against 2017–18, 108 of the 130 cities had lower annual PM10, 26 cut it by more than 40 per cent, and 14 met the standards.
- Of ₹16,423.55 crore in grants since 2019–20, 70.5 per cent has been used.
- The results were released on Swachh Vayu Diwas, the International Day of Clean Air for Blue Skies.
What changed
7 Sep 2026
7 Sep 2026
- Swachh Vayu Survekshan, begun in 2022–23, ranks NCAP cities in three population groups on what they do about dust, waste burning, vehicles and industry.
- It rewards effort over results: measured PM10 improvement carries only 2.5 per cent of the weightage.
- In the 2026 rankings Lucknow topped the largest cities although its PM10 is more than twice the national standard.
23 Jul 2026Update
- On the finer fraction, 65 of the 130 programme cities met the PM2.5 standard of 40 µg/m³ in 2025 to 26. Among large cities Surat, Mumbai and Hyderabad were within it, while Delhi stood at 102 µg/m³.
National Ambient Air Quality Standards
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The standards name the pollutants that must be measured in ambient air and the level each of them may reach. The Air Quality Index reduces that day's readings to a single number, and the National Green Tribunal has now asked for three more pollutants to be brought into the measuring.
- The National Ambient Air Quality Standards cover twelve pollutants, and the Air Quality Index combines eight of them, particulate matter (PM10 and PM2.5), NO₂, SO₂, CO, O₃, NH₃ and lead, taking whichever is worst.
- Carbon dioxide and methane are not among them, so the index says nothing about the greenhouse gases.
- It runs in six bands, from Good, 0 to 50, to Severe, 401 to 500.
- Ambient air is sampled manually over 24 hours and read continuously at Continuous Ambient Air Quality Monitoring Stations (CAAQMS).
- The annual PM10 standard is 60 micrograms per cubic metre, four times the World Health Organization (WHO) guideline of 15.
- The Central Pollution Control Board (CPCB) is statutory under the Water Act, 1974, and the Commission for Air Quality Management (CAQM) under its own Act of 2021.
- The National Green Tribunal gave the CPCB ten weeks to standardise testing for three further ambient air pollutants, aluminium, iron and silica.
What changed
25 Aug 2026
The Hindu, 25 Aug 2026
UPSC has asked
- Prelims 2016: the gases used to calculate the Air Quality Index
Stubble burning
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Stubble burning is a modest share of the season's particulate pollution and a large share of it on the worst days, so how the fires are counted decides how the argument runs. The satellites that count them are now missing them, because the burning has moved into the evening.
- Farm fires add no more than 15 per cent of winter particulate pollution, but more than a third on some October and November days.
- CAQM opened talks with Punjab and the Indian Space Research Organisation (ISRO) on how stubble burning is counted, doubting that fire counts capture it.
- Peak burning moved from about 1.30 pm in 2020 to about 5 pm in 2024, after the satellites have passed.
- Fire counts in Punjab and Haryana fell 93 and 91 per cent from 2021 to 2025, but burnt area fell far more slowly.
- The burnt area protocol is being re-tested as satellite and ground data diverge.
Fire counts
- Active fires seen during daytime satellite passes
- Miss fires lit after the satellites have gone
Burnt area
- Scorched fields mapped from Sentinel-2 images
- Says nothing about how much smoke a fire released
What changed
Background reading: The Indian Express, 7 Sep 2026: Air quality management body to re-test burnt area protocol as satellite, ground data diverge (opens in a new tab)
Flue gas desulphurisation norms
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Flue gas desulphurisation removes sulphur dioxide from a coal plant's exhaust, usually with a limestone slurry. It was made mandatory in 2015. A 2021 notification split plants into three categories by location, and Category C, close to four fifths of the fleet, has since been exempted. Sulphur dioxide turns into sulphate particles in the air, so a distant plant adds to a city's particulate pollution.
What changed
14 Jul 2026New subject
- A study found that 20 of 37 coal plant units within 300 km of Delhi emit sulphur dioxide above the limit, and that the largest share comes from plants exempted from installing the equipment.
Mains: an airshed does not respect city limits, so a programme built city by city cannot fix a regional source.
Graded Response Action Plan
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The Graded Response Action Plan is the set of curbs on vehicles, construction and industry that the Delhi NCR applies in stages as the Air Quality Index worsens through the winter.
What changed
3 Jul 2026New subjectalso in news
- Delhi announced its winter curbs on vehicles and construction five months ahead, to run from 1 November, instead of waiting for the Air Quality Index to cross a threshold.