Environment and Disaster Management › Pollution
हिन्दी — Read in HindiAir pollution
The National Clean Air Programme and the sources of polluted air, 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.
Foundation notes: The Graded Response Action Plan · Air quality: the standards and the index
National Clean Air Programme
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The National Clean Air Programme (NCAP), launched in 2019, sets 130 cities, most of them non-attainment cities, a target for one pollutant and pays them to meet it.
- 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).
- Of the money spent by 2026, 68 per cent went on road dust, and little on transport, waste or industry.
- By 2026, 40 cities had not finished source apportionment.
What changed
7 Sep 2026
- Against 2017 to 2018, 108 of the 130 cities had lower annual PM10, 26 cut it by more than 40 per cent and 14 met the standards.
- Of the grants given since 2019 to 2020, 70.5 per cent has been used.
- The Swachh Vayu Survekshan rankings reward effort over results: measured PM10 improvement carries only 2.5 per cent of the weightage.
- Lucknow thus topped the largest cities although its PM10 is more than twice the standard.
Mains: ring fenced funds with penalties for non use, targets aimed at combustion rather than dust, and payments to farmers to diversify crops.
PIB, 7 Sep 2026: India's Path to Blue Skies: From Awareness to Action for Cleaner Air (opens in a new tab) · The Indian Express, 7 Sep 2026: Lucknow's air cleanest, Indore among top 3 in Centre's annual survey (opens in a new tab)
Stubble burning and crop residue management
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Stubble burning is the burning of paddy residue in the fields of Punjab, Haryana and Uttar Pradesh after harvest, in October and November.
Two routes for stubble
In the field
- Incorporated into the soil by machines from custom hiring centres
Outside the field
- Biomass power
- Compressed biogas
- Ethanol
- Pellets
- Co firing in thermal plants
How much it adds, and how it is counted
- It is a modest share of the season's particulate pollution and a large share of it on the worst days.
- Farm fires add no more than 15 per cent of winter particulate pollution, but more than a third on some October and November days.
- How the fires are counted decides how the argument runs.
- Fire counts see active fires during daytime satellite passes, and miss fires lit after the satellites have gone.
- Burnt area maps scorched fields from Sentinel 2 images, and says nothing about how much smoke a fire released.
Why farmers burn, and the alternatives
- Burning is driven by the short gap between paddy harvest and wheat sowing, which short duration paddy and direct seeded rice widen.
- The Crop Residue Management scheme of 2018 funds machines and custom hiring centres in Punjab, Haryana, Uttar Pradesh and Madhya Pradesh.
- Residue can go back into the soil or into a market, as biomass power, compressed biogas, ethanol, pellets or co firing in thermal plants.
What changed
4 Sep 2026
- 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.
The Hindu, 4 Sep 2026: Air quality panel holding talks with Punjab govt. and ISRO over tracking of stubble fires (opens in a new tab) · 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
- 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.
Summer air pollution: PM10 and ozone
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Summer air pollution in India is driven by coarse PM10 and ozone, where winter pollution is dominated by fine PM2.5 trapped by cold, still air.
- Ground level ozone is not emitted directly: it forms when nitrogen oxides and volatile organic compounds react in strong sunlight.
- Heat speeds the reaction that makes it, so a heatwave does not only heat the air: it cooks its pollutants into ozone, which outlasts the heat itself.
- Heat lows produce hot winds that carry West Asian and Thar dust, and thunderstorm downdrafts raise local dust storms (andhi).
- Delhi's Air Quality Early Warning System, set up after the 2018 dust storms, gives multi pollutant forecasts.
Winter versus summer pollution
| Winter | Summer | |
|---|---|---|
| Dominant pollutant | PM2.5 | PM10 and ozone |
| Weather | Cold, still air | Heat lows, hot winds, dust storms |
| Main sources | Combustion and burning | Dust and photochemistry |
| Control | Graded Response Action Plan stages | Dust control and precursor cuts |
What changed
16 Jun 2026New
- The Commission for Air Quality Management (CAQM) revoked winter Graded Response Action Plan (GRAP) curbs in March 2026 but reimposed Stage 1 in April and again in May as summer pollution rose.
- Mumbai, Chennai, Hyderabad, Bengaluru and Kolkata also recorded PM10 and ozone above national standards.
- A study in npj Clean Air found that surface ozone stays high three to four days after a heatwave ends, and attributed over 830 deaths in India in 2024 to heat driven ozone rises, modelled rather than counted.
Mains: Coupled heat and ozone extremes need integrated climate and air quality policy.
The Hindu, 2 Jun 2026: Why do Indian cities get polluted in summer? | Explained (opens in a new tab) · The Hindu, 16 Jun 2026: Heatwaves and ozone together increase India's cardiac deaths: study (opens in a new tab) · The Indian Express, 16 Jun 2026: Heatwaves raise ground-level ozone, worsening health risks: Study (opens in a new tab)
Clean mobility scheme for Delhi NCR trucks and buses
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The clean mobility scheme for Delhi NCR replaces BS IV and older trucks and buses with BS VI or electric vehicles, through the National Capital Region Planning Board.
- Bharat Stage (BS) norms regulate tailpipe nitrogen oxides, carbon monoxide and particulate matter; BS VI tightened limits and added cleaner fuel and onboard diagnostics.
- Older vehicles emit more because worn engines burn fuel incompletely and lack diesel particulate filters and selective catalytic reduction.
- The 2018 source apportionment study by the Automotive Research Association of India (ARAI) and The Energy and Resources Institute (TERI) found transport contributes 14 per cent of PM2.5 in Delhi NCR.
- Trucks and buses are 3 per cent of the fleet but 36 per cent of transport PM2.5.
Who gives what
| Who | What it gives |
|---|---|
| Centre | Interest subvention, fuel vouchers |
| States | Registration fee waiver, motor vehicle tax concession |
| Manufacturers | 8 per cent discount |
What changed
3 Jun 2026New
- The Cabinet approved the scheme for two years; BS III or older vehicles must be scrapped at registered facilities.
- One pre BS heavy vehicle emits as much as 14 BS VI vehicles; a BS IV vehicle emits 2.7 times a BS VI one.
PIB, 3 Jun 2026: Cabinet approves Scheme for support to NCRPB for replacement of old trucks and buses in Delhi-NCR area (opens in a new tab) · The Indian Express, 5 Jun 2026: A new scheme targets Delhi-NCR's older trucks and buses to tackle air pollution. Here's why it matters (opens in a new tab)
Particulate matter and the placenta
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PM2.5 and PM10 can cross the placental barrier and cause oxidative stress and inflammation.
- The inflammation suppresses a protein that keeps the placenta in balance and governs embryo growth, so the placenta invades the uterine wall poorly and forms a weaker nutrient exchange layer.
- Pollution also alters epigenetic switches, so the harm persists after birth.
What changed
2 Jun 2026BriefAn Indian Council of Medical Research (ICMR) funded study by the All India Institute of Medical Sciences (AIIMS) Delhi found Delhi's PM2.5 exposure a significant risk factor for low birth weight. The Hindu, 2 Jun 2026: AIIMS Delhi researchers show exactly how particulate matter affects foetuses (opens in a new tab)
GRAP and Delhi's winter plan, 2026
Copy link to GRAP and Delhi's winter plan, 2026Prelims and Mains
LeadDelhi's winter air: the revised GRAP and a fixed calendar of curbsSeptember 2026
Why in news
On 28 September 2026 CAQM approved a revised GRAP schedule, and Delhi announced a winter plan with curbs fixed by date from 1 November 2026 to 31 January 2027.
Background
- GRAP has four stages tied to the Air Quality Index: Stage I at 201 to 300 (poor), Stage II at 301 to 400 (very poor), Stage III at 401 to 450 (severe) and Stage IV above 450 (severe plus).
- Each stage adds to the one below, and a stage can be invoked on a forecast, before the reading crosses its band.
- In winter, falling temperatures trap vehicle exhaust, industrial emissions and crop residue smoke close to the ground.
What changed in GRAP
- Curbs on diesel generator sets and on the entry of buses of BS IV and below moved up from Stage II to Stage I.
- The exemption for goods vehicles of BS IV and below carrying essential commodities in Stages III and IV was removed.
- Dust monitoring of construction sites was extended beyond municipal limits to industrial and highway corridor zones.
Delhi's fixed calendar
- From 1 November to 31 January dust generating construction stops, parking charges double, offices stagger their hours and up to half the staff work from home.
- All construction and demolition is banned from 10 December to 20 January.
- From 1 November vehicles below BS VI registered outside Delhi are barred, with compressed natural gas and electric vehicles exempt.
- From 1 October a vehicle without a valid Pollution Under Control Certificate gets no fuel in the region.
The farm fire side
- CAQM has directed Punjab, Haryana and Uttar Pradesh to eliminate paddy stubble burning in 2026.
- A strong El Niño is expected to bring fewer rain bearing Western Disturbances, so the air will clear less often this winter.
GRAP stages, as revised in September 2026
| Stage | Air Quality Index | Air quality | Actions |
|---|---|---|---|
| I | 201 to 300 | poor | 25 |
| II | 301 to 400 | very poor | 8 |
| III | 401 to 450 | severe | 10 |
| IV | above 450 | severe plus | 5 |
The way forward
- A fixed calendar gives residents and businesses notice, which graded curbs never did, but it treats the season and not the sources.
- Vehicles are the largest primary source of Delhi's winter pollution, at about 23 per cent, so cleaner transport matters more than seasonal bans.
- Municipal and even regional boundaries are too small for the problem, which is the case for managing the whole airshed.
Prelims facts
- GRAP stages follow the Air Quality Index: 201, 301, 401 and above 450.
- CAQM is a statutory body and acts through directions that the States must enforce.
- The airshed approach manages air quality across a shared geographic area and not within administrative boundaries.
- BS VI norms, in force nationwide since 2020, set stricter limits on nitrogen oxides and particulate matter.
The Graded Response Action Plan (GRAP) is the set of emergency curbs for Delhi and the National Capital Region that switch on in four stages as the Air Quality Index worsens.
- It is run by the Commission for Air Quality Management (CAQM), a statutory body under an Act of 2021.
- Its curbs arrive only when the air has already turned bad, so Delhi has added a winter plan that fixes restrictions by calendar date.