Why Stubble Burning Worsens Delhi’s Winter Air

In December 2025, Delhi’s air quality index crossed the “severe plus” mark and the Lieutenant Governor issued a public advisory asking vulnerable residents to stay indoors. GRAP Stage III restrictions were back in force, construction sites went quiet, and diesel generators across the city faced fresh scrutiny. What made this particular smog episode strange is that it happened well after the region’s farm fires had all but stopped. Punjab and Haryana had, by the government’s own account to Parliament, recorded a 90 percent drop in stubble-burning incidents that season compared to 2022. If the fires were nearly gone, why was Delhi still gasping?

That question is more useful than the usual finger-pointing at farmers 500 kilometres away, because it forces a look at how stubble burning actually interacts with Delhi’s air, rather than treating it as the single villain of the winter smog story. The honest answer involves both agricultural fires and the city’s own emissions, layered on top of geography and weather that neither farmers nor city planners control. This piece works through that mechanism in detail, using the most recent data available, so the “why” behind the headlines actually holds up.

The Number Everyone Quotes – And Why It Keeps Changing

Ask how much of Delhi’s pollution comes from stubble burning and you’ll get wildly different answers depending on who is asked and when. A Right to Information response from the Central Pollution Control Board, obtained by an environmental activist, put stubble burning’s share of Delhi’s PM2.5 at just 3.5 percent for the October–December window in 2025. That number looks small next to the same source’s figures for earlier years: 13 percent in 2020, 13 percent in 2021, 9 percent in 2022, 11 percent in 2023, and 10.6 percent in 2024. On paper, farm fires appear to be a shrinking problem.

Yet during the same years, forecasting models from IITM’s SAFAR system have reported farm-fire contributions spiking as high as 35–40 percent on specific peak-burning days, particularly right after Diwali when firecracker smoke and stubble smoke arrive together. Both figures are technically correct — they’re just answering different questions. The CPCB’s number is a seasonal average smoothed across roughly three months of data, which mathematically dilutes short, intense pollution spikes. SAFAR’s number captures a single bad day when wind direction, fire count, and local emissions all align badly. A farmer’s smoke plume that pushes Delhi’s AQI from “poor” to “severe” for 48 hours barely moves a three-month average, but it very much moves how the city feels and breathes on those two days.

This is the root of most public confusion on the subject, and it matters because policy built on the wrong version of the number tends to fail. Treating stubble burning as a 3.5 percent afterthought risks ignoring the acute spikes that overwhelm hospitals and schools for days at a stretch; treating it as the primary driver, as headlines often do, risks letting Delhi’s own year-round emissions off the hook entirely. The real picture needs both numbers held at once. (Source: The Tribune, RTI data on 2025 PM2.5 contribution)

The Mechanism: How a Seasonal Add-On Becomes a Trigger

To understand why even a modest addition of smoke can tip Delhi into crisis, it helps to look at what the city’s air is already dealing with before a single field is set alight. Delhi sits inside the Indo-Gangetic Plain, a flat, bowl-shaped stretch of land hemmed in by the Himalayas to the north and the Aravalli hills to the southwest. Those ranges function like walls, blocking the cold, clean air that would otherwise flush the basin and keeping local emissions circulating close to the ground. This geography alone makes Delhi structurally worse off than a coastal or hill city long before winter starts. Our companion piece on why Delhi’s AQI climbs every winter breaks down the full list of contributing sources vehicles, construction dust, industry, and open burning that build this baseline.

Late October brings a second, sharper problem: temperature inversion. As nights turn colder faster than the days, a layer of warm air settles above a layer of cool air near the surface, acting like a lid on a pot. Pollutants that would normally rise and disperse get trapped underneath it instead. Wind speeds drop at the same time, removing the only other mechanism horizontal dispersal that could clear the air. Combine a lid with no fan, and you have a system built to concentrate whatever gets added into it, whether that’s vehicle exhaust, brick-kiln smoke, or paddy straw ash.

This is where stubble burning does its real damage: not as the sole source of Delhi’s pollution, but as a large, fast pulse of particulate matter injected directly into an atmosphere that is already primed to trap it. The smoke also carries moisture and fine ash that act as nucleation points for fog, thickening the visible haze and turning ordinary smoke into the specific type of yellow-grey smog that blankets the region each November. A pollution load that might be manageable in July becomes the tipping point in November purely because the atmosphere has stopped cooperating. It’s the same reason a small kitchen fire fills an entire sealed room with smoke far faster than an open one the physics of containment, not the size of the fire, decides how bad it gets. (Source: AQI.in, Delhi’s geography and pollution trap)

The Three-Week Window That Decides the Season

Satellite fire-count data from Punjab and Haryana consistently shows farm fires clustering in a tight band roughly the last week of October through the first two weeks of November dictated by when combine harvesters finish clearing paddy and how much time farmers have before wheat sowing deadlines. This window almost always overlaps with Diwali, which means firecracker smoke, stubble smoke, and the onset of temperature inversion frequently converge within the same ten-to-fifteen-day stretch. It’s not a coincidence that Delhi’s worst AQI readings of the year, and its recurring appearances on lists of India’s most polluted cities, tend to land inside this exact period rather than being spread evenly across the whole winter.

Even in 2025, with fire counts down 90 percent from 2022, this short window still produced an AQI peak of 428 in November, according to monitoring data compiled by the Centre for Science and Environment. Fewer fires meant a less extreme peak than in years with heavier burning, but the underlying timing pattern fires plus firecrackers plus inversion held. This suggests the calendar itself is a policy lever: enforcement, machine deployment, and public health messaging concentrated specifically on this three-week window would likely deliver more benefit per rupee spent than efforts spread thinly across the entire crop-residue season.

What Happens After the Fires Stop- Delhi’s Own Emissions Take Over

Here is the part of the story that rarely makes headlines. The same CSE analysis that recorded November’s fire-driven peak also tracked what happened in December, once stubble burning had all but ended. Farm-fire contribution to Delhi’s PM2.5 fell to a negligible 0.2 percent that month and yet average PM2.5 concentrations rose by 29 percent, from 163 micrograms per cubic metre in the October–November period to 210 micrograms per cubic metre in December. Neighbouring towns fared worse: Noida saw a 38 percent jump, Baghpat 31 percent. The smoke had left the picture almost entirely, but the smog got thicker anyway.

The explanation lies in Delhi’s own emissions inventory. Local sources account for roughly 35 percent of the city’s total PM2.5 on an average day, and within that local share, transport is the single largest contributor at 46 percent, followed by industrial activity at 22 percent. A further 61 percent of total PM2.5 across the region is “secondary” particulate matter — not released directly as soot, but formed in the atmosphere when gases like nitrogen oxides, sulphur dioxide, and ammonia react with each other, a process that accelerates in the same cold, stagnant conditions that trap stubble smoke. Vehicles, industrial units, and diesel generator sets running through winter power fluctuations all feed this secondary-particle chemistry, which means Delhi’s chronic pollution problem is, at its core, an urban energy and transport problem that simply gets a seasonal boost from agricultural fires rather than being caused by them.

This is also why the Commission for Air Quality Management’s Graded Response Action Plan specifically tightens rules on diesel generator sets operating in Delhi-NCR as AQI worsens DG sets are a controllable slice of that local 46 percent transport-and-power-related emissions share, unlike farm fires hundreds of kilometres away, which fall outside Delhi’s direct jurisdiction entirely. (Source: CSE, “Beyond the Burn” analysis)

The Health Bill Nobody Budgets For

The numbers above translate into something more immediate for anyone living through a Delhi winter: a measurable rise in respiratory illness. A study tracking Delhi’s hospital admissions found that every 10-unit rise in PM2.5 concentration corresponded to roughly seven additional weekly hospital admissions for respiratory disease across the city. Multiply that across a season where PM2.5 regularly sits several hundred units above the WHO’s safe guideline of 15 micrograms per cubic metre as a 24-hour average, and the cumulative burden on emergency departments, pharmacies, and school attendance becomes significant well before anyone develops a diagnosed chronic condition.

Children, the elderly, outdoor workers, traffic police, and anyone with pre-existing asthma, COPD, or cardiovascular disease carry a disproportionate share of this burden. Because Delhi’s elevated AQI period typically stretches from mid-October through January, the exposure isn’t a single bad week — it’s roughly three months of compounding low-grade harm, punctuated by the acute spikes during the stubble-and-firecracker window described earlier. Public health researchers increasingly treat this as a seasonal illness pattern in its own right, comparable to a flu season, rather than an occasional bad-air-day inconvenience. (Source: The Tribune, hospital admissions study)

Why Farmers Keep Burning Despite the Bans

It’s tempting to treat continued stubble burning as simple defiance of the law, but ground-level research from Punjab tells a more complicated story. Farmers typically have just 15 to 20 days between harvesting paddy and the deadline to sow wheat. Combine harvesters, now used almost universally, leave behind loose straw that must be cleared within that window or risk delaying the next crop. Burning remains, in practical terms, the fastest and cheapest way to clear a field, even where it’s illegal.

The alternative crop residue management, or CRM exists but comes with real friction. A Super Seeder or Happy Seeder can cost between ₹1.5 lakh and ₹3 lakh even after a 50 percent government subsidy, and rental rates for these machines with a tractor run ₹1,600 to ₹2,500 per acre, plus another ₹500–800 per acre for attachments like the Super Straw Management System. Research from the Council on Energy, Environment and Water found that 64 percent of farmers avoided the mandated straw-management attachment specifically because of unavailability and cost, and that even among farmers who did adopt in-situ machines, 30 percent still burned part of their field first because full mechanical clearing wasn’t feasible in the time available.

There’s also a seed-variety problem layered underneath the machinery issue. A long-duration, high-yield paddy variety called PUSA 44 was officially withdrawn from sale in October 2023 because it produces nearly two tonnes more excess straw per hectare than shorter-duration alternatives, yet it continues circulating through private seed dealers because farmers still prize its yield. As long as that variety remains in fields, the straw problem it creates persists regardless of how many decomposer sprays or seeder machines are distributed. None of this excuses burning, but it explains why bans and fines alone haven’t ended the practice — the underlying economics of the 15-to-20-day window haven’t actually been solved for a large share of small and marginal farmers. (Source: CEEW, Punjab crop residue management study)

What’s Actually Moving the Needle – And What Isn’t

To be fair to the policy response, some of it has clearly worked. Since 2018-19, the central government has released more than ₹3,120 crore to Punjab and Haryana for CRM machinery ₹1,963 crore to Punjab and ₹1,157 crore to Haryana — funding the distribution of over 260,000 machines and the establishment of more than 33,800 custom hiring centres where smaller farmers can rent equipment they can’t afford to own outright. Combined with wider use of Pusa’s bio-decomposer spray, a low-cost microbial treatment that breaks down stubble in situ without burning, this scale-up is a large part of why fire counts fell 90 percent between 2022 and 2025.

Enforcement has also intensified, with roughly 8,600 FIRs filed against farmers across Punjab and Haryana over a two-year period and nearly ₹60 crore recovered in fines. But the CSE data on December’s pollution spike is a useful reality check on how much credit this campaign should really take for Delhi’s air quality specifically. Existing machine stock over 43,000 Super Seeders and 13,500 Happy Seeders — is already, on paper, sufficient to cover the entire non-basmati paddy area if deployed efficiently, yet adoption gaps persist because of training shortfalls, rental-network informality, and low awareness of digital booking tools like the i-Khet app, which has fewer than 10,000 downloads despite years of promotion. The lesson isn’t that the CRM push has failed — fire counts genuinely dropped but that farm-side fixes alone were never going to solve Delhi’s broader air pollution problem, because most of that problem was never sitting in a Punjab field to begin with.

The Ex-Situ Option That’s Still Stuck in First Gear

Most public discussion of stubble solutions focuses on in-situ machines that keep straw on the field, but there’s a parallel track — ex-situ utilisation, where paddy straw is collected, pelletised, and burned as fuel elsewhere — that has moved far slower than it should have. In 2022, the Finance Ministry mandated that coal-fired thermal power plants co-fire at least 5 percent biomass pellets alongside coal, a step officials said could cut 38 million tonnes of carbon dioxide emissions annually if scaled nationally. Eleven thermal plants ringing Delhi-NCR were specifically directed to adopt this.

By August 2023, only three of those eleven plants had actually increased their biomass share. The rest ran into a supply chain that essentially didn’t exist at the scale required: a shortage of torrefied-pellet manufacturers, inconsistent pellet quality one vendor supplied material with more than double the permitted volatile-matter content — and price quotes running three times the government’s benchmark rate of ₹7 per kilogram. One plant found it could technically manage only 1.5 percent co-firing without capital upgrades that would push up electricity tariffs. In other words, a policy that could have converted a meaningful share of Punjab and Haryana’s excess straw into grid electricity, instead of ash and smoke, stalled on basic industrial logistics rather than farmer behaviour. Fixing that supply chain — reliable pellet manufacturing, consistent quality standards, and pricing that doesn’t undercut the economics for power plants sits entirely outside the farm gate, which is exactly why it tends to get less attention than another round of fines for burning.

What This Means for Delhi-NCR Residents and Businesses This Winter

For individuals, the practical response has to account for both the acute stubble-driven spikes in late October and November and the chronic, locally-driven smog that persists well into January. That means checking AQI readings daily rather than relying on how the sky looks, wearing a properly fitted N95 or N99 mask outdoors on GRAP Stage II days and above, running HEPA air purifiers indoors, and shifting outdoor exercise away from early morning hours when inversion effects are strongest.

For facility managers, industrial units, and anyone operating backup power equipment, the local-emissions half of this story is the more actionable one. Because diesel generator sets sit squarely inside the transport-and-industrial share of Delhi’s own 35 percent local emissions contribution, GRAP stages progressively restrict their use Stage II onward typically bars non-compliant DG sets from operating at all, with fines and equipment sealing for violations, under rules explained in detail in our overview of DG set emission regulations. Fitting a certified retrofit emission control device is currently the most direct way for a generator owner to keep operating through severe-AQI days without falling foul of CAQM enforcement, and it has the added benefit of cutting the very NOx and particulate emissions that feed the secondary-particle chemistry described earlier in this piece. Practical steps for reducing smoke output are covered separately in our guide on cutting visible smoke from diesel generators.

Frequently Asked Questions

Does stubble burning actually cause Delhi’s air pollution?
It’s a genuine contributor, not the sole cause. Stubble smoke acts as a sharp, short-term addition to an airshed that’s already under stress from vehicles, industry, construction dust, and stagnant winter weather. It reliably worsens Delhi’s worst AQI days each year, particularly in late October and early November, but Delhi’s chronic winter smog continues, and often intensifies, well after the fires stop.

What percentage of Delhi’s pollution comes from stubble burning?
Estimates vary by methodology and timeframe. CPCB’s seasonal-average figures put it between 3.5 and 13 percent depending on the year, while SAFAR’s daily models have shown spikes of 35–40 percent on individual peak-burning days, especially around Diwali. Both are accurate representations of different questions average season-long share versus worst-day share.

When does stubble burning season happen in Punjab and Haryana?
The bulk of farm fires cluster in a roughly three-week window from late October through mid-November, driven by the narrow 15–20 day gap farmers have between harvesting paddy and the wheat-sowing deadline.

What is GRAP and how does it connect to stubble burning?
The Graded Response Action Plan is a four-stage emergency framework run by the Commission for Air Quality Management that tightens restrictions — on construction, vehicles, and diesel generators among other sources — as Delhi’s AQI worsens. Stubble-burning season often pushes AQI into the higher GRAP stages, triggering these restrictions even though the rules themselves target local, controllable emission sources rather than the fires directly.

Will Delhi’s air quality improve if stubble burning is eliminated entirely?
It would meaningfully reduce the sharpest pollution spikes of the year, but data from December 2025 when fire contribution fell to near zero yet PM2.5 still rose 29 percent shows that eliminating stubble burning alone would not bring Delhi’s air anywhere close to safe levels. Local transport, industrial, and secondary-particle emissions would still need to be addressed for lasting improvement.

How can residents protect themselves during this period?
Track daily AQI rather than visual haze, use a well-fitted N95/N99 mask outdoors from GRAP Stage II onward, run indoor air purifiers, keep windows closed during inversion hours (typically night and early morning), and postpone outdoor exercise until wind speeds pick up later in the day.

The Bigger Picture

Punjab and Haryana’s farmers cut stubble burning by 90 percent in three years, a genuine policy success that deserves recognition rather than dismissal. And yet Delhi still spent December 2025 under GRAP Stage III with hospitals reporting rising respiratory admissions. Both facts are true at once, and reconciling them is the actual takeaway: stubble burning is a real, measurable trigger that turns a bad air season into a hazardous one during a narrow window each autumn, but it was never the root cause of Delhi’s year-round pollution burden. That burden sits closer to home, in the city’s own vehicles, industries, construction sites, and power backup infrastructure the sources Delhi-NCR actually has direct authority to fix, winter after winter, regardless of what happens in a field 500 kilometres away.