Delhi's Winter Smog and Stubble Burning

Last updated May 29, 2026 · 7 min read

Every year, as autumn turns to winter, Delhi's air quality collapses into one of the world's most severe recurring pollution events. The National Air Quality Index routinely reads "Severe" (above 400) and, on the worst days, runs off the 0–500 scale entirely. This guide explains the ingredients of the crisis, why it recurs, and how to read the numbers.

The ingredients

Delhi's winter smog is a stack of overlapping causes that peak together:

• Stubble burning. After the autumn rice harvest in Punjab and Haryana, farmers have a short window to clear paddy residue before sowing wheat. Burning is the cheapest, fastest method. Satellite fire counts spike in October–November, and on peak days the smoke transported to Delhi can account for a large share of the city's PM2.5.
• Diwali fireworks. The festival falls in this same window; firework smoke produces a sharp overnight PM2.5 spike layered on top of the agricultural smoke.
• Winter meteorology. Falling temperatures, calm winds, and temperature inversions trap pollution near the ground instead of dispersing it.
• Year-round baseline. Vehicle exhaust, industry, construction dust, and biomass burning provide a high baseline that the seasonal sources build on.

Why it recurs — the economics of the burn

The burning is hard to stop because the incentives are stubborn. Combine harvesters leave tall residue that is costly to clear by other means, and the window between rice harvest and wheat sowing is tight. A groundwater-conservation law that delays rice transplanting also pushes the harvest — and therefore the burning — later into the autumn, when winds are calmer and the smoke disperses less. Alternatives like the "Happy Seeder" and residue-management subsidies exist but adoption has been uneven.

The policy response

Delhi-NCR has an escalating playbook. The Graded Response Action Plan (GRAP) triggers measures as AQI worsens — restrictions on construction and certain vehicles, brick-kiln and diesel-generator curbs, and at the most severe stage, school closures and entry bans on trucks. The odd-even scheme rations private cars by licence-plate parity on the worst days. A dedicated Commission for Air Quality Management now coordinates the regional response.

Reading the National AQI when it's "Severe"

India's AQI shares the 0–500 range with the US AQI but spaces its categories very differently — an Indian AQI of 200 is far worse air than a US AQI of 200. During the winter peak, the driver is almost always PM2.5. The CPCB portal and SAFAR publish station-level readings and forecasts, including SAFAR's estimate of the stubble-smoke share. See our National AQI guide for how the categories map.

What residents do

• Track PM2.5 directly, not just the category — on "Severe" days the number behind the label matters.
• Run indoor air purifiers sized for the room, and seal gaps; indoor PM2.5 tracks outdoor closely without filtration.
• Wear a fitted N95 outdoors during peak episodes.
• Shift exertion to cleaner hours and watch the forecast — the worst smog often clears slightly with afternoon mixing.

Primary sources: CPCB — National Air Quality Index · SAFAR (Ministry of Earth Sciences)