A new satellite-based study has found that the notorious November smog choking Delhi cannot be blamed on any single source, with most of the pollution originating from outside the city and trapped by stagnant winter weather.
The "Delhi Smog Atlas," released by Uday GeoAnalytics Consultancy (UGAC), combined satellite data, 63 ground monitors, and weather models to trace the capital's polluted air to ten distinct causes. The study period, from November 1 to 10, 2026, recorded an average PM2.5 level of 207 µg/m³, which is about 3.5 times India's daily limit of 60.
"Every winter the debate picks one culprit, whether it is stubble, traffic or firecrackers. The data shows all of them adding to the same air, trapped by the same weather," said Aditya Jha of UGAC, in a statement accompanying the report. "Delhi cannot fix this alone, and no single ban will fix it."
A Regional Problem Trapped by Weather
The study highlights that a majority of Delhi's winter PM2.5 comes from outside its borders. It cites a TERI-ARAI source study finding that only about 36% of the city's winter PM2.5 comes from its own emissions. A key factor is the weather. The Atlas found that on nine of the ten study days, poor ventilation trapped pollutants close to the ground. On Diwali, November 8, the ventilation index was at its lowest, contributing to the city's worst air quality on that day since 2021, with an average AQI of 376.
The report points to secondary particles—formed in the atmosphere from coal-fired SO2, vehicular NOx, and agricultural ammonia—as the largest single contributor, making up about 32% of winter PM2.5, according to a real-time study for the Delhi Pollution Control Committee.
Coal Plants and Farm Fires Under Scrutiny
The Atlas used satellite data to identify a clear nitrogen dioxide plume over 16 of the 18 coal plants within 320 kilometers of Delhi. It cites estimates that these plants emitted about 154 kilotonnes of SO2 in 2025, with 81% coming from plants that no longer have to install sulphur scrubbers after rules were relaxed in July 2025.
While the study found a 94% reduction in farm fires in India's Punjab compared to 2020, it noted that smog levels remained severe. It also pointed to fires across the border in Pakistan's Punjab, which increased in the same period, with 71% of air paths traced backwards from Delhi coming from the north-west. However, citing research from CREA, the Atlas noted that crop fires only account for an average of 4.9% of Delhi's PM2.5 during the October-November period.
The Sources Delhi Can Control
The report also quantified the impact of local sources. It found that 16,900 heavy trucks enter the city daily, contributing 23% of transport emissions. On Diwali night, between 7 p.m. and 3 a.m., PM2.5 levels were higher than on ordinary nights at 56 of 63 monitors, with a 407% spike recorded at Sector-1 in Noida. The study also noted that 1.14 crore people live within 500 meters of a major road, and 24 lakh within two kilometers of a landfill, with NO2 levels weighted by population being 13% above the area average.
Solutions Must Be Regional and Long-Term
The report suggests that quick fixes have not worked. Citing the National Clean Air Programme, it notes that while Delhi's PM10 fell about 17% between 2017-18 and 2025-26 against a 40% target, measures like smog towers, cloud-seeding trials, and the odd-even traffic scheme have shown little to no measurable benefit.
The measures with the strongest record, the report states, cut pollution at the source, such as the shift to CNG and electric buses, the ban on coal for NCR industry, and cleaner brick kilns. It concludes by citing the World Bank's finding that a plan shared across the entire Indo-Gangetic Plain is the most cost-effective way forward.
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