Explained: If stubble burning dropped this year, why did Delhi’s pollution still spike after Diwali?

New Delhi: Delhi’s post-Diwali air turned severely toxic this year even as stubble burning incidents in Punjab and Haryana declined by 77.5 per cent during the first half of October. This marks the sharpest fall in farm fires in five years — yet the Capital recorded its highest post-Diwali PM2.5 levels in recent times. So what explains this paradox?According to data from the Indian Agricultural Research Institute (IARI), only 175 stubble burning cases were reported in Punjab and Haryana between October 1 and 12, 2025, down from 779 in the same period in 2024. Despite this, Delhi’s PM2.5 levels rose from a pre-Diwali average of 156 µg/m³ to 488 µg/m³ after Diwali, a three-fold spike.For the first time, the trend indicates that local emissions, not farm fires, were the primary reason behind Delhi’s post-festival pollution surge.Yes. Heavy rainfall and flooding during the late monsoon in Punjab and Haryana delayed paddy harvesting, reducing agricultural residue burning during early October. This led to a cleaner start to the winter season for Delhi, with PM2.5 15.5 per cent lower than the same period in 2024.However, the improvement was short-lived.Meteorological data from the India Meteorological Department (IMD) reveals that Delhi experienced a drop in nighttime temperatures to nearly 19°C, combined with low wind speed (below 1 m/s). This created a temperature inversion — a condition where pollutants are trapped close to the ground due to stagnant air.Firecracker emissions added to existing urban pollution sources such as vehicular emissions, biomass burning and construction dust, leading to a rapid buildup.“High concentration of PM2.5 is due to local emission of firecrackers. Wind speed is below 1 metre per second, hence there is no chance of pollutants being transported from other regions,” said Dr S.K. Dhaka, Professor, University of Delhi.Historically, farm fires accounted for up to 40 per cent of Delhi’s pollution during late October and November. This year, satellite data shows those fires were not active during the Diwali period. The timing of the festival, occurring before peak burning season, further reduced the impact of agricultural burning.However, cleaner air from reduced stubble burning did not translate into better air quality — since local sources are now driving pollution trends.The Delhi government and the Commission for Air Quality Management (CAQM) have focused heavily on crop burning as the main contributor to air pollution. But the 2025 data suggests that urban emissions — particularly firecracker usage and vehicular pollution — have emerged as the dominant factors.Experts say the policy focus may now need to shift:“Stubble burning numbers have fallen substantially, but local emissions remain largely unregulated,” said Palak Balyan, Research Lead at Climate Trends. “The current air emergency cannot be solved without addressing transport and construction, which now contribute more consistently than agricultural fires.”The second half of October and early November are expected to see a rise in farm fires as harvesting picks up. With the wind direction shifting northwestwards, Delhi could experience another spike in air pollution.

But the key takeaway from this year’s data is clear — even if stubble burning is reduced, Delhi's air quality cannot improve without tackling local sources of emissions.