Delhi recorded its worst air quality on Diwali eve in a decade on Saturday, with the 24-hour average Air Quality Index reaching 369 in the very poor category.

Central Pollution Control Board data showed the reading surpassed previous years, including 296 in 2025, 307 in 2024, and 220 in 2023. The last higher pre-Diwali figure came in 2016 at 404.

The deterioration stemmed from a combination of local emissions, peak stubble burning in neighboring states, and calm winds that trapped pollutants. Stubble-burning incidents in Punjab and Haryana hit seasonal highs on Saturday, according to satellite data.

On Sunday, Diwali day itself, the average AQI climbed to 376, with multiple stations crossing into the severe range above 400. Jahangirpuri recorded the highest at 463, while other areas like Punjabi Bagh and RK Puram also exceeded 440.

Authorities have kept Stage III of the Graded Response Action Plan in effect across Delhi-NCR. The measures include restrictions on construction, industrial operations, and vehicle use in an effort to curb further spikes.

Experts from the System of Air Quality and Weather Forecasting and Research warned that conditions favor even higher pollution on Monday, with north-northwesterly winds expected to carry additional smoke from farm fires. The Air Quality Early Warning System projected severe levels persisting for several days after the festival.

Delhi has long struggled with winter pollution spikes driven by firecracker use, vehicle emissions, and regional agricultural practices. This year's pre-Diwali peak highlights ongoing challenges despite enforcement efforts and green cracker permissions limited to specific windows.