Delhi experienced its worst December air quality since 2018, with an average Air Quality Index (AQI) of 349. The city recorded 'severe' air quality on five days this month. Official data indicates that farm fires contributed only 3.5% to PM2.5 pollution until December 5th, despite Delhi-NCR remaining highly polluted. The Central Pollution Control Board (CPCB) relies on a 2018 study for source apportionment, with no comprehensive update since then.