Delhi continued to be engulfed in a thick layer of smog since the weekend on December 15. Airlines, including IndiGo and Air India, cancelled flights across Delhi, Mumbai, Indore, Lucknow, Varanasi, Coimbatore, and Kolkata, due to low visibility. Indigo cancelled 109 flights, and Air India scrubbed 37 of its operations. Delhi's average Air Quality Index (AQI) is at 498, which falls under the 'severe category'. 38 out of 40 air quality monitoring stations recorded 'severe' air quality. The Central Pollution Control Board (CPCB) classifies 401 to 500 AQI as ‘severe’.