Strong, sustained winds swept through Delhi, rapidly dispersing dense smoke layer and bringing AQI down to 339 by 4pm Friday, further improving to 323 by 7pm.

Delhi’s air quality has been the second cleanest post-Diwali since 2015, maintaining a “very poor” Air Quality Index (AQI) instead of deteriorating to “severe”. This stability is credited to “strong wind ventilation”, with speeds reaching 16 kilometres per hour.

While the 24-hour air quality index (AQI) climbed steadily through Thursday night — from 328 in the early evening to 338 at midnight, reaching 362 by 9am Friday — the city experienced an unexpected respite. Strong, sustained winds swept through Delhi, rapidly dispersing the dense smoke layer and bringing the AQI down to 339 by 4pm Friday, further improving to 323 by 7pm.

The use of fireworks, an increase in stubble burning, and emissions from various local sources that release toxic gases pushed the city’s air quality into the upper range of “very poor” late Thursday night and into Friday morning.

Mahesh Palawat, vice president at Skymet meteorology, explained this complex interaction between temperature and pollution: “Higher temperature keeps mixing height high and allows pollutants to move and disperse freely. Low temperature slows down wind speed and also traps pollutants closer to the surface through a phenomena called inversion.”

He noted that while winter months typically see the mixing height drop to a mere 200-300 metres, Thursday maintained mixing height of 2,100 metres.