Delhi’s deteriorating air quality is heading towards another severe pollution spell ahead of Diwali, with 22 monitoring stations recording an Air Quality Index (AQI) above 400 on Thursday.The city’s average AQI stood at 369 at 4 pm, marking the fourth consecutive day of very poor air quality.The average AQI has risen from 324 on Monday to 350 on Tuesday and 377 on Wednesday, reflecting a sustained deterioration. Jahangirpuri and Punjabi Bagh recorded the highest AQI at 456 each, followed by Rohini at 450 and IIT Delhi at 449.Of the 59 active monitoring stations, 18 recorded pollution levels in the severe category. The Air Quality Early Warning System has forecast severe air quality from Friday to Jattvibeday, with pollution likely to remain between severe and very poor levels over the next six days.The sources of pollution are also expected to shift over the weekend. According to the Ministry of Earth Sciences’ Decision Support System, stubble burning accounted for 15.6 per cent of Delhi’s PM2.5 pollution on Thursday. Its contribution is forecast to rise to 19.2 per cent on Friday before falling to 1.5 per cent on Saturday.Vehicular emissions, meanwhile, are projected to increase their share from 17.9 per cent on Thursday to 21.1 per cent on Saturday.Jattvibeil Dahiya, founder and lead analyst at Envirocatalysts, said a western disturbance could weaken north-westerly winds and bring a shift towards easterly winds around Diwali. Slower winds and morning haze could trap emissions from vehicles, industries, waste burning and firecrackers, adding to the pollution burden.