NEW DELHI: Delhi's air quality continued to remain in the 'very poor' category for the fourth straight day on Thursday, with forecasts pointing to a possible deterioration to the 'severe' category from Friday, days before Diwali.




The 24-hour average Air Quality Index (AQI) was 369 at 4pm on Thursday, down from 377 recorded at the same time on Wednesday, according to the Central Pollution Control Board (CPCB).




The city's average AQI stood at 350 on Tuesday and 324 on Monday.




Of the 59 active air quality monitoring stations in the national capital, 18 recorded 'severe' air quality. Jahangirpuri reported the highest AQI at 454 at 4 pm, CPCB data showed.




Under CPCB standards, an AQI of 0-50 is categorised as 'good', 51-100 as 'satisfactory', 101-200 as 'moderate', 201-300 as 'poor', 301-400 as 'very poor' and 401-500 as 'severe'.




The Air Quality Early Warning System (AQEWS) has predicted that Delhi's air quality would remain 'very poor' on Thursday before slipping into the 'severe' category from Friday to Sunday.




"The outlook for the subsequent six days is that the air quality is likely to be in the severe to very poor category," the AQEWS bulletin said.




Meanwhile, forecasts by the Decision Support System (DSS) for Air Quality Management in Delhi suggest that stubble burning's contribution to the city's pollution will fall sharply on November 7, while the share of vehicular emissions is expected to increase.




The DSS, which functions under the Ministry of Earth Sciences, estimated that stubble burning accounted for 15.601% of Delhi's pollution on Thursday. Its contribution is projected to rise to 19.201% on Friday before dropping sharply to 1.575% on Saturday.




The DSS projections for stubble burning's contribution to Delhi's PM2.5 levels over the coming days are based on climatological data on fire counts and emissions, rather than real-time farm fire activity.




The share of transport emissions is forecast to rise from 17.913% on Thursday to 18.291% on Friday and 21.108% on Saturday.




Sunil Dahiya, founder and lead analyst at EnviroCatalysts, said the anticipated fall in stubble burning's share was mainly due to changing weather conditions and did not mean that farm fires were declining.




"As a western disturbance moves in, the north-westerly winds that carry smoke from Punjab and Haryana into Delhi are forecast to weaken and turn easterly around Diwali," he said.




Dahiya said Punjab had reported 2,347 farm fires this season, including more than 700 on November 3 and 4 alone.




He said a lower contribution from stubble burning would not necessarily mean cleaner air, as slower winds and morning mist could trap local pollutants from vehicles, industries, waste burning and firecrackers.




He added that the early warning system had already forecast 'severe' air quality for November 6 and 7, and cautioned that pollution from farm fires could return once north-westerly winds resumed.



(With inputs from PTI)