NEW DELHI: Stubble burning, along with adverse meteorological conditions, kept the citys air quality in the severe category with the average air quality index (AQI) at 419 on Thursday. A thick layer of haze appeared over the city with the visibility dropping to 200 metres in the early hours and improving to only 700 metres around 4pm.Meanwhile, the Central Pollution Control Board (CPCB) stated that there was an error in calculating the AQI at 4pm on Wednesday and the revised index was 398, in the very poor category, and not severe 401.The AQI script did not capture the data of four out of the 35 operating stations on Wednesday and, hence, the reading was revised, CPCB clarified.Track the pollution level in your cityOn Thursday, AQI in Faridabad was severe at 424, while it was very poor in Ghaziabad (376), Gurgaon (363), Noida (355) and Greater Noida (340).Satellites on Thursday detected 1,271 farm fires in Punjab, 46 in Haryana and 56 in Uttar Pradesh. The Decision Support System, a central forecasting body, estimated the share of biomass burning in Delhis PM2.5 at 7.6% on Thursday morning. However, the real-time source apportionment study by IIT-Kanpur put the contribution at 28%. CPCBs data shows that AQI has been witnessing a sharp rise since Thursday morning. It stood at 393 in the upper end of the very poor category at 9am and entered the "severe" zone at 1am with a reading of 406. While the 24-hour average AQI released by CPCB at 4pm was 419, the air quality deteriorated further in the evening and reached 435 at 8pm.The air quality of the capital is likely to remain very poor from Friday to Sunday, according to Air Quality Early Warning System for Delhi, the forecasting body under the Union ministry of earth sciences. Since the northwesterly winds blew on Thursday, the wind direction was favourable for the transport of smoke from the burning sites to Delhi. The city has been recording low temperatures, which slow down the process of pollution dispersion. The minimum temperature was 11.3 degrees Celsius, two degrees below normal at base station Safdarjung. Calm winds prevailed in the city, also leading to the accumulation of pollutants."From Wednesday evening to Thursday night, the wind speed was nil at Safdarjung. While Palam saw calm winds in the early morning hours and evening, light winds up to 6kmph blew for a few hours during the day," said Kuldeep Srivastava, head of the Regional Weather Forecasting Centre, India Meteorological Department. Similar meteorological conditions are likely to prevail in the city for the next two-three days, he added.

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