Delhi's air quality improved to the 'poor' category on Sunday, with the Air Quality Index (AQI) settling at 290 at 4 pm, offering some respite after several days of 'very poor' pollution levels that had kept the national capital shrouded in smog following Diwali.
According to a PTI report, Of the 58 air quality monitoring stations in the city, 34 recorded 'poor' air quality, 23 reported 'very poor' levels and one, Delhi Cantonment, registered 'moderate' air quality. NSIT Dwarka recorded the highest pollution level, with an AQI of 364.
Earlier in the morning, Delhi's air quality remained in the 'very poor' category, with an AQI of 350, according to the Sameer app, reported PTI.
The improvement marked the first time since November 10 that the city's AQI had fallen into the 'poor' category. It had last recorded an AQI of 299 on November 10, while the reading stood at 261 on November 1.
Delhi's air quality had remained in the 'very poor' category since November 11, with several hourly readings approaching the 'severe' threshold and crossing it once.
According to real-time source apportionment estimates by the Air Quality Early Warning System and the Integrated Decision Support System, biomass burning was the largest contributor to Delhi's pollution on Sunday, accounting for 37.1 per cent. This category includes stubble burning, domestic solid biofuel use and the burning of dung cakes and wood.
Secondary organic aerosols, which are fine particles formed in the atmosphere through chemical reactions involving gases, were the second-largest contributor at 22 per cent. Vehicular emissions accounted for 17.2 per cent, followed by secondary inorganic aerosols at 9.6 per cent.
Waste burning, including municipal waste and materials containing plastic and rubber, contributed 5.5 per cent, while mixed combustion accounted for 4.3 per cent. Mineral dust and ash contributed 2 per cent, firecrackers 1.6 per cent and industrial emissions 0.6 per cent.
The Air Quality Early Warning System has forecast that Delhi's air quality is likely to remain in the 'poor' category on November 16 before deteriorating to 'very poor' from November 17 to 18. The city is likely to continue experiencing 'very poor' air quality over the following six days, it said.
Weather experts attributed Sunday's improvement to stronger winds and light rainfall, which helped disperse pollutants.
According to the India Meteorological Department (IMD), very light rain or drizzle was recorded at several places in Delhi during the preceding 24 hours, with surface wind speeds reaching up to 15 kmph from the southwest.
Generally cloudy skies, turning partly cloudy towards the afternoon, prevailed over the national capital on Sunday. Surface winds reached speeds of up to 10 kmph from the southwest, the weather department said.
The IMD's forecast bulletin also indicated a decline in Delhi's ventilation index from 16,000 square metres per second on November 15 to 15,000 on November 16, 7,500 on November 17 and 6,000 on November 18.
A ventilation index below 6,000 square metres per second, combined with an average wind speed of less than 10 kmph, is considered unfavourable for the dispersion of pollutants, the bulletin said.
The Central Pollution Control Board (CPCB) classifies AQI readings between zero and 50 as 'good', 51 and 100 as 'satisfactory', 101 and 200 as 'moderate', 201 and 300 as 'poor', 301 and 400 as 'very poor', and 401 and 500 as 'severe'.
(With inputs from PTI)