Delhi's air quality was on the brink of turning severe again with unfavourable meteorological conditions like low wind speed preventing dispersion of pollutants on Thursday, authorities said.
The Central Pollution Control Board data showed the overall air quality index (AQI) at the 'very poor' level of 395, while the Centre-run System of Air Quality and Weather Forecasting (SAFAR) showed an AQI of 372, which too falls in the 'very poor' category.
According to CPCB data, 17 areas recorded severe pollution, while 15 areas witnessed 'very poor' air quality.
In NCR, Ghaziabad recorded severe air quality while Faridabad, Gurgaon and Noida recorded 'very poor' air quality.
The overall PM2.5 level fine particulate matter in the air with a diameter of less than 2.5 micrometer was recorded at 296 and the PM10 level at 453 in Delhi, CPCB said.
The national capital recorded its second highest pollution level of the year Sunday with an AQI of 450. The air quality remained 'severe' Monday and Tuesday before moving to the 'very poor' category on Wednesday.
On Thursday, the air quality again worsened and was on the verge of turning severe by remaining just points below the very poor category.
According to the Indian Institute of Tropical Meteorology, the air quality is likely to deteriorate on Thursday but improve marginally on Friday.
The ventilation index is marginally favourable for dispersion of pollutants at 4,500 sqm/second, IITM said.
The ventilation index is the speed at which pollutants can disperse. A ventilation index lower than 6,000 sqm/second, with average wind speed less than 10 kmph, is unfavourable for dispersion of pollutants.
According to SAFAR, the overall air quality in Delhi is very poor.
"It is likely to increase tomorrow by a few notches but will continue to remain in very poor category in next 3 days. Major reason for predicted increase is a decline in surface wind speed which will disperse pollutants slowly unlike yesterday. Other meteorological factors are also not very favourable," SAFAR said.