New Delhi, Dec 28 (PTI) Delhi’s air quality showed a slight improvement Friday as it recorded ‘very poor’ pollution level, but remained on the brink of turning ‘severe’ due to drop in temperature which is slowing dispersion of pollutants, authorities said.

The Central Pollution Control Board data showed the overall air quality index (AQI) at the ‘very poor’ level of 394, while the Centre-run System of Air Quality and Weather Forecasting (SAFAR) showed an AQI of 372, which falls in the ‘very poor’ category.

The air quality slipped to the ‘severe’ category Thursday before slightly improving Friday, but it remained on the brink of turning ‘severe’ again, authorities said.

According to CPCB data, 11 areas recorded severe pollution, while 24 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 241 and the PM10 level at 376 in Delhi, the 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. There was a slight drop in the pollution level and the air quality moved to the ‘very poor’ category Wednesday.

On Thursday, the air quality again worsened and turned ‘severe’.

According to the Indian Institute of Tropical Meteorology, the ventilation index is marginally favourable for dispersion of pollutants at 5,000 sqm/second.

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 the System of Air Quality and Weather Forecasting and Research, the air quality over Delhi has deteriorated slightly and touched upper side of the ‘very poor’ category.

“However, now wind speed has picked up slightly which may lead to slight improvement in the pollution level from evening until tomorrow. Since moderate cold wave to severe cold wave conditions are prevailing over major parts of north india surrounding Delhi, appreciable improvement is not expected,” it said.

“Such adverse weather is the major reason for the sustained pollutant levels in the very poor range. The AQI will continue to remain in the ‘very poor’ category (340-370) in the next three days and overall mass concentration of PM2.5 will hover around 200 g/m3 and will not cross 250 g/m3,” it said.

This is published unedited from the PTI feed.