Delhi’s air quality improves to ‘very poor’ after seven days
The average AQI dropped to 308 on Tuesday from 460 on Monday. The level of particulate matter, which had hit the ‘severe+’ zone, also dropped to ‘severe’ levels in the past 24 hours.Updated: Nov 14, 2017 23:59 IST
The National Capital’s air quality improved a little on Tuesday, going back to its pre-Diwali levels. The air quality in Delhi had been hovering in the ‘severe’ category in the last seven days, which is considered as a major health risk.
Weather experts said that Delhiites will now be able to breathe in ‘very poor’ air for some time now, considered normal for this time of the year.
The average AQI dropped to 308 on Tuesday from 460 on Monday. The level of particulate matter, which had hit the ‘severe+’ zone, also dropped to ‘severe’ levels in the past 24 hours.
The last time Delhi witnessed such prolonged spells of severe air quality was in November 2016 when the city faced its worst smog in 17 years. Last November too, the AQI remained 401+ on a scale of 500 for seven straight days. But the severity then was higher with pollution peaking at 497 on the AQI. This year, the highest so far has been 486.
Experts said that weather conditions, which started turning in Delhi’s favour from Sunday, helped bring the improvements.
Pollution levels first entered the ‘severe’ zone on November 7. The AQI hit its peak of 486 on November 9. Thereafter it started improving. The relief, however, was short lived as the air turned foul again from Saturday afternoon. This time the AQI touched 460. But since Sunday it has started improving again.
“The air quality has improved to what it was before Diwali. Such quality of air was last encountered just two days before Diwali. The AQI was 306 on October 17,” said D Saha head of the air quality laboratory of Central Pollution Control Board.
The level of particulate matter – PM10 and PM2.5 – have almost halved from what it was on Sunday afternoon.
Several factors helped in the cleaning up the air. The plummeting mercury condensed the moisture in the air to dew which got deposited on the surface, grass and leaves, in the early morning hours. Some pollutants were removed in this way as they stuck to water droplets.
When the sun’s rays penetrated, they heated up the atmosphere which in turn increased the mixing height allowing the pollutants to disperse at a faster rate.
“The changing wind pattern has helped in the process too. While high altitude winds that usually bring in pollutants from outside have calmed down, the surface level winds that help to flush out local pollutants are gathering speed,” said Gurfan Beig, project director of SAFAR, which operates under the ministry of earth sciences.
The velocity of wind that had dropped to 2km/hr on Saturday shot up to 7km/hr on Tuesday.
First Published: Nov 14, 2017 23:58 IST