Low temp, poor wind speed push Delhi’s air quality back in ‘very poor’ zone

The national Capital recorded its coldest day of the season on Wednesday with the minimum temperature being recorded at 9.2 degrees Celsius, and the wind speed stayed in the range of 5-10km/hr, according to IMD data
The 4pm average air quality index in Delhi was recorded at 361 on Wednesday, compared to 290 on Tuesday even as the forecasting agencies said that similar meteorological conditions over the next two days may keep the air in the very poor zone. (AP)
The 4pm average air quality index in Delhi was recorded at 361 on Wednesday, compared to 290 on Tuesday even as the forecasting agencies said that similar meteorological conditions over the next two days may keep the air in the very poor zone. (AP)
Published on Nov 25, 2021 12:29 AM IST
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A combination of low temperature and poor wind speed pushed Delhi’s air quality back into the ‘very poor’ category on Wednesday, a day after being recorded in the poor zone -- the best since November 1, scientists said.

The national Capital recorded its coldest day of the season on Wednesday with the minimum temperature being recorded at 9.2 degrees Celsius, and the wind speed stayed in the range of 5-10km/hr, according to IMD data.

The 4pm average air quality index in Delhi was recorded at 361 on Wednesday, compared to 290 on Tuesday even as the forecasting agencies said that similar meteorological conditions over the next two days may keep the air in the very poor zone. They said wind speed is expected to pick up November 27 onwards that will help disperse pollutants and improve air quality.

Gufran Beig, founder and project director at the System of Air Quality and Weather Forecasting And Research (Safar), said wind speed is expected to remain below 5 km/hr for the next two days. “We are experiencing calm wind conditions, and from Thursday, it may further drop to 3-4 km/hr. This will lead to pollutants accumulating over Delhi and air quality will go up to the higher end of the ‘very poor’ category (AQI value 300-400).”

According to Safar, the contribution of farm fires to Delhi’s PM 2.5 levels on Wednesday was just 2% , with 432 incidences of stubble burning recorded in the northern plains. According to the Safar bulletin, local weather will now play a key role in determining air quality. “With the onset of winter, local weather is likely to be dominating factor in determining air quality,” the bulletin said.

IMD scientist RK Jenamani said though wind speeds on Wednesday were recorded in the range of 5-10 km/hr, it was calmer in the early hours of the day. “At night, and in the morning, wind speed will be calm over the next two days,” he said.

The Early Warning System (EWS) for Delhi, another forecasting mechanism under the ministry of earth sciences, said shallow fog will start occurring over Delhi in the morning hours.

“The predominant surface wind is likely to be coming from southeast/southwest direction, with wind speeds ranging between 5-8 km/hr. They will remain calm during evening and night, with shallow fog occurring in the morning on both Thursday and Friday,” it said.

Dipankar Saha, former head at the Central Pollution Control Board’s air laboratory, said while stubble burning impacts Delhi’s air largely between October 15 and November 15, December and January generally see a deterioration in air quality due to meteorological factors such as low temperature, fog and low wind speed. “Wind, along with low temperatures, will play a key role now. We may also start seeing the impact of fog in the morning hours,” he said.

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Wednesday, December 01, 2021