Despite strong winds, why is Delhi’s air quality on the slide?

According to the Central Pollution Control Board’s daily bulletin, Delhi registered an AQI value of 208, which places it in the ‘poor’ zone.
By HT Correspondent | Hindustan Times, New Delhi
UPDATED ON OCT 09, 2020 03:35 AM IST
Birds fly over the heavily polluted waters of the Yamuna River, at Kalindi Kunj in New Delhi, India, on Thursday, October 8, 2020.(Biplov Bhuyan/HT photo)

Despite the average wind speed of 15-16 kmph, air quality in Delhi continued to be poor on Thursday for the second consecutive day. According to the Central Pollution Control Board’s daily bulletin, Delhi registered an AQI value of 208, which places it in the ‘poor’ zone.

Experts said though faster winds play a major role in the dispersion of pollutants, it is not helping in case of Delhi since the wind speed is not consistent throughout the day. As well as the direction of wind is not helpful since it is blowing from the northwest bringing in particulate matter (PM2.5 and PM10 -- one of the primary pollutants in Delhi’s air) from Haryana and Punjab where farm fires are raging, they said.

According to scientists at the India Meteorological Department (IMD), the wind speed reduces between evening and early morning hours. They also said that currently the northwesterly winds are bringing in fumes from crop stubble burning in Haryana and Punjab, which according to the Delhi government is one of the major contributors of particulate matter to Delhi’s air.

“These pollutants are not being able to disperse as much just with the day wind, as the winds turn calm from evening to early morning hours. The duration for which the wind speed is good is very short. Besides, with a dip in mercury, the ventilation index (the ability of the atmosphere to dilute and disperse the pollutants over a region) has also become slightly low,” said Kuldeep Srivastava, head of IMD’s regional weather forecasting centre.

On Wednesday, Delhi’s air plunged into the ‘poor’ zone for the first time since June 28. Government agencies have warned that the air quality in Delhi may deteriorate further over the next two days though remaining in the ‘poor’ zone. According to CPCB, prolonged exposure to poor air may lead to breathing discomfort to most people.

As per the System of Air Quality and Weather Forecasting and Research (Safar), the central government’s air quality monitoring and forecasting wing, PM 2.5 being the lead pollutant is characteristic of winter. “The forecast for AQI is in the higher end of moderate to the poor category on Friday. However, it is predicted to improve thereafter to be back in the moderate category. A gradual increase in stubble burning fires was observed on Wednesday around Punjab, Haryana, and neighbouring border regions. The boundary layer wind direction and speed are favourable for the transport of pollutants towards Delhi at present, but a shift in the wind direction is likely from October 11, which is likely to help improve air quality,” the Safar bulletin stated.

As per Safar, the fire count in the northwest region on October 7 was 399.

IMD’s Srivastava also said that wind speed in the region is likely to improve by Sunday.

“The air quality may improve slightly on October 11-12 because of probable thunderous developments in the region. The wind direction will also change to southeasterly during this time. However, this pattern will change from October 15, with a return of northwesterlies and a dip in both night and day temperatures,” said Srivastava.

On Thursday, the minimum temperature settled at 19.1 degrees Celsius, two notches below normal while the maximum settled at 35.6 degrees, two notches above normal.

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