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Thursday, December 02, 2021

Delhi: AQI ‘very poor’ again, slight relief over next 2 days

From November 24 onwards, however, a drop in temperature and a fall in local wind speed could make the dispersion of pollutants difficult.

By: Express News Service | New Delhi |
Updated: November 22, 2021 11:06:27 am
Foggy conditions are likely to persist all week. The relative humidity at 8.30 a.m. was 93%, while the temperature at the same time was 13.2 degree Celsius.

Delhi’s air quality remained in the ‘very poor’ category on Sunday, with an AQI of 349 according to the Central Pollution Control Board bulletin. This was only marginally better than the 374 recorded on Saturday.

Stronger winds are supposed to have aided the dispersion of pollutants. According to scientists at the India Meteorological Department, wind speed picked up on Sunday, reaching 15 to 20 kmph between 11 am and 1 pm.

Data from the Delhi Pollution Control Committee (DPCC) shows particulate matter levels fell with a marginal increase in wind speed in the afternoon at some stations. At the Jawaharlal Nehru Stadium monitoring station, wind speed increased from 1.6 m/s at 8 am to 4.9 m/s at 1 pm, but fell again to around 1.7 m/s at 8 pm. Simultaneously, PM 2.5 levels fell from 266 µg/m3 at 8 am to 88 µg/m3 at 1 pm, and increased again to 144 µg/m3 at 8 pm.

PM 10 levels at Anand Vihar fell from a high of 744 µg/m3 at 8 am to 202 µg/m3 at 1 pm, but climbed again to 587 µg/m3 at 7 pm. Wind speed picked up marginally at the station around noon, from 0.5 m/s at 10 am to 1 m/s at 2 pm, but fell again to around 0.3 m/s at 4 pm.

The SAFAR forecasting system suggests that winds from the northwest of Delhi are likely to become stronger from Sunday night till November 23. Local wind speed is also likely to be high, and this combined with a fall in stubble burning instances indicate that the air quality could improve, but is likely to stay in the lower end of the ‘very poor’ category for the next two days, the forecast said.

From November 24 onwards, however, a drop in temperature and a fall in local wind speed could make the dispersion of pollutants difficult.

The farm fire count, according to the SAFAR system, fell to 181 on Sunday and the contribution of stubble burning to PM 2.5 levels in Delhi was around 8 per cent.

The 24-hour average AQI at some monitoring stations, which had remained in the ‘severe’ category Sunday morning, had improved to ‘very poor’ by 8 pm. At the Anand Vihar monitoring station, the AQI as a 24-hour average was 429 on Sunday morning and had fallen to an average of 394 by 8 pm. The monitoring station at R K Puram recorded an average AQI of 407 in the morning, which improved to reach a 24-hour average of 359 by 8 pm.

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