The national capital's air oscillated between 'very poor' and 'severe' on Nov 2
After ‘severe plus’ on November 1, 2019, Delhi’s air quality improved marginally but continued to oscillate between ‘severe’ and ‘very poor’ on November 2. The improvement could be attributed to a slight increase in wind speed.
It was recorded at around 11 kilometres per hour late afternoon. The 24-hour average air quality index (AQI) of the city was 399 — just on verge of being ‘very poor’ — according to data from Central Pollution Control Board (CPCB).
An AQI of up to 50 is considered ‘good’, 51-100 ‘satisfactory’, 101-200 ‘moderate’, 201-300 ‘poor’, 301-400 ‘very poor’, and 401-500 ‘severe’. Above 500 is ‘severe-plus’, or ‘emergency’.
The concentration of harmful pollutants in the city’s ambient air also reduced. While Particulate Matter (PM) 10 was recorded at 411 microgramme per cubic metre (ug/m3) in ‘very poor’ category, PM2.5 was at 260 ug/m3, in ‘severe’ category, according to the website of System of Air Quality and Weather Forecasting and Research (SAFAR) under the Union Ministry of Earth Sciences. The figures were at above 500 and 300 ug/m3 respectively a day earlier.
While the haze that had engulfed the city on November 1 lifted marginally, visibility remained low.
According to forecasts, conditions will improve November 3 but air quality will still remain on the upper side of the ‘very poor’ band.
“Drastic reduction is recorded in effective stubble fire counts (268) over northwest India (Haryana and Punjab) during the last 24 hours after touching a peak value of 3,178 on October 31, said SAFAR.
Accumulation of pollutants sharply increased in the wake of favourable boundary layer meteorology prevailing between Delhi and stubble burning region. This means the direction of winds was towards Delhi.
This was further supported by calm surface wind conditions of the city sharply increased and stubble share in Delhi's PM2.5 touched the season's high of 44 per cent on October 31 and 38 per cent on November 1.
That share has now been said to drop down significantly to 17 per cent, owing to a reduction in fire counts and change in upper wind direction to northerly instead of north-north-westerly.
Western Disturbance (WD) as a cyclonic circulation over Jammu and Kashmir persisted at 3.1 km above mean sea level; another fresh WD was approaching.
“The WD is likely to positively influence Delhi's air quality by increasing surface and boundary layer winds speed and thereby flushing out the accumulated pollutants and isolated rains that may wash out pollutants. By November 4, further improvement to the lower end of the ‘very poor’ category is expected,” SAFAR said.
Its extended outlook warned three weeks ago about the chance of high deterioration in AQI of Delhi during the last week of October to the first week of November for prolonged period mainly. This was ascribed to a delayed withdrawal of the monsoon that would force stagnant conditions beneath to arrest any external intrusion for a longer period which it says is likely to end now.
Wind speed are now forecast to increase to 25 kmph while the India Meteorological Department has predicted light rain or drizzle for Saturday night and Sunday and also on November 7 and 8.
The situation in other centres in the National Capital Region towns did not improve, with the AQI remaining ‘severe’ in Ghaziabad, Greater Noida, Faridabad, Fatehabad, and Noida.
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