Updated: October 18, 2020 9:52:32 am
Delhi’s air quality deteriorated within the ‘poor’ category on Saturday as the share of pollutants from stubble burning increased to an estimated 19%. The average air quality index (AQI) of the capital on Saturday was 287 in the ‘poor’ range, higher than 239 recorded on Friday, as per the Central Pollution Control Board (CPCB).
Air quality of neighbouring NCR towns also worsened within the ‘poor’ category. AQI of Gurgaon and Ghaziabad was 280 and 289, while Noida and Greater Noida’s AQI deteriorated to ‘very poor’ range with a reading of 309 and 330.
A forecast from the Central government’s System of Air Quality and Weather Forecasting and Research (SAFAR) said, “Delhi’s AQI likely to stay in higher-end of ‘poor’ to the lower end of ‘very poor’ for tomorrow, and likely to improve to the ‘poor’ category by October 19. Further improvement is expected by October 20.”
The forecast added that there has been an increase in fire counts in Punjab, Haryana and neighbouring border areas, where crop residue burning is presently underway. On Friday, as per SAFAR, there were around 882 fire counts.
Wind direction over Delhi is from the north-west, which is favourable for transporting pollutants from stubble burning in Punjab and Haryana and, therefore, contribution of farm fires to PM 2.5 in Delhi was estimated around 19% on Saturday, as per SAFAR.
Calm wind conditions, in which wind speed drops to zero, will continue during night time and early morning hours in Delhi for at least the next three days, and during the day time, the speed would pick up to 8-10 kmph, as per the India Meteorological Department (IMD).
Kuldeep Srivastava, head of IMD’s regional weather forecasting centre in Delhi, said higher wind speed in day time would help in slow dispersion of pollutants. Wind direction over the city is also expected to be from the north-west for the next three days.
Minimum or night-time temperature in the city has also been steadily dipping. At the IMD’s Safdarjung observatory, which is representative of the city, the minimum temperature recorded on Saturday was 16.8 degrees Celsius, three degrees below normal. On Friday the minimum temperature was 16.4 degrees.
Low temperatures and wind speed reduces the mixing depth or the vertical height in which pollutants are suspended, leaving them trapped closer to ground. Srivastava also said the city would see misty mornings in the coming days.
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