Slow wind, low temp push Delhi air towards emergency zone
On Wednesday, Delhi suffered its second consecutive “severe” day as the overall air quality index (AQI) recorded 456. On Tuesday this was 425.Updated: Nov 14, 2019 04:19 IST
Air quality will continue to deteriorate to nearly “emergency” levels till at least Thursday evening in Delhi, weather scientists have warned.
On Wednesday, Delhi suffered its second consecutive “severe” day as the overall air quality index (AQI) recorded 456. On Tuesday this was 425.
The levels of ultrafine particulate matter with diameter less than 2.5 microns, PM2.5, also remained above 300µg/m³ for over 24 hours, from 12pm on Tuesday. The Indian standard for it is 60µg/m³. The PM10 (coarse dust) level has also been inching closer to the 500µg/m³, while the safe limit is 100µg/m³.
Prolonged to exposure to either particulate matter is known to cause respiratory distress and symptoms of asthma. Ultrafine PM2.5 in particular can penetrate internal organs and cross the blood-brain barrier and cause damage.
Scientists at the India Meteorological Department (IMD) said that the weather had a key role to play in increasing pollution levels in the capital over the last two days. On Wednesday, along with low wind speed, low mixing height (the height above the surface throughout which a pollutant can be dispersed; a higher mixing height allows pollutants to escape into the upper layer of the atmosphere and not get trapped near the ground. ) and the north westerly winds carrying stubble burning residue from Punjab and Haryana also added to the pollution levels in the Capital.
System of Air Quality and Weather Forecasting and Research (Safar), ministry of earth science’s weather and air quality forecasting centre,shows that on Wednesday the share of stubble burning in Delhi’s air was 22%, a marginal dip from Tuesday’s 25%.
“The air quality will continue to deteriorate till Thursday afternoon, but by evening there is a possibility of things getting better. From Friday winds will pick up to nearly 15-20kmph and by the weekend, AQI is likely to settle in the ‘very poor’ category,” said a senior IMD scientist.
Scientists explained that just like Tuesday, on Wednesday too, cloud cover combined with a layer of smoke enveloping Delhi, locked sunlight and did not allow the sun to heat up the surface.
The average wind speed on Wednesday, reduced further to 6-7kmph against 8 kmph the previous day. From early morning till 11.30 am, the winds were calm (zero speed), which is conducive to accumulation of pollutants.
“Winds have largely been calm while sunlight has been diffused. Strong winds are expected to prevail between November 15 and November 18, when air quality will improve remarkably,’ said Kuldeep Srivastava, head, regional weather forecasting centre, IMD.
Srivastava, however, said that the night temperature is expected to rise by a few notches over the next few days while the day temperature will mostly remain stable.
“It is a rise in day temperature, which helps heat up the surface and allows vertical movement of air by making it lighter. The rise in night temperature will not have a significant impact on dispersal of pollutants. It will mainly be the good winds that may help improve air quality,” he added.
On Wednesday, the minimum temperature was 13.4 degrees Celsius while maximum settled at 28.3 degrees C. On Tuesday, the night temperature was 11.7 degrees C, two notches below the season’s average. It was the first time this season that the minimum temperature fell two notches below average.