Delhi’s air worst since Nov 10, no relief likely before Monday

New Delhi: Friday was Delhi’s worst air day in over two months, with the air quality index (AQI) touching 460 in the “severe” category due to a mixture of low wind speed, high relative humidity and a low boundary layer trapping pollutants closer to the surface. A visible haze blanket remained throughout the day and visibility was low.

The last time Delhi had a higher AQI was on November 10 when it was 476, but stubble burning was then a factor. The current scenario is all down to meteorological factors, with conditions not expected to improve much in the next 48 hours, said experts. At 429, AQI deteriorated to “severe” on Thursday.

Kuldeep Srivastava, scientist at India Meteorological Department and head of Regional Weather Forecasting Centre in Delhi, said the city was experiencing “calm winds”, with speed only touching 5km/hour during the day. “Only from Monday will wind speed pick up, with easterly winds influencing the region. Some dispersal may take place then,” said Srivastava.

“There is moisture in the atmosphere and pollutants are gradually accumulating in the air. The air quality has, therefore, worsened over the last 24 hours. The boundary layer is also low due to low temperatures. All these factors are combining to cause such a situation,” he added.
According to System of Air Quality and Weather Forecasting and Research (SAFAR), this is likely to be the first prolonged “extreme air pollution event” of 2021 and secondary particulate formation may also occur. “The minimum temperature is likely to fall further. AQI is forecast to deteriorate further and rapidly,” SAFAR stated.

“The secondary particulate formation, which multiplies the finer particles under congenital conditions, have already started as predicted and will accelerate under present conditions,” it added. Extremely low ventilation and shallow boundary layer height are adding to the severity.

On Friday, AQI in Noida, Greater Noida and Ghaziabad was in the ‘severe’ category. While Ghaziabad’s AQI was at 461, in Greater Noida, it was at 458 and in Noida, the AQI was 469. According to CPCB’s central control room, Delhi-NCR’s 24-hour average PM2.5 concentration was over five times the standard at 335 micrograms per cubic metre at 8pm. The average PM10 concentration was 483 micrograms per cubic metre. The standards for PM2.5 and PM10 are 60 and 100 micrograms per cubic metre, respectively.