Little breathing space: Third day of ‘severe’ air in Delhi

While agencies forecast some temporary respite over the next two days with an increase in wind speed that could help disperse pollutants in the region, wind speed will dip again from December 1, keeping the air quality largely between “very poor” and “severe” categories.

Delhi’s air remained in the “severe” category for a third consecutive day on Sunday, clocking an Air Quality Index (AQI) reading of 402 according to Central Pollution Control Board’s daily 4pm bulletin as wind speeds remain low in the region.

Traffic seen at amid low visibility due to dense smog, at ITO on Sunday. (Sanchit Khanna/HT)

While agencies forecast some temporary respite over the next two days with an increase in wind speed that could help disperse pollutants in the region, wind speed will dip again from December 1, keeping the air quality largely between “very poor” and “severe” categories.

An AQI reading between 0 and 50 is considered “good”, 51 and 100 “satisfactory”, 101 and 200 “moderate”, 201 and 300 “poor”, 301 and 400 “very poor”, and 401 and 500 “severe”.

Delhi recorded an AQI reading of 402 (severe) on Saturday, and 406 (severe) on Friday. On Thursday, Delhi’s AQI had touched 400, on the brink of the “severe” category.

Gufran Beig, founder and project director at the System of Air Quality and Weather Forecasting And Research (Safar), said wind speeds had become “calm” over the last 72 hours, but are expected to pick up from Monday. “We were forecasting relief from November 29 onwards and wind speeds will remain good during the day both on November 29 and 30. However, conditions will once again become adverse from December 1, as wind speed and temperatures decrease, dropping the ventilation index too,” said Beig.

According to Safar, only around 200 farm fires were recorded in the northern plains on Sunday, with the share of their contribution to Delhi’s PM2.5 pegged at just 3%. PM 2.5 is fine, inhalable particulate matter with diameters of 2.5 microns. It is about 30 times smaller than a strand of human hair.

According to the Early Warning System (EWS) for Delhi, a forecasting mechanism under the ministry of earth sciences, Delhi’s ventilation index is also expected to improve considerably in the next two days, allowing faster dispersal of pollutants. While it was 2,500 m2/s on Sunday, it could increase to 7,500 m2/s on Monday and 6,000 m2/s on Tuesday.

“A ventilation index lower than 6,000 m2/s with average wind speeds less than 10km/hr is unfavourable for dispersion of pollutants,” said EWS in its daily bulletin on Sunday.

Delhi recorded a minimum temperature of 10.8 degrees Celsius on Sunday, with mercury expected to remain around 10 degrees Celsius on Monday as well. While it could drop below the 10-degree mark on Tuesday, the influence from a western disturbance may take the minimum up to 12 degrees Celsius by Wednesday, the India Meteorological Department (IMD) forecast said.

Delhi recorded a maximum temperature of 26.8 degrees Celsius on Sunday, one degree above normal. Its maximum temperature is expected to hover between 26-27 degrees Celsius for the next three days, the IMD said.

“Shallow fog with a visibility range of 500 to 1000 metres was reported in the early hours on Sunday. Shallow fog will continue across Delhi in the next few days,” said a Met official.