Calm winds push Delhi’s AQI back up to 374; ‘very poor’ stretch to continue

DSS shows stubble contribution down to 5.43%; IMD notes wind speeds below 10 km/hr and colder nights sustaining pollution despite easing farm-fire transport.

Delhi’s air quality remained in the ‘very poor’ category for the fifth straight day on Tuesday, slipping again as wind speeds dipped across the region. The 24-hour average air quality index (AQI) stood at 374 at 4pm, up from 351 on Monday, according to the Central Pollution Control Board (CPCB). Sunday’s reading was 377, keeping pollution levels oscillating with changing meteorological conditions.

DSS shows stubble contribution down to 5.43%; IMD notes wind speeds below 10 km/hr and colder nights sustaining pollution despite easing farm-fire transport. (Sunil Ghosh/HT)

Monday’s brief improvement was driven by winds picking up to around 12 km/hr during the day. But speeds fell below 5 km/hr on Tuesday, allowing pollutants to accumulate. Forecasts suggest that while the contribution of stubble burning is likely to reduce as winds predominantly turn north-easterly, continued low wind speeds will keep pollution trapped over the city.

“Delhi’s air quality is likely to be in the ‘very poor’ category from November 19 to 21. The outlook for the subsequent six days also shows the air quality remaining in ‘very poor’,” the Centre’s Air Quality Early Warning System (EWS) said.

At Safdarjung, Delhi’s base weather station, the minimum temperature rose slightly to 9.6°C on Tuesday — still three degrees below normal. Monday’s 8.7°C was the lowest since November 30, 2022, when it touched 8.3°C. The minimum is expected to fluctuate between 9°C and 11°C until Thursday, with a persistent winter chill, according to the India Meteorological Department (IMD). A return of easterly to north-easterly winds is likely to push the minimum above 11°C on November 21.

“Wind speed is dipping in Delhi again. It is becoming calm at night and, although it may pick up marginally during the day, it is likely to remain below 10 km/hr,” an IMD official said.

Delhi’s maximum temperature settled at 26.4°C — a degree below normal — and is forecast to hover between 25°C and 28°C until Friday.

Data from the Centre’s Decision Support System (DSS) showed that stubble burning accounted for 16.13% of Delhi’s PM2.5 on Monday, dropping to 5.43% on Tuesday. The highest single-day contribution so far this season has been 22.4% on November 12 — not only lower than previous years but also much later in the season.

Last year, the peak single-day share was 35.1% on November 1. It was 35% on November 3 in both 2022 and 2023, and 48% on November 6 in 2021.