At 6 pm, the AQI reading was 321 at Fort William, 319 at Ballygunge, 317 at Jadavpur and 308 at Victoria Memorial. The AQI reading was in the ‘poor’ category at Rabindra Sarobar and Bidhannagar with PM2.5 staying at 285 and 233, respectively. Only the AQI at Rabindra Bharati University, was 179 which is in moderate category.

The air quality in neighbouring Howrah district also remained poor with an AQI reading of 278 at Belur Math.

WBPCB chairman Kalyan Rudra said that it was not uncommon for the air quality to turn poor due to weather conditions.

“The sky over the indo-Gangetic plain has been overcast and the wind speed was low. Due to these factors and low ventilation coefficient, the air quality deteriorated. This means that the air pollutants could not disperse,” said Rudra.