Air quality in certain areas of the metropolis and neighbouring Howrah city turned poor since Wednesday for the first time in past seven months.
A West Bengal Pollution Control Board official attributed the air quality turning poor to change in weather conditions.
While the Air Quality Index (AQI) at the automated air monitoring station at Rabindra Bharati University in north Kolkata was 257 (PM 2.5) at 11 am Thursday, it was 268 (PM 2.5) at around the same time the previous day, breaching the 200 mark (poor) for consecutive two days, the official said.
He, however, said with the retreat of monsoon and onset of winter the fine particulates hang on the air and the AQI shot up as a result. AQI between 201-300 is considered poor in environmental terms and this was the first time since lockdown, that air quality reached that level, the official said.
At Ghusuri in Howrah, which also records spurt in air quality index during the season of October-March due to congested neighbourhood and existence of many foundries, the AQI showed 241 (PM 2.5) on Thursday, the official said.
In other pockets of Kolkata AQI hovered between 100- 150, termed as moderate by environmentalists, for the past two days.
It was 143 at Ballygunje, 136 at Bidhannagar, 150 at Fort William, 157 at Jadavpur and 138 at Rabindra Sarobar on Thursday noon, the official said.
On Wednesday noon AQI read at 169 at Jadavpur, 201 at Fort William, 161 in Rabindra Sarobar, 144 at Bidhan Nagar.
In all these places AQI had not gone over 100 mark in past seven months mostly remaining within 50-70 limits.
Pollution control board chairman Kalyan Rudra said in a press meet last week that November 1 onwards, WBPCB will take measures like spraying water from sprinklers on construction sites to prevent pollutants mixing in air and keep watch on burning of solid waste and crop which aggravate the environmental conditions.