Even 11 days after Diwali and Kali Puja festivals, air quality remained 'very poor' on Friday in several pockets of Calcutta, causing serious health concerns to citizens.

While Ballygunge area in the southern part of the city recorded an air quality index of 309 at 1 pm, the readings of the monitoring station at Victoria Memorial showed AQI at 310 and Fort William at 309, a West Bengal Pollution Control Board (WBPCB) official said.

All these AQI readings were categorised as 'very poor' in environmental terms and indicated how the conditions worsened in 24 hours with the onset of winter, he said.

In the northern part of the city, the air quality was recorded at 286 at Bidhannagar, 218 at Rabindra Bharati University and in the south, the AQI was at 260 at Rabindra Sarobar, he said. The readings were classified as 'poor'.

A day before Ballygunge had recorded AQI of 296, Bidhannagar (284) and Jadavpur (252) and Rabindra Sarobar (254).

Till a week ago, the AQI hovered between 100-200 (moderate) while on Tuesday, the average air quality ranged between 160-220 in the city.

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

During the Kali Puja and Diwali festivals, the AQI ranged between 189 and 255 across the city.

The official said as the wintry conditions set in and the temperature dipped below 20 degrees celsius on Friday morning, cases of respiratory problems have started to spiral.

"An AQI between 201 and 300 causes health alert, over 300 triggers health warnings of emergency conditions," he said.

Environmentalist Somendra Mohan Ghosh said, "The entire population is likely to be affected by serious health effects if there is no rain caused by depression or other weather disturbances in a few days."

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