The air quality in the city deteriorated to 'poor' on Wednesday following the Kali Puja, Diwali and "Bhai Phonta" festivities, according to the readings of West Bengal Pollution Control Board (WBPCB).
The Air Quality Index (AQI) read 233 (PM 2.5) at air monitoring station of WBPCB at Rabindra Bharati University in north Kolkata at 8 am, an official of the board said.
AQI between 201 to 300 mark is categorised as 'poor' and 'very unhealthy' and can cause respiratory problems.
The PM 2.5 (particles in the air with a diameter of less than 2.5 micrometres) level at the air monitoring station at Jadavpur in south Kolkata read 218 around the same time, the official said.
The corresponding PM 2.5 level at Ballygunge stood at 207 while that of Fort William in the green zone in central Kolkata touched 201, he said.
"AQI in three monitoring stations deteriorated to 'poor' on Tuesday morning from 'moderate' (PM 2.5 level 101- 200) since the beginning of Kali Puja festivities. However, this can be attributed to the rise in moisture levels in the air," he said.
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AQI read 184 PM 2.5 at the air monitoring station at Victoria Memorial, while that of Rabindra Sarobar read 191 and of Bidhannagar read 187, the official said.
"Although the readings in these three monitoring stations were categorised as 'moderate', they were all closer to the 200-mark indicating at rising pollution level in those areas as well," environmentalist Somendranath Ghosh said.
The PM 2.5 level at Ghusuri, an industrial pocket in the twin city of Howrah, turned an alarming 302 which is highest in the metropolitan area in the past few days, an official said.
Ghosh said the rise in AQI can be attributed to unrestricted use of firecrackers during immersion and Diwali celebrations apart from vehicular emissions and burning of chullah (wood-fired stove).