The air quality in Calcutta worsened on New Year's Day, mainly due to the bursting of firecrackers at midnight, an official of the West Bengal Pollution Control Board (WBPCB) said.

Immediately after the midnight celebrations, the air quality index (PM 2.5) turned 250 in some southern and northern parts of the city, with smog reminiscent of Kali Puja night.

However, it dipped slightly on Monday morning but some places such as Ballygunge and Jadavpur still experienced poor quality air of AQI 281 till 1 pm, the official said.

Air monitoring stations at Victoria Memorial recorded marginally better AQI at 199, followed by 161 at Rabindra Sarobar and 152 at Bidhannagar, he said.

While an AQI of 200 and above is classified as 'poor', the readings between 100 and 199 are categorised as 'moderate', both causing breathing discomfort to people with lung and heart diseases.

Bursting of firecrackers coupled with particulate matters hanging in the air in winter, plus more number of cars hitting the roads in stretches such as EM Bypass, JL Nehru Road, Sarat Bose Road and Sector V compounded the situation for a few hours, he said.

Aided by breezy and sunny weather conditions, the average AQI levels came down to around 170 by 12 pm on Monday, he added.

Environmentalist Somendra Mohan Ghosh said the AQI in the city was still better than last year's levels.

Exactly a year ago, the AQI was recorded at 314 at Bidhannagar, 319 at Rabindra Bharati University, 303 at Victoria Memorial and 269 at Ballygunge.

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