The air quality of Calcutta worsened on Monday morning after people celebrated Chhath Puja with firecrackers, officials said.

Besides, with the onset of winter, the chill in the air led to foggy conditions, preventing particulate matters from dissipating further, they said.

The city's overall air quality index (AQI) was 128 at 1 pm, they said.

The AQI was 151 at Dhakuria, 170 at Fort William, 107 at Jadavpur, 124 at Rabindra Sarobar and 162 at the Victoria Memorial area.

An AQI between zero and 50 is considered 'good', 51 and 100 'satisfactory', 101 and 200 'moderate', 201 and 300 'poor', 301 and 400 'very poor', 401 and 450 'severe' and above 450 'severe plus'.

From Friday to Sunday, the city's AQI ranged between 85 and 110, officials said.

Environmentalist Somendra Mohan Ghosh said though the situation at Rabindra Sarobar was not alarming as Chhath Puja was banned there, indiscriminate bursting of firecrackers in Ballygunj, Jadavpur, Patuli, Narkeldanga, Babughat and Princep Ghat took the toll on air quality.

"Since Sunday afternoon, firecrackers were used indiscriminately and it reached its peak in the morning hours of Monday. This aggravated the situation, which was reflected in the index," he told PTI.

An official of the Calcutta Municipal Corporation (KMC) said devotees offered puja at 150 ghats along the banks of lakes and ponds in the city, besides the 18 ghats along the Hooghly river.

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