The air quality in the city reached 'severe' level in the congested residential areas of north Kolkata on Saturday evening, according to the readings of West Bengal Pollution Control Board.

The air quality index (AQI) read 411 PM 2.5 at the air monitoring station of WBPCB at Rabindra Bharati University, one of the two automated air monitoring stations of WBPCB in the city, a WBPCB official said.

The AQI at the second computerised air monitoring station of WBPCB at Victoria Memorial read at 355 AQI - marked as 'very poor' - at 7 pm, the reading said.

The AQI is an indicator of air pollution caused by three pollutants - NO2, PM 10 and PM 2.5. The index indicates air quality as 'good' for values of 0-100, 'moderate' for 101-200 and 'poor' for 201-300.

On December 10, the AQI at WBPCB's air monitoring station at Rabindra Bharati University, was 407 PM 2.5 which is 'severe' in air monitoring terms at certain period (2 pm).

On the same date (December 10), AQI at the WBPCB's second automatic air monitoring station at Victoria Memorial, which is considered a green zone, read at 327 PM 2.5, "very poor", at 2 pm.

Expressing concern what will be the AQI during Christmas and New year, Environmentalist S M Ghosh said, burning waste in open air on a massive scale at a spot in the northern fringes of the city was also leading to alarming rise in pollution levels but the state was taking very little action.

"The state seemed to be sleeping with one eye open," he said.

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