Air quality in Kolkata worsens as AQI slips into ‘Poor’ category ahead Diwali

For the first time this season, Kolkata’s air quality saw a significant decline, with one of the city’s monitoring stations recording an Air Quality Index (AQI) in the ‘poor’ category. Ballygunge and Salt Lake were the worst-hit areas, where the AQI exceeded 201, marking a noticeable shift from the previously ‘good’ and ‘satisfactory’ levels recorded throughout the summer and monsoon months.

The deterioration in air quality is being attributed to a combination of factors, including prevailing cloud cover and a reduction in vertical wind flow, which trapped pollutants closer to the ground. A scientist from the Pollution Control Board (PCB) explained that the conditions allowed pollutants to linger in the lower atmosphere, causing the air to become unhealthy to breathe.

However, relief came in the form of an evening downpour, which temporarily cleared the air. The PCB expects the next day’s AQI readings to reflect this improvement, though concerns remain over a more prolonged dip in air quality as the winter season approaches.

Kolkata’s eight continuous ambient air quality monitoring stations (CAAQMSs) recorded varying levels of pollution, with Ballygunge and Salt Lake crossing the 200 mark, while the other stations remained in the ‘moderate’ range. The trend is likely to continue in the coming weeks as the city experiences its pre-winter spike in pollution.

This annual spike in pollution mirrors trends observed across the Indo-Gangetic Plain (IGP), where pollutants accumulate in the valley and drift toward Bengal. Winter conditions, marked by an inversion of the planetary boundary layer, are expected to exacerbate this situation, as cooler air traps pollutants closer to the ground.

A "capping inversion" further complicates the issue. This phenomenon occurs when a layer of cooler air overlays a warmer one near the earth’s surface, preventing the warm air and the pollutants within it from rising. As a result, pollution builds up near ground level, significantly degrading air quality.

Experts warn that if immediate measures are not taken to control emissions, Kolkata's AQI could further deteriorate, posing serious health risks to residents, particularly during the post-Diwali period and through the winter months.