Kolkata: Rain came as a saviour for Kolkata on Wednesday, washing away much of the pollution that had choked the city’s air following three days of incessant bursting of firecrackers. By evening, five of the seven Continuous Ambient Air Quality Monitoring Stations (CAAQMS) in the station turned pale green, indicating ‘satisfactory’ air quality, a welcome respite ahead of the approaching winter.The India Meteorological Department (IMD) stated that a low-pressure area was likely to form over the Southeast Bay of Bengal around Friday following a developing cyclonic circulation near the Andaman Sea. But, an IMD scientist said, so far, it did not look like it would have any impact on Bengal. The overnight showers improved Kolkata’s air quality dramatically with pollution levels dropping between 1 am and 4 am on Wednesday. Although cloudy skies and sluggish winds led to a mild rebound in particulate concentrations on Wednesday morning and afternoon, intermittent showers later in the day helped cleanse the air again.At Ballygunge, the air quality index (AQI) declined from 103 at 1 am to 82 at 4 am and remained largely stable throughout the day, settling at 82 by 7 pm. Salt Lake recorded an even sharper improvement, with its AQI falling from 96 to 73 before reaching 68 in the evening.Fort William witnessed a similar decline, from 91 at 1 am to 68 at 4 am, before settling at 71 by 7 pm. Jadavpur’s AQI dropped from 85 to 66 before ending the day at 71, while Rabindra Sarobar improved from 93 to 68 and registered 75 in the evening.But two monitoring stations remained in the ‘moderate’ category. Rabindra Bharati University on BT Road recorded the highest pollution levels, with AQI rising from 120 at 4 am to 150 at 9 am before declining marginally to 140 by 7 pm. Victoria Memorial registered 108 in the evening, against 118 at 1 am.The fluctuations highlighted the crucial role of weather in determining Kolkata’s pollution levels. While rainfall helped remove suspended particulate matter from the atmosphere, cloud and weak winds could restrict pollutant dispersion, allowing concentrations to build up again, said a PCB scientist.After the rain at night, Kolkata experienced a generally cloudy day with spells of light rain on Wednesday. The maximum temperature hovered around 30°C, while the minimum was around 22°C-23°C. Thursday is expected to bring a change in weather, with morning mist giving way to partly cloudy or mostly sunny skies. Chances of rainfall are considerably lower, though isolated showers could not be ruled out, said the Met office.For environmentalists, such as Subhas Datta and Somendra Mohan Ghosh, the improvement offered cautious relief. With the wintry chill yet to set in, the showers have temporarily delayed the return of stagnant atmospheric conditions that could trap pollutants close to the ground. But as the weather turned drier and temperature began to fall, sustaining Wednesday’s improvement could prove increasingly challenging, said a PCB official.
