Air quality in city dips as winter sets in; BMC alert

The air quality in Mumbai has dipped to 'moderate' and the Bandra Kurla Complex has recorded a 'poor' level, prompting the Brihanmumbai Municipal Corporation to instruct officials to implement air pollution guidelines. Experts attribute the drop in air quality to the onset of winter and suggest that the implementation of pollution norms may have been lax.

After remaining ‘good’ in the last few days, the city’s air quality dipped to ‘moderate’ on Tuesday and Bandra Kurla Complex recorded a ‘poor’ level, which prompted the Brihanmumbai Municipal Corporation (BMC) to instruct the 24 assistant commissioners to stay alert in implementation of the civic body’s air pollution guidelines.

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Minesh Pimpale, deputy municipal commissioner (environment), said there is smog with winter setting in. “I have instructed all 24 ward officers to first take care of the nearby areas and they will also have to look at the 27 locations where air monitoring stations are situated, because we have observed that these areas first report a rise in air quality index (AQI).”

While experts attribute the drop in air quality to the onset of winter, they also feel BMC could have probably gone lax in implementing their air pollution norms.

Professor Gufran Beig, chair professor at NIAS, IISC, and founder project director, SAFAR, said, “These guidelines were issued one month ago and AQI showed some improvements then. But with winter setting in, the air quality is likely to drop and even worsen because of two to three factors.”

Since the weather is cool, Beig explained, the atmospheric boundary layer or lid comes down, and the pollutants trapped within the city limits will face an upward dispersion.

Further, when winter becomes severe it tends to reduce windspeed and bring down the inversion layer which is defined as the upper lid of the atmospheric surface, he said. “When pollutants try to go up, this upper lid tries to stop them. When the inversion layer is up at 1km-2km, these pollutants get enough space to go up and disperse and dilute themselves. But if the inversion layer is half a km down then pollutants get less space to go up and disperse and the upper lid doesn’t allow pollutants to mix above that layer.”

Beig said in the month of October, when the winter had not set in, the air quality had worsened. “In spite of having natural advantages, the air quality was going down because of construction and redevelopment activities. BMC’s guidelines did help curb and improve the air quality. Currently, the implementation might not be stringent on the ground with little less policing coupled with the onset of winter leading to AQI levels rising again.”