Kolkata air quality deteriorates with drop in temperature

KOLKATA: With a further drop in temperature, the city's air quality index (AQI) closed the gap between 'poor' (201-300) and 'very poor' (301-400) on Tuesday.
Two air quality monitoring stations - Rabindra Bharati University in the north and Victoria Memorial in the south - consistently showed an AQI above 260, leaving most of the people to suffer breathing discomfort on prolonged exposure.

"Thermal inversion is at play with pollutants hanging at breathable height," said a PCB scientist. Thermal inversion is a reversal of the normal behaviour of temperature in the troposphere (the region of the atmosphere nearest to Earth's surface), in which a layer of cool air at the surface is overlain by a layer of warmer air (Under normal conditions air temperature usually decreases with height).
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Worse, the AQI of the city is PM2.5 driven which means PM2.5 is the most prominent pollutant. Significantly, ultrafine PM2.5 is considered much more lethal compared to the relatively coarser PM10. The PM2.5 particle is about 3% the diameter of a human hair, and can travel straight into the bloodstream. The noxious chemicals ride piggyback on these particles to play havoc with human health.
"There has been tremendous growth in vehicular traffic on AJC Bose Road, increasing the pollutant load around the station at Victoria Memorial. The same is applicable to Rabindra Bharati University's monitoring station. However, two stations - Fort William and Rabindra Sarobar - consistently showed moderate AQI (101-200)," said PCB chairman Kalyan Rudra.
In fact, the city's AQI may worsen further with a Bose Institute study showing a spike of aerosol pollution in the state by 8% and continuing to remain in the "highly vulnerable" red zone for aerosol pollution. The aerosol pollutants will only increase the count of PM2.5 and PM10 in the air.
The vehicular population has a record rise in the city and its suburbs. Apart from the noxious fume of vehicles, factories, open burning, and thermal power stations continued belching smoke in the air. "We need strong mitigating measures by the state pollution control board, Kolkata Police and civic body," said environment crusader Subhas Datta.
Centre for Science and Environment (CSE) said Kolkata needs a deep cut in average PM2.5 levels. "The peak winter pollution shows that the city needs a graded response action plan (GRAP) to relieve citizens by slowing down the peaking of winter pollution," said Anumita Roy Chowdhury, executive director, CSE.