Kolkata breathes easy as high wind speed, temp rise bring AQI to 'satisfactory' level

KOLKATA: Good air quality days have arrived early this year. Though the city got no rain this winter, the air quality across the city has improved significantly to the 'satisfactory' level (AQI: 51-100) and has remained so for four days, thanks to high wind speed and good radiative heat of the earth's surface.
'Satisfactory' defines the second-best air quality on the index.

The air quality in the city started improving from February 19 from 'moderate' (AQI: 101-200) to 'satisfactory'. Usually in February, there are one or two 'satisfactory' days but rarely does it stay longer. "Citizens have suffered all kinds of breathing distress and respiratory ailments. They can now breathe easy," said senior pulmonologist Arup Halder.
The rising temperature, too, helped clean the air. The city's maximum temperature on Thursday was 32.5 degrees Celsius, two notches above normal, and minimum 22.8 degrees, four notches above normal. "The improvement in air quality is largely due to the atmospheric condition, called ventilation coefficient, which is the product of mixing depth and the average wind speed. It gives an indication of the air quality and pollution potential or the ability of the atmosphere to dilute and disperse the pollutants over a region," said state pollution control board chairman Kalyan Rudra.
Some stations, like Salt Lake, Jadavpur and RBU, which recorded the worst AQI this winter, showed dramatic improvement. On Thursday, the AQI at Salt Lake and Jadavpur plunged below 77, except for RBU and Victoria, where it was 95 and 86. "If the atmospheric condition prevails like this, the AQI may improve to even 'good' (0-50)," said a PCB scientist.