Particulate matter of size 2.5 or PM2.5 are ultrafine particles of diameter less than 2.5 micrometres, which is about 3% the diameter of a human hair, and can travel straight into the blood stream. The noxious chemicals riding piggyback on these particles play havoc with human lives.
People’s response to the ‘janata curfew’ put vehicles completely off the road. There was hardly any bus or taxi on the streets. The automobile emission was almost nil, aiding the environment to heal itself tremendously. “The lockdown reveals how much of the degradation of air quality is anthropogenic or induced by human activities,” said West Bengal Pollution Control Board (WBPCB) chairman Kalyan Rudra.
The PM 2.5 count on Saturday was 53.1µg/m3 (microgram per cubic meter) at Fort William, 57.1 µg/m3 at Rabindra Bharati University (RBU) and 36.8 µg/m3 at Jadavpur. On Sunday, the count plunged below 26.1 µg/m3 at Fort William, 18.2 µg/m3 at RBU, and 14.3 µg/m3 at Jadavpur. While the national daily standard is 60 µg/m3 , the WHO standard is 25.
“The latest source-apportionment study by National Environment Engineering and Research Institute (NEERI) found that road dust constitutes 66% of PM2.5 pollution of city’s ambient air. Apart from the tail-pipe emission, the vehicular movement causes re-suspension of road dust. On Sunday, there was no re-suspension of dust,” said Rudra.
WBPCB has started sprinkling water mixed with dust suppressant chemicals along all major corridors in Kolkata. With the experiment proving a success, WBPCB has extended the exercise till the end of next month. Significantly, from the month of March, air quality improves dramatically for meteorological reasons. Increase of heat and humidity helped finer particulate matters to coalesce into bigger particulate matter.
“The biggest takeaway from the crisis is environmental improvement. I have seen how the air quality index across the city turned green from yellow,” said green crusader Subhas Datta.
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