Kolkata: Want clean air? Step out of home between noon & 4pm

KOLKATA: If someone wants to inhale the cleanest possible air, it is better to venture out between 12pm and 4pm. This time period on Wednesday and Thursday recorded the best ambient air quality with PM2.5 count being lowest — almost within the permissible limit. This is the time to have brisk walking, strenuous exercise which necessitates higher inhalation, said a recent study.
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Eight in the evening to 12 midnight, on the other hand, is the time slot people should stay indoors as the ambient air was at its worst.The PM2.5 count ranged between 160 and 240µg/m3 (microgram per cubic meter). The safe limit is 60µg/m3 .

World Bank funded hyper-local mapping of finer particulate matter, PM2.5, gives deep insight into the pattern of the city’s air pollution and how it changes with the progress of the day.
Beliaghata, Ekbalpore and Garia emerged to be the zones with cleaner ambient air. A vast area in north Kolkata — from Dunlop to Shyambazar — proved to be the most polluted zones on Wednesday and Thursday.
Project ‘Cleair’, through its network of over two dozen sensor-based air quality monitoring devices across the city, revealed an amazing dynamism of the city’s air pollution. The PM2.5 pollution is plotted on the city’s map to produce a set of heatmaps whose colour-scheme changes almost on an hourly basis.
In the most polluted time slot from 8pm to 12 midnight on Wednesday, the PM2.5 count was between 210 and 240µg/m3 at Rabindra Bharati University, Shyambazar and Victoria Memorial.
But, with the progress of the day, pollution level changed. From 12 midnight to 4am, pollution dips marginally, the PM2.5 in north Kolkata then ranged from 190 to 230µg/m3. In the rest of the city, PM 2.5 count ranged between 120 and 190µg/m3. From 4am to 8am, Beliaghata, Ekbalpore and Garia are the places to recover faster from the grip of pollution. From 8am to 12pm, the PM2.5 count hovered around 100, but RBU and Shyambazar were still at 160µg/m3. From 12pm to 4pm on Thursday, air quality improved across the city, including the northern part. PM2.5 concentration plunged below 100µg/m3 .
World Bank’s partner in this project Ideation Technology put up a network of low-cost portable sensor devices capturing localized air pollution data. This is used in conjunction with the feed from existing government-owned reference monitors. The Cleair devices were calibrated by co-locating a number of Cleair devices along with WBPCB’s continuous ambient air quality monitoring stations, said Sanjay Chatterjee, director, Ideation Technology.