Kol: Temperature drop pushes up air pollutant levels
Times of India | 24 November 2022
KOLKATA: The drop in temperature to 16.9 °C on Wednesday had an immediate impact on the ambient air quality across the city.
After a brief respite for a couple of days, the city's ambient air once again swung back to its 'poor' (AQI range: 201-300) status. The air quality might degrade even further in the next two days with the wintry chill persisting, pollution control board (PCB) scientists warned. The lowest temperature on Wednesday dropped by almost 2°C.
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"The earth's surface has become cooler than the upper atmosphere. This phenomenon, known as thermal inversion, leaves pollutants hanging close to the ground at a breathable height, putting residents at greater risk. In other seasons, we might emit similar amounts of pollutants, but they escape high in the atmosphere because of the warmer earth's surface," said a PCB scientist.
Indian Council of Medical Research said poor air quality caused breathing discomfort among most people on prolonged exposure. "It is particularly bad for people with pre-existing respiratory issues. We urgently need a graded response action plan (GRAP) to give citizens some relief," said Bonani Kakkar, founder of People United for Better Living in Calcutta (PUBLIC).
The air quality of Ballygunge and Salt Lake, particularly, worsened considerably on Wednesday. In the afternoon, the air quality measured at these two stations hovered above 290. If it crossed the 301-mark, the air quality would have turned 'very poor'. "Under these circumstances, people should refrain from getting exposed to ambient air. The finer particulate matter travels to the lung and causes serious respiratory ailments. We are witnessing a rise in the number of respiratory distress patients at our OPDs," said senior pulmonologist Arup Halder.
The Rabindra Sarobar continuous ambient air quality monitoring station (CAAQMS), which usually shows the best possible air quality in the city, also indicated 'poor' throughout the day. The only CAAQMS that showed 'moderate' air quality is the one at Fort William.
"The north-easterly wind is probably carrying pollutants to the Hooghly from the Maidan area," said a scientist.
"Winter is a special challenge when inversion and cool and calm weather trap and spike daily pollution. This year, even though the average level of PM2.5 in summer and monsoon was considerably lower than that in the previous year due to the pandemic, the winter PM2.5 concentration has risen compared to that of 2019 winter in many cities across regions," said Anumita Roychowdhury, CSE's executive director in charge of research and advocacy.