City air quality 'improves a notch' with the rise in temperature, yet to be good
Telegraph | 15 March 2025
The city’s air quality has marginally improved with a rise in the temperatures, but there was yet to be a single day when the air quality was “good”.
An analysis of the air quality report of the 14 days of March till Friday showed that the average air quality of the city was “moderate” on ten days and “satisfactory” on the remaining four days.
In January, usually the coldest month in Calcutta, there were six days when the air quality was “poor” and 25 days when the air quality was “moderate”.
The National Air Quality Index, prepared by the Central Pollution Control Board, says that “moderate” air quality can lead to “breathing discomfort to the people with lungs, asthma and heart diseases”; “satisfactory” air quality can cause “minor breathing discomfort to sensitive people” while “poor” air quality causes “breathing discomfort to most people on prolonged exposure”.
“Good” air quality has “minimal impact” on one’s health.
On Friday, one of the four days this month when the air quality was “satisfactory”, all the stations in Calcutta and Bidhannagar, barring one that had “satisfactory” air quality at 4pm.
The air quality recorded in Jadavpur was “moderate” at 4pm. There are seven continuous air quality monitoring stations in Calcutta and Bidhannagar.
The air quality recorded at any point is an average of the air quality of the previous 24 hours at that station.
A scientist with the state pollution control board said that trends of previous years show that the air quality in Calcutta remains “moderate” on the majority of days in summer. A spell of rain improves the air quality to “good” or “satisfactory” for two to three days at a stretch, but it again drops to “moderate”
“Only in monsoon long stretches of ‘good’ and ‘satisfactory’ air quality days can be found. The rain washes away the pollutants and improves the air quality. But in summer, the dust and pollutants remain suspended in the air as it is usually dry and devoid of rain,” said the scientist.
The air quality worsens during winter because of meteorological factors. “The lower temperatures mean air does not rise as much as in summer. The pollutants emitted get trapped in the air closer to the ground or in the air we breathe. As a result, the air quality drops to 'poor' or sometimes even worse,” he said.
The lower wind speed in winter compared to summer also does not allow pollutants to disperse.
Higher temperatures and greater wind speeds disperse the pollutants in summer.
“Yet it remains moderate on most days because the load of pollutants released by vehicles and the construction industry, among others, is very high,” explained the scientist.