All seven air quality monitoring stations in Calcutta reported “poor” air quality on Thursday, while three stations in Howrah reported “very poor” and one “poor” air
quality.

The worst air quality parameter in the National Air Quality Index is “severe”, only one level worse than “very poor”.

Scientists warned that the situation is likely to worsen with the advancing winter. As the temperature drops, the pollutant-laden air close to the ground takes time to rise, hindering the dispersal of the toxic particulates.

In Howrah, the monitoring stations in Dasnagar, Ghusuri and Padmapukur reported “very poor” air at noon on Friday. There was no change in the readings at 6pm.

A scientist at the state pollution control board (PCB) said the air quality reported at any point of time in a station is the average of the air quality of the previous 24 hours.

Belur Math was the only monitoring station in Howrah, out of the five the city has, that reported “poor” air quality. Data at the station in the botanical garden in Shibpur was “insufficient”.

In Calcutta, the air quality was “poor” at all seven stations — Ballygunge, Jadavpur, Fort William, Rabindra Sarobar, Rabindra Bharati (BT Road campus), Victoria Memorial and Bidhannagar.

According to the National Air Quality Index, prepared by the Central Pollution Control Board, “very poor” air can lead to “respiratory illness on prolonged exposure”.

A doctor told The Telegraph that people can experience choking and irritation in the eyes and throat. The air quality index says “poor” air can cause “breathing discomfort to most people on prolonged exposure”.

“Those with chronic obstructive pulmonary disease (COPD) and asthma will have their symptoms aggravated because of worsening air quality,” said one doctor.

A drop in the air quality also weakens the body’s natural defence making people more prone to illnesses.

According to the Alipore Met office, the maximum temperature recorded on Thursday was 28.1 degrees Celsius, which was normal. The minimum temperature was 17.6 degrees, a notch above normal.

The Met office has predicted that the mercury would slide by another three degrees in the next few days.

“Cool air is heavy and cannot rise as fast as the warm air during summer. As a result, cold air hangs closer to the ground and the pollutants are trapped. This exposes us to polluted air. Also, the wind speed drops during winter, slowing the dispersal of the pollutants,” said a scientist at the state pollution control board.

Scientists urged the authorities to crack down on the open burning of waste and force construction sites to take measures so that the dust generated there cannot spread and pollute the surroundings.

If not checked, these two factors can exacerbate the suffering, they warned.