The air quality in the Maidan area sunk to “very poor” on Sunday morning and remained so for much of the daytime forcing morning walkers and hundreds of others enjoying the winter afternoon on the greens to breathe in foul air.

The rest of Calcutta was not much better either. The air quality in Ballygunge, Jadavpur, Rabindra Sarobar and Fort William was “poor” from the morning till late on Sunday.

The air quality monitoring station at the Victoria Memorial recorded “very poor” air at 8am as well as at 2pm, which means both morning walkers and families spending time on the Maidan and adjacent areas in the afternoon were breathing in toxins.

The air quality improved only a little and became “poor” at 3pm and remained so till late in the evening.

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

The index mentions that “poor” air can result in “breathing discomfort to most people on prolonged exposure”.

“The reading at the monitoring station at the Victoria Memorial reflects the air quality on the Maidan and the surrounding areas,” said a senior scientist at the state pollution control board (PCB).

“One reason why the air quality drops at the Victoria Memorial is that various sporting activities on the Maidan raise dust in the air.”

The scientist explained that cooler temperatures and slower wind speed during winter increase air pollution.

“The cooler air does not rise as much as warmer air during summer. The lack of wind speed means the pollutants do not disperse. As a result, the pollutants released from vehicles, industrial units and construction sites remain trapped in the air we breathe,” he said.

At 8am, the air quality monotoring stations at Bidhannagar and Rabindra Bharati University (BT Road campus) did not report air quality citing “insufficient data”.

At 2pm, the air quality was “moderate” at Rabindra Bharati. It remained so till late in the evening. The air quality at Bidhannagar was “poor” at 2pm and remained so till late in the evening.

Like everywhere else in Calcutta, people go on picnic and other outings during winter, but the foul air strikes a jarring note amidst the celebrations.

Doctors cited the rise in air pollution during winter to the spread of respiratory diseases across the city.

“The winter surge of respiratory diseases is still continuing and the air pollution is one of the factors contributing to this. The air pollution breaks the defence mechanism of the lungs and make a person more vulnerable to infection,” said Arup Halder, a pulmonologist at the Calcutta Medical Research Institute (CMRI).