Image: YLE / Lassi Lähteenmäki

People in the city centre of Turku have reported an unfamiliar stench in the air.

The city's air pollution expert Miika Meretoja says that most smells can be explained away by weather conditions.

"Autumn weather is tricky. When the night is calm and cold, a phenomenon known as atmospheric inversion can occur," he says.

The phenomenon can trap pollution close to the ground instead of letting it dissipate. Meretoja says that inversion is strengthened by winds off the still-warm sea.

"Another thing that is likely to cause untoward smells are sewers," Meretoja continues. "There hasn't been much rain lately and sewers are dry."

City dwellers concerned about waste plant

The Yle Turku bureau has received several messages from residents who say the smells are coming from the Topinoja area, where there is a waste management plant and a biogas facility run by the natural gas company Gasum.

Olga Väisäinen, Gasum's communications director told Yle Turku she's not aware of any abnormal odours coming from Tapinoja.

She said because of the reports of odours in the area the last few days, the company would investigate its practices, adding that the company is actively assisting in figuring out the source of the smell.

Meretoja said that people react to smells in very different ways, saying the task of tracking them down is generally quite difficult.

"Attitudes and opinions towards odours are very individual," Meretoja said. "For some, smells can even interfere with peoples' sleep, while others don't even notice them."

Meretoja says that it could take some time and work before the source of the mysterious odour is tracked down.