Street dust in Helsinki last Wednesday.The drier weather replacing last Saturday’s snow and sleet has brought with it air quality problems that typically blight Finnish cities every spring.

In Leppävaara in Espoo, the air quality was poor on Monday morning because of high concentration of particles mainly from street dust. At 8 o’clock, pollution levels hit 166 microgrammes of pollution particulates per cubic metre per hour when the limit for poor air quality is 100 microgrammes.

The concentrations of these PM10 particulates exceeded the limit for poor air quality on Hämeenkatu in Tampere (164 microgrammes), Mannerheimintie in Helsinki (154), in Tikkurila in Vantaa (142) and in the centre of Hämeenlinna (137). The cold and windless night gave rise to a temperature inversion, a condition in which the exhaust fumes from the morning rush hour traffic became trapped near the ground, serving to make the air quality even worse.

Measuring stations in the Capital Region recorded values exceeding daily pollution limits on several occasions already last week.

Last Sunday, Helsingin Sanomat reported that Paris is going to impose a partial ban on private motoring in a bid to limit air pollution as the PM10 particulate concentrations reached 180 microgrammes, according to the BBC. In Finland, figures as high as this are extremely rare, says Maria Myllynen, air quality expert from the Helsinki Region Environmental Services Authority (HSY).

“In 2012, the highest daily concentration of particles, 164 microgrammes, was recorded along Ring Road I in Malmi in the spring.”

In Leppävaara, the highest concentration measured around the same time was 135 microgrammes.

The air quality in the capital area may be even worse on Monday afternoon as the sunny weather will dry up road surfaces.

“At least last week, the air quality problems became worse towards the afternoon,” remarks Myllyniemi.

She estimates that period of dusty conditions are a couple of weeks early this year. Cities and the regional Centres for Economic Development, Transport and the Environment have washed grit off some of the roads, which has improved the situation to some extent.

Under the current EU regulations, the concentration of PM10 particulates must not exceed the limit values at the same measuring stations more than 35 times a year.

For example in Leppävaara, the limit has been exceeded three times so far this year.

The weather is set to remain fairly cold and dry for the early part of the week, promising dusty road surfaces and trapped exhaust fumes for cities.

“It remains to be seen whether the warmer weather at the end of the week will melt the snow, making road surfaces wet,” speculates Myllynen.

Samuli Laita – HS
Niina Woolley – HT
Image: Jussi Nukari / Lehtikuva