According to the Finnish Meteorological Institute the air of Finnish cities has become cleaner in the past decade. For instance carbon monoxide concentrations in city air have halved in ten years.
A reason for this improvement is for instance the refinement of traffic exhaust fumes thanks to catalytic vehicles. In the future the development will be affected by the growing share of diesel-fuelled vehicles as well as new technology and standards regulating the volumes of emissions.
The reduction of road dust from traffic has not been as successful. Road dust in nearly every part of Finland has remained on the same level as in mid-1990s. Difficult road dust days were on average six per year.
Acidification and the quantity of odor nuisance caused by sulfur compounds have reduced significantly. Many forest and forest industry municipalities are already approaching back-ground levels. For instance the amount of sulfur compounds causing odor nuisance has dropped by 70 per cent since the mid-1990s.
The research of Finnish Meteorological Institute analyzed over 120 long-lasting measurement sequences from 41 measuring stations from all over Finland.