Source contributions to PM2.5 particles in the urban air of a town situated close to a steel works

The most significant fine particle sources and their fractions in the subarctic city of Raahe, Finland, were determined by using receptor modelling. The daily mean concentrations of PM2.5 and PM10 particles, sulphur dioxide and reflectance of PM2.5 filters were monitored for four months between January and April 1998 at a site about 3.5 km from the local steel works, the main stationary particle source in the city, and about 1 km from the city centre. PM2.5 particles were analysed for a total of 31 elements by inductively coupled plasma mass spectrometer in order to identify the sources. Concentrations of three anions (F−, Cl−, SO42−) were also analysed by ion chromatography. The receptor model was based on a factor analysis-multiple regression. The method enabled five main PM2.5 emission sources to be identified: long-range transportation (44%), the sintering plant of the steel works (11%), the steel smelting plant of the steel works (3%), soil and street dust (7%) and a mechanical engineering works, which had a negative effect on the particle load. Unidentified sources were responsible for 35% of the PM2.5 particles on average. The contribution of the mechanical engineering works could not be determined because the used marker gave a negative effect due to the wind direction. The works had the sea (Gulf of Bothnia) beyond it, so that when the wind was blowing from that direction towards the monitoring site, it brought in clean air masses to dilute emissions from the mechanical engineering works efficiently.