Southern scandinavian aerosol composition and elemental size distribution characteristics dependence on air-mass history

The influence of aerosol long range transport in southern Sweden was investigated from a data base consisting of simultaneous cascade impactor measurements at three sampling stations, two coastal and one inland rural location. The study focused on S and heavy metals determined by particle induced X-ray emission (PIXE) analysis. The influence of local emissions was minimized by eliminating samples which were strongly suspected to be contaminated. These were identified through size distribution alterations in combination with the concentration levels obtained. Based on air mass back trajectories the samples were classified into either a southern, a northern or an eastern sector or into one of the buffer sectors located in between the sectors mentioned above. Sector S elemental concentrations were generally one order of magnitude higher than those of sector N, while intermediate concentrations were found in the E sector. Intercomparisons of simultaneous fine mode elemental concentration measurements classified into sectors S and N, respectively, provides a method for calculating the sector S foreign contribution of the elemental concentrations in southern Sweden. These calculations, not based on emission data, result in a foreign contribution of the order of 50-90 % (lowest for components like V and Ni and highest for Ti, Mn and Zn) to the metal concentrations. The multivariate statistical method SIMCA revealed that the sector S aerosol elemental composition was dependent on particle size in the accumulation mode. Elements such as S and V (or Ni) normally assumed to originate mainly from the same sources (fossil fuel combustion) were clearly separated and instead S clustered with K, Mn and Zn. This indicates that the transformation processes are more important for the covariation of S with other elements than the source origin. Transformation of SO ₂ in hygroscopic particles rich in K., Mn and Zn (compared with less hygroscopic particles rich in V and Ni) is a possible mechanism which would explain the results found.