In order to characterize the Siberian aerosol, more than 120 samples for single-particle analysis have been collected simultaneously at two sampling stations in central Siberia in 1 month's time during February and August 1992. For each sample, 400 particles have been analyzed with automated electron probe X-ray microanalysis. Hierarchical cluster analysis allowed us to identify nine major particle types. The differences in aerosol composition were found to be bigger between the winter and summer campaigns than between the two sampling locations. Nonhierarchical cluster analysis combined with 36-h backward air mass trajectories permitted us to compare the abundances for the major particle types for four different source sectors. Results showed significant, though not enormous, differences. Source identification by principal factor analysis allowed the identification of several sources for the Siberian aerosol. Our results provide ample evidence for a long-suspected contribution to Arctic pollution by industrial complexes in the former Soviet Union.