Ca-containing particles, especially CaSO 4 particles, have been encountered in several atmospheric aerosol studies. An overview is given of the different sources of airborne Ca-containing particles. The North Sea atmosphere is studied to identify the different Ca-containing particle types and to find the correlation between their occurrence and the source regions of the corresponding air masses. About 50 000 individual aerosol samples were collected above the Southern Bight of the North Sea for several wind directions and analyzed for their composition using electron probe X-ray microanalysis. Nonhierarchical cluster analysis is performed on the data to reveal the different particle types, their relative abundances and their sources. CaSO 4 in most cases constitutes the largest fraction of the Ca-containing particles. Extremely high numbers of CaSO 4 particles are found for northeastern winds, coming from the central part of Germany, suggesting that a great fraction is derived from anthropogenic sources located in this region. Among the other Ca-containing particle types are the aluminosilicates, CaCO 3 , Fe-Ca-rich particles, and CaSO 4 or CaCO 3 in combination with NaCl.

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Aerosol samples have been collected over the southern bight of the North Sea from an aircraft. In this way, 96 samples were taken for single-particle analysis during 16 flights. Almost 45 000 individual particles were analyzed with electron probe X-ray microanalysis. More than 5000 of these were found to contain significant concentrations of one or more of the heavy metals Cr, Pb, and Zn. With the help of hierarchical, nonhierarchical, and fuzzy clustering techniques, various heavy metal-containing particle types could be identified. Significant differences in abundances were detected in the North Sea heavy metal aerosol, depending on the origin of the air masses. In samples with continental influence 50 times more Zn-and Pb-containing particles were found than in samples with a marine history. For Cr, on the other hand, we found abundances in the marine sector that were one-third of the values for continental sectors. This might point to a rather undefined marine source, which could be the recycling of previously deposited material by reinjection into the atmosphere by sea spray. The highest values for Cr-, Pb-, and Zn-containing particles were always detected under southeastern wind directions.

Individual particle analysis using micro‐PIXE and proton backscattering was performed for selected aerosol samples collected over Siberia. Point analyses were complemented by x‐ray mapping for complex particles. Hierarchical cluster analysis of 124 particles identified in general the same particle groups, as found by automated electron microprobe analyses of approximately 25 000 particles from the same locations. However, owing to the superior sensitivity of micro‐PIXE, a number of heavy metals were identified, suggesting an anthropogenic origin of particles. These metals remained undetected by EPXMA owing to its inferior sensitivity. Elemental mapping of single aerosol particles yielded important information on the chemical heterogeneities. Copyright © 2001 John Wiley & Sons, Ltd.

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