Mineral aerosols and source identification

Abstract

Saharan aerosol and fractionated soil samples have been analysed with X-ray diffraction in order to compare the aerosol mineral composition with its source material. The soil samples used for this study contained only particles with radii r ≤ 5 μm generated by a dry fractionation procedure. This soil size fraction can be expected as most relevant for atmospheric processes such as long-range transport, radiation balance, formation and composition of precipitation. The mineral constituents of both types of samples turned out to be rather similar in composition. Even the aerosol samples from the interior of the desert did not show any significant differences which can be attributed to different or typical source regions. The homogeneity of the aerosol composition is obviously due to the fact that the aerosol over the desert itself is already well mixed as a product of continuous deposition and uptake of material from the ground. The composition of the individual soil samples reflects the major petrography. High contents of calcite and palygorskite in samples of the northern desert are the only significant deviations from the average composition. Therefore, calcite and polygorskite can be considered as tracers for atmospheric mineral dust derived from the northern Sahara. © 1987.