Silicon and aluminum in atmospheric aerosols: Crust-air fractionation?

Abstract Existing data show that Si Al in the atmospheric aerosol is 35–50% lower than in the average crust, with nonurban Si/Al 20% lower than urban Si/Al. The high correlation between Si and Al concentrations in the aerosol strongly suggests that crustal material is their only source, and leads to the inference of major crust-air fractionation for Si and A1. The basic fractionation mechanism is proposed to be a large contribution of aggregated clay minerals (having low Si Al ) to the total Si and Al of aerosols. For urban areas fly ash and anthropogenic dusts may also affect Si Al . Accurate calculation of the crustal contribution to the aerosol must therefore be referred to crustal aerosol, whose composition is not yet known, rather than to the traditional average crust.

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