Minor effect of physical size sorting on iron solubility of transported mineral dust

Observations show that the fractional solubility of Fe (FS-Fe, ratio of dissolved to total Fe) in dust aerosol increases dramatically from ~0.1% in regions of high dust mass concentration to 80% in remote regions where concentrations are low. Here, we combined laboratory geochemical measurements with global aerosol model simulations to test the hypothesis that the increase in FS-Fe is due to physical size sorting during transport. We determined the FS-Fe and fractional solubility of Al (FS-Al) in size-fractionated dust generated from two representative soil samples collected from known Saharan dust source regions using a customized dust re-suspension and collection system. The results show that the FS-Fe is size-dependent and ranges from 0.1-0.3 % in the coarse size fractions (>1 µm) to ~0.2-0.8 % in the fine size fractions (