Abundant water-soluble calcium coatings on fine Asian dust particles

Abstract

The dissolution behavior of atmospheric calcium (Ca) mineral dust released from arid regions and their climate impacts via buffering effects are highly dependent on their size-resolved mineralogical composition. Due to the inherent complexity of mineral dust, tracing the chemical forms and mixing states of Ca minerals at single-particle level remains challenging. In this study, an automated microanalysis technique was employed to characterize the physicochemical properties of 43 990 individual mineral dust particles generated by saltation-sandblasting processes in two deserts, along with their residual 42 306 particles after water dialysis. Both the total dust and the Ca-containing particles exhibited a modal peak in the submicron size range, before and after dialysis. After dialysis, 56.9 % to 88.2 % (by number) of the calcium-containing dust particles lost their soluble calcium components. These water-soluble elemental Ca accounted for 19.6 %–41.9 % of the mass of elemental Ca in both the Taklimakan and Gobi deserts. In addition, more than 73.2 % of Ca-O-rich and Ca-S-containing particles occurred as water-soluble surface coatings on other minerals and were effectively removed by dialysis. The results provide a realistic constraint for assessing the abundance of water-soluble Ca coatings on fine particles emitted from two Asian deserts.