Abundant water-soluble calcium coatings on fine Asian dust particles

<p>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.</p>