Department of Chemistry, Aarhus University, DK-8000 Aarhus C, Denmark.
Environ Sci Process Impacts. 2020 Aug 1;22(8):1759-1767. doi: 10.1039/d0em00179a. Epub 2020 Jul 22.
Magnesium and calcium chloride salts contribute to the global atmospheric aerosol burden via emission of sea spray and mineral dust. Their influence on aerosol hygroscopicity and cloud forming potential is important but uncertain with ambiguities between results reported in the literature. To address this, we have conducted measurements of the hygroscopic growth and critical supersaturation of dried, size selected nano-particles made from aqueous solution droplets of MgCl and CaCl, respectively, and compare experimentally derived values with results from state-of-the-art thermodynamic modelling. It is characteristic of both MgCl and CaCl salts that they bind water in the form of hydrates under a range of ambient conditions. We discuss how hydrate formation affects the particles' water uptake and provide an expression for hydrate correction factors needed in calculations of hygroscopic growth factors, critical super-saturations, and derived κ values of particles containing hydrate forming salts. We demonstrate the importance of accounting for hydrate forming salts when predicting hygroscopic properties of sea spray aerosol.
镁和氯化钙盐通过海雾和矿物尘的排放而对全球大气气溶胶负担做出贡献。它们对气溶胶吸湿性和云形成潜力的影响很重要，但由于文献中报告的结果存在不确定性，因此尚不确定。为了解决这个问题，我们对分别由 MgCl 和 CaCl 的水溶液液滴制成的干燥、尺寸选择的纳米颗粒的吸湿性生长和临界过饱和度进行了测量，并将实验得出的数值与最先进的热力学模型的结果进行了比较。这两种盐的特点是，在一系列环境条件下，它们以水合物的形式结合水。我们讨论了水合物的形成如何影响颗粒的吸水，并提供了一个表达式，用于计算含有水合盐的颗粒的吸湿性生长因子、临界过饱和度和衍生κ值所需的水合修正因子。我们证明了在预测海雾气溶胶的吸湿性时，考虑水合盐的重要性。
