Rosati Bernadette, Christiansen Sigurd, Dinesen Anders, Roldin Pontus, Massling Andreas, Nilsson E Douglas, Bilde Merete
Department of Chemistry, Aarhus University, 8000, Aarhus C, Denmark.
Division of Nuclear Physics, Lund University, 22100, Lund, Sweden.
Sci Rep. 2021 May 11;11(1):10008. doi: 10.1038/s41598-021-89346-6.
Sea spray aerosol (SSA) contributes significantly to natural aerosol particle concentrations globally, in marine areas even dominantly. The potential changes of the omnipresent inorganic fraction of SSA due to atmospheric ageing is largely unexplored. In the atmosphere, SSA may exist as aqueous phase solution droplets or as dried solid or amorphous particles. We demonstrate that ageing of liquid NaCl and artificial sea salt aerosol by exposure to ozone and UV light leads to a substantial decrease in hygroscopicity and cloud activation potential of the dried particles of the same size. The results point towards surface reactions on the liquid aerosols that are more crucial for small particles and the formation of salt structures with water bound within the dried aerosols, termed hydrates. Our findings suggest an increased formation of hydrate forming salts during ageing and the presence of hydrates in dried SSA. Field observations indicate a reduced hygroscopic growth factor of sub-micrometre SSA in the marine atmosphere compared to fresh laboratory generated NaCl or sea salt of the same dry size, which is typically attributed to organic matter or sulphates. Aged inorganic sea salt offers an additional explanation for such a measured reduced hygroscopic growth factor and cloud activation potential.
海喷雾气溶胶（SSA）对全球自然气溶胶颗粒浓度有显著贡献，在海洋区域甚至占主导地位。由于大气老化导致的无处不在的SSA无机部分的潜在变化在很大程度上尚未得到探索。在大气中，SSA可能以水相溶液滴或干燥的固体或无定形颗粒的形式存在。我们证明，通过暴露于臭氧和紫外线下使液态氯化钠和人工海盐气溶胶老化，会导致相同尺寸的干燥颗粒的吸湿性和云激活潜力大幅降低。结果表明，液态气溶胶上的表面反应对小颗粒更为关键，并且在干燥的气溶胶中形成了结合有水的盐结构，称为水合物。我们的研究结果表明，老化过程中形成水合物的盐的形成增加，并且干燥的SSA中存在水合物。实地观测表明，与新鲜实验室生成的相同干燥尺寸的氯化钠或海盐相比，海洋大气中亚微米SSA的吸湿生长因子降低，这通常归因于有机物或硫酸盐。老化的无机海盐为这种测量到的吸湿生长因子和云激活潜力降低提供了另一种解释。
