Impact of SO2 and light on chemical morphology and hygroscopicity of natural salt aerosols

The interactions between SO2 and natural salt aerosol particles represent complex and crucial dynamics within atmospheric processes and the broader climate system. This study investigated the SO2 uptake, hygroscopicity, morphology and mixing states of natural salt particles, which are generated from brines sampled from the Chaka salt lake located in the Qinghai -Tibet plateau. A comparison with atomized pure NaCl particles is included as reference. The results show that NaCl particles exhibit the lowest SO2 uptake, while Chaka salt particles demonstrate higher uptake due to their complex composition. The hygroscopicity of salt particles is influenced by several factors, including chemical complexity, SO2 exposure and light conditions. In comparison to pure NaCl, Chaka salt displays higher hygroscopicity, which is further enhanced in the presence of SO2. However, when exposed to light, mass growth is suppressed, suggesting the formation of species with lower hygroscopicity, such as Na2SO4. Analysis of particle morphology and mixing states reveals notable distinctions between NaCl crystals and Chaka salt particles, where the Chaka salt particles exhibit rounded shapes with a structure composed of cubic NaCl cores surrounded by sulfate materials as a coating. In addition, the chemical morphology analysis also reveals that the particles show morphological and spectral changes before and after the exposure to SO2, light and high RH. Therefore, this research highlights the intricate interactions between SO2 and natural salt aerosol particles in diverse environmental settings, underscoring their multifaceted impacts on atmospheric processes.