Hygroscopic behavior and aerosol chemistry of atmospheric particles containing organic acids and inorganic salts

Aerosol hygroscopic behavior plays a central role in determining climate effects and environmental influence of atmospheric particulates. Water-soluble organic acids (WSOAs) constitute a significant fraction of organic aerosols. These organic acids have a complex impact on aerosol hygroscopicity due to their physical and chemical interactions with atmospheric inorganic salts. The mixing of WSOAs with inorganic salts exerts a multiple influence on the hygroscopic growth and phase behaviors of aerosol particles, largely depending on the composition ratio, acid properties, particle size and interactions between particle components. The WSOAs play a critical role in determining water uptake characteristics of aerosol particles, especially in the low and moderate RH ranges. The previous studies reveal the occurrence of aerosol chemistry related to chloride/nitrate/ammonium depletions in aerosol droplets containing WSOAs and inorganic salts. The potential influence of WSOAs on the atmospheric recycling of HCl/HNO3/NH3 due to the chloride/nitrate/ammonium depletion may contribute to the atmospheric budget of reactive gases. A fundamental understanding for the hygroscopic behavior and aerosol chemistry of inorganic-WSOA systems is essential for the accurate parameterization of aerosol behaviors in atmospheric models. However, there is still lack of a comprehensive understanding of the hygroscopicity and related aerosol chemistry of internally mixed inorganic-WSOA systems. The present review comprehensively summarizes the impacts of WSOAs on hygroscopicity and phase changes of atmospherically relevant inorganic salts in aerosol particles especially under subsaturated conditions, and overviews the recent advances on aerosol chemistry related to the hygroscopic process for the internally mixed inorganic-WSOA aerosols.