Observed size-dependent effect of the marine air on aerosols hygroscopicity at a coastal site of Shenzhen, China

Aerosols hygroscopicity and CCN activity in coastal area is influenced by continental-marine air interaction, probably exerting a profound climate effect. In this study, combining field measurement at a coastal site in Shenzhen with a back trajectory model, we have identified an externally-mixed sea salt mode in accumulated particles, where the hygroscopic parameter (κ) ranges from 0.97 to 1.14. The sea salt mode, however, was not observed for ultrafine particles in nucleation/Aitken modes. Nonetheless, the. hygroscopicity of the particles across all sizes under the influence of marine air were remarkably enhanced by 49 %–64 % compared to the continental air masses. Moreover, we reveal a considerable transport of marine-sourced sulfate aerosols when the marine air dominated, explaining the enhanced hygroscopicity. We attribute the absence of externally-mixed sea salt in nucleation/Aitken modes to that the ultrafine marine-sourced aerosols are generally with lower quantity and tend to be collided and internally-mixed during transport. We finally made a global review using observations at 21 sites, deriving the κ of 0.21–0.25, 0.23–0.32, and 0.51–0.60 categorized by continental, coastal, and oceanic respectively. Our study illustrates the size-dependent effect of the continental-marine air interaction on particles hygroscopicity and provides observational basis for model simulation. [Display omitted] •Particle hygroscopicity increased by 49%–64% during marine air masses compared to continental air masses.•The externally-mixed sea salt was observed in accumulated particles but not in nucleation/Aitken modes.•The aerosols hygroscopicity measured at 21 sites was analyzed by continent, coastal, and oceanic types.