Effects of wind speed on water uptake, phase state, and viscosity of sea spray aerosols

Abstract

This study investigates the effects of wind speed on physicochemical properties such as water uptake, phase state, and viscosity at varying relative humidity (RH) of individual nascent sea spray aerosols (SSAs). We examined SSA sized within 0.1-0.6 mu m generated from a wind-wave channel at two wind speeds: 10 m/s representing a wind lull scenario over the ocean and 19 m/s corresponding to wind speeds encountered in stormy conditions. Atomic force microscopy (AFM) was utilized to study two predominant SSA morphologies: core-shell and rounded. AFM phase state measurements at 60% RH revealed that shells of core-shells at 19 m/s were largely liquid, while those at 10 m/s were mostly semisolid or liquid with similar proportions, where semisolid shells exhibited higher viscosities at lower wind speed. Rounded SSAs were predominantly liquid or semisolid at 60% RH, with similar semisolid viscosities for both wind speeds. Increased water uptake was observed for core-shells at 19 m/s, while rounded SSA had similar hygroscopicity between the two wind conditions. Collectively, we observed a variation in the physicochemical properties of SSA generated at two wind speeds, which can be attributed to the impact of elevated wind speed on disrupting the sea surface microlayer film structure and composition.