Hygroscopic property of inorganic salts in atmospheric aerosols measured with physisorption analyzer

Hygroscopicity is capable of significantly affecting atmospheric visibility, radiative forcing, and cloud condensation nuclei process. Herein, a physisorption analyzer was adopted to determine the hygroscopicity of inorganic salt particles in atmospheric aerosols (e.g., NaNO₃, NaClO₄, MgSO₄, K₃PO₄, K₂HPO₄, and KH₂PO₄) at 298 K. By regulating the ambient relative humidity (RH), qualitative and quantitative information of the mentioned particles in humidifying and dehumidifying cycles was acquired. The deliquescence relative humidity (DRH) and efflorescence relative humidity (ERH) were measured, and supersaturation was observed and recorded during the dehumidification process. The water-to-salt molar ratios (WSR) of the mentioned inorganic salts depending on RH were determined, and the hygroscopic results of NaNO₃ and NaClO₄ particles were well consistent with the results achieved with other methods or by theoretical prediction. This study fitted WSR-to-RH equations suitable for NaNO₃, NaClO₄, MgSO₄, K₃PO_4, and K₂HPO₄ particles. The adsorption heats for monolayer water molecules in the mentioned inorganic salt particles are calculated. The present study lays a solid foundation for gaining insights into the effects of RH on atmospheric aerosols.