Sublimation of frozen CsCl solutions in ESEM: determining the number and size of salt particles relevant to sea-salt aerosols

Abstract

Abstract. We identified the factors that, during the sublimation of a frozen CsCl solution, are important in generating fine salt particles as a possible source of salt aerosol. The number, size, and structure of the particles that remain after ice sublimation were investigated with respect to the concentration of the salt in the sample, the freezing method, and the sublimation temperature. The last-named aspect is evidently of primary importance for the preference of fine salt crystals over a large compact piece of salt. Independently of the concentration and freezing method tested, the sublimation of the frozen samples above the eutectic temperature (Teu) yielded a large compact piece of salt, namely, an improbable source of aerosol particles. Small salt particles that might be a source of atmospheric aerosols were formed predominantly at the temperatures below Teu, and their structures strongly depended on the concentration of the salt. For example, the sublimation of those samples that exhibited less than 8 psu (0.05 M) often produced small aerosolizable isolated particles readily able to be windblown. Conversely, the sublimation of 78 psu (0.5 M) samples led to the formation of relatively stable and largely interconnected salt structures. Presumably, our findings have important implications because the formed salt particles may assume the role of cloud condensation nuclei and ice-nucleating particles, affect polar atmospheric radiative forcing, and facilitate heterogeneous atmospheric chemistry.