Temperature and Concentration Affect Particle Size Upon Sublimation of Saline Ice: Implications for Sea Salt Aerosol Production in Polar Regions

• Published in: Geophysical research letters 2022-04, Vol.49 (8), p.n/a
• Main Authors: Závacká, Kamila, Neděla, Vilém, Olbert, Martin, Tihlaříková, Eva, Vetráková, Ľubica, Yang, Xin, Heger, Dominik
• Format: Article
• Language: English
• Subjects: Aerosol production; Aerosols; Atmospheric chemistry; Atmospheric radiation; Bromine; bromine explosion; Chemical compounds; Coastal zone; Crystals; Downward long wave radiation; eutectic temperature; Global climate; Low temperature; microscopy; Ozone; Ozone depletion; Physical factors; Polar environments; Polar regions; Salt; Salt particles; Salts; Scanning electron microscopy; Sea ice; sea salt aerosols; Sublimation; Subzero temperature; Temperature; Temperature dependence
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL097098

Using an environmental scanning electron microscope, we quantified for the first time aerosol‐sized salt particles formed during the sublimation of sea ice as a function of temperature and concentration. The sublimation temperature of the ice is a dominating physical factor to determine the size of the residua: Below −20°C, micron‐sized pieces of salt emerge, whereas above the temperature large chunks of salt are detected. Another such aspect influencing the distribution of sizes in salt particles is the concentration: Micron‐sized particles are observed exclusively at salinities below 3.5 psu, while below 0.085 psu particles with a median smaller than 6 μm arise from sea ices at any subzero temperature. Moreover, when a chunk of salt sublimes at less than −30°C to be dried and warmed later, a large number of sub‐micron crystals will appear. We relate our findings to the production of the polar atmospheric sea salt aerosols. Plain Language Summary In polar regions, saline ices on sea ice or at coastal areas are thought to be a direct source of chemical compounds and sea salt aerosols; these salty aerosols are important to polar atmospheric chemistry and global climate for various reasons, such as that they affect atmospheric radiation in both a direct and an indirect manner. However, the exact location of the salts within the ice, together with the temperature and concentration dependence of the size and number density of the salt particles formed, was previously poorly understood and not well quantified. We therefore utilized a unique electron microscope to observe the structural changes occurring when saline ices sublime to create salt particles. Our experiments showed that small salt particles, proxies of sea salt aerosols, are preferably generated from low‐concentrated ices and at low temperatures. These microscopic observations provide direct laboratory evidence to the proposed mechanism of sea salt aerosol production from sublimating saline ice and snow and may help us to fit the missing piece of information into the puzzle of polar spring ozone depletion and bromine explosion events. Key Points The size distribution and numerical density of salt particles formed from sublimating salty ices were quantified for the first time Micrometer‐sized particles arise from low salinity ices (100 μm particles are produced by sublimation above −21 °C in ices above 0.85 psu, and at an