Fig. 3: Evaluation of sea salt aging process.

The elemental composition of bulk particles was determined with CCSEM/EDX for all particles (2022) assigned as “sea salt” (See Supplementary Fig. 1); the ratios of Cl/(Na+0.5Mg) were calculated, where the dashed line indicates the characteristic ratio of unprocessed (i.e., fresh) sea salt particles. The values of (Cl+N + 0.5 S)/(Na+0.5Mg) correspond to aged sea salt particles with chloride quantitatively displaced by only nitrate and sulfate.