Segregation of NaBr in NaBr/NaCl crystals grown from aqueous solutions: Implications for sea salt surface chemistry

Surface segregation of NaBr in mixed NaBr/NaCl crystals precipitated from aqueous solutions containing Br is investigated. Crystals were grown from solutions of a wide range of Br:Cl values and studied using x‐ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy‐dispersive x‐ray fluorescence (EDX), and atomic force microscopy (AFM). Results indicate that NaBr surface‐segregates to cover 4–5% of the surface at the Br:Cl value found in sea water (1:660). The surface NaBr:NaCl values are ∼35 times higher those of the bulk crystals. The surface NaBr forms domains of average size 635 nm × 635 nm × 53 nm. Large areas of the surface contain NaCl with no detectable NaBr. Complete surface segregation of all Br found in sea salt particles is likely to occur, thereby making a greater amount of Br available for surface reactions with gas‐phase constituents than would be predicted based on bulk composition.