Release of gas-phase halogens from sodium halide substrates: heterogeneous oxidation of frozen solutions and desiccated salts by hydroxyl radicals: Fid-Bau Portal

Release of gas-phase halogens from sodium halide substrates: heterogeneous oxidation of frozen solutions and desiccated salts by hydroxyl radicals

S J Sjostedt / J P D Abbatt

Abstract

Motivated by the need to determine the mechanism of the initial release of halogens from sea ice and marine aerosol substrates, a study of the interactions of OH radicals with a variety of halide-containing surfaces has been performed in a coated-wall flow tube using chemical ionization mass spectrometry for gas-phase analysis. The salts studied were NaCl with 0.01% and 0.002% impurities of Br⁻ and I⁻ respectively, and NaCl/NaBr mixtures with Cl⁻/Br⁻ seawater ratios. The surfaces were desiccated salts, desiccated salts exposed to elevated relative humidity, and frozen solutions. In all cases, gas-phase Br₂ and BrCl were formed, with the Br₂ yield (defined as a molar ratio of halogen produced to OH lost) larger than 0.2 and the BrCl yield as roughly 0.01. For the first time, an observation of heterogeneous release of iodine-containing halogens (in particular IBr) was made with yields comparable to those of BrCl. We note that pH neutral frozen solutions demonstrated halogen release, although the yields were higher for acidic frozen solutions.