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

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 Br 2 and BrCl were formed, with the Br 2 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.

Production of gas phase NO2 and halogens from the photolysis of thin water films containing nitrate, chloride and bromide ions at room temperature

“…60,69,70,[123][124][125][126][127][128][129][130][131][132] Results by Frinak and Abbatt 60 showed that when NaCl-NaBr mixtures were oxidized by gas phase OH, Cl 2 was not produced until Br (Fig. 7a-c).…”

An overview of current issues in the uptake of atmospheric trace gases by aerosols and clouds

“…Simulations of molecules interacting with the vapour/liquid interface of water have been performed for a variety of molecular species, (Pohorille and Benjamin, 1991;Matsumoto et al, 1993;Pohorille and Benjamin, 1993;Matsumoto, 1996;Sokhan and Tildesley, 1996;Tarek et al, 1996a, b;Taylor et al, 1997;Wilson and Pohorille, 1997;Benjamin, 1999;Taylor and Garrett, 1999;Dang and Feller, 2000;Shin and Abbott, 2001;Roeselova et al, 2003;Morita, 2003;Dang and Garrett, 2004;Paul and Chandra, 2004;Roeselova et al, 2004;Vacha et al, 2004;Vieceli et al, 2005;Canneaux et al, 2006;Minofar et al, 2007;Partay et al, 2007;Carignano et al, 2008;Mahiuddin et al, 2008;Morita and Garrett, 2008;Miller et al, 2009;Patel et al, 2009;Sun et al, 2009) including hydrophilic species such as ethanol, acids including oxalic and citric, amphiphilic molecules such as peptides, hydrophobic species such as oxygen and nitrogen, and radical species such as OH and HO 2 . The condensation of water on aqueous droplets is a special case of molecular uptake, but for molecular simulations, which treat all molecules as distinguishable, the methods used are the same as for other molecular species.…”

Reactions at surfaces in the atmosphere: integration of experiments and theory as necessary (but not necessarily sufficient) for predicting the physical chemistry of aerosols

“…79 This is faster by about two orders of magnitude than the reaction of OH with solid NaCl. [80][81][82][83] Experimental evidence for this interface reaction was based primarily on much greater (by a factor of B10 3 ) gas phase Cl 2 production than could be quantitatively predicted by treating uptake and reaction of OH by the conventional mechanism. However, the exact mechanism remains to be elucidated.…”