Temperature dependent halogen activation by N<sub>2</sub>O<sub>5</sub> reactions on halide-doped ice surfaces

Abstract

Abstract. We examined the reaction of N 2 O 5 on frozen halide salt solutions as a function of temperature and composition using a coated wall flow tube technique coupled to a chemical ionization mass spectrometer (CIMS). The molar yield of photo-labile halogen compounds was near unity for almost all conditions studied, with the observed reaction products being nitryl chloride (ClNO 2 ) and/or molecular bromine (Br 2 ). The relative yield of ClNO 2 and Br 2 depended on the ratio of bromide to chloride ions in the solutions used to form the ice. At a bromide to chloride ion molar ratio greater than 1/30 in the starting solution, Br 2 was the dominant product otherwise ClNO 2 was primarily produced on these near pH-neutral brines. We demonstrate that the competition between chlorine and bromine activation is a function of the ice/brine temperature presumably due to the preferential precipitation of NaCl hydrates from the brine below 250 K. Our results provide new experimental confirmation that the chemical environment of the brine layer changes with temperature and that these changes can directly affect multiphase chemistry. These findings have implications for modeling air-snow-ice interactions in polar regions and likely in polluted mid-latitude regions during winter as well.

Fine particle pH and the partitioning of nitric acid during winter in the northeastern United States

“…2.1.3. CIMS One-second HNO 3 concentrations were quantified by a high-resolution time of flight chemical ionization mass spectrometer (CIMS), which used the I À reagent ion to selectively detect HNO 3 [Slusher et al, 2004;Lopez-Hilfiker et al, 2012;Lee et al, 2014;Lopez-Hilfiker et al, 2016]. In a heated teflon flow tube at low pressure, iodide ions are produced to selectively cluster with HNO 3 in ambient air.…”

ClNO2 Yields From Aircraft Measurements During the 2015 WINTER Campaign and Critical Evaluation of the Current Parameterization

“…Previous studies have reported evidence of a competition between particle-phase chloride and halogens. For example, enhanced Br 2 formation relative to ClNO 2 has been observed on ice at Cl À :Br À ratios <30 (Lopez-Hilfiker et al, 2012). In addition, reaction of N 2 O 5 with dilute NaI and NaBr solutions has shown production of BrNO 2 , Br 2 , and I 2 (e.g., Behnke et al, 1994;Schweitzer et al, 1998).…”

Flight Deployment of a High‐Resolution Time‐of‐Flight Chemical Ionization Mass Spectrometer: Observations of Reactive Halogen and Nitrogen Oxide Species

“…The output of the 15 N 2 O 5 generation system was verified utilizing two independently-calibrated total nitrogen oxide (NO y ) instruments (National Oceanic and Atmospheric Administration Cavity Ring-down Spectroscopy, NOAA CRDS; Wagner et al, 2011;Wild et al, 2014; and University of California Berkeley thermal dissociation laser-induced fluorescence, TD-LIF; Day et al, 2002;Wooldridge et al, 2010), which agreed to within 1.3%, well within the uncertainties of each technique. The 15 N 2 O 5 was periodically converted to nitryl chloride (Cl 15 NO 2 ) using a wetted salt bed (Kercher et al, 2009;Lopez-Hilfiker et al, 2012). The resulting sample containing Cl 15 NO 2 , H 15 NO 3 , and 15 N 2 O 5 was measured by the HRToF-CIMS and quantified as a sum by the two NO y instruments.…”