气候变化领域集成服务门户(CCPortal): PH-dependent production of molecular chlorine; bromine; and iodine from frozen saline surfaces

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DOI	10.5194/acp-19-4917-2019
	PH-dependent production of molecular chlorine; bromine; and iodine from frozen saline surfaces
	Halfacre J.W.; Shepson P.B.; Pratt K.A.
发表日期	2019
ISSN	16807316
起始页码	4917
结束页码	4931
卷号	19 期号:7
英文摘要	The mechanisms of molecular halogen production from frozen saline surfaces remain incompletely understood, limiting our ability to predict atmospheric oxidation and composition in polar regions. In this laboratory study, condensed-phase hydroxyl radicals (OH) were photochemically generated in frozen saltwater solutions that mimicked the ionic composition of ocean water. These hydroxyl radicals were found to oxidize Cl-, Br-, and I-, leading to the release of Cl2, Br2, I2, and IBr. At moderately acidic pH (buffered between 4.5 and 4.8), irradiation of ice containing OH precursors (either of hydrogen peroxide or nitrite ion) produced elevated amounts of I2. Subsequent addition of O3 produced additional I2, as well as small amounts of Br2. At lower pH (1.7-2.2) and in the presence of an OH precursor, rapid dark conversion of I- to I2 occurred from reactions with hydrogen peroxide or nitrite, followed by substantial photochemical production of Br2 upon irradiation. Exposure to O3 under these low pH conditions also increased production of Br2 and I2; this likely results from direct O3 reactions with halides, as well as the production of gas-phase HOBr and HOI that subsequently diffuse to frozen solution to react with Br- and I-. Photochemical production of Cl2 was only observed when the irradiated sample was composed of high-purity NaCl and hydrogen peroxide (acting as the OH precursor) at pH = 1.8. Though condensed-phase OH was shown to produce Cl2 in this study, kinetics calculations suggest that heterogeneous recycling chemistry may be equally or more important for Cl2 production in the Arctic atmosphere. The condensed-phase OH-mediated halogen production mechanisms demonstrated here are consistent with those proposed from recent Arctic field observations of molecular halogen production from snowpacks. These reactions, even if slow, may be important for providing seed halogens to the Arctic atmosphere. Our results suggest the observed molecular halogen products are dependent on the relative concentrations of halides at the ice surface, as we only observe what diffuses to the air-surface interface. © 2019 Author(s).
语种	英语
scopus关键词	atmospheric chemistry; bromine; chlorine; halogen; hydroxyl radical; iodine; pH; photochemistry; reaction kinetics
来源期刊	Atmospheric Chemistry and Physics
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/144494
作者单位	Department of Chemistry, Indiana University Southeast, New Albany, IN, United States; Department of Chemistry, Purdue University, West Lafayette, IN, United States; Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN, United States; School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, NY, United States; Department of Chemistry and Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI, United States
推荐引用方式 GB/T 7714	Halfacre J.W.,Shepson P.B.,Pratt K.A.. PH-dependent production of molecular chlorine; bromine; and iodine from frozen saline surfaces[J],2019,19(7).
APA	Halfacre J.W.,Shepson P.B.,&Pratt K.A..(2019).PH-dependent production of molecular chlorine; bromine; and iodine from frozen saline surfaces.Atmospheric Chemistry and Physics,19(7).
MLA	Halfacre J.W.,et al."PH-dependent production of molecular chlorine; bromine; and iodine from frozen saline surfaces".Atmospheric Chemistry and Physics 19.7(2019).