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Experimental rainwater divalent mercury speciation and photoreduction rates in the presence of halides and organic carbon

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Author Yang Xu, Jiskra Martin, Sonke Jeroen E.,
Project Seasonal impact of vegetation on atmospheric elemental mercury dry deposition
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Original article (peer-reviewed)

Journal Science of The Total Environment
Volume (Issue) 697
Page(s) 133821 - 133821
Title of proceedings Science of The Total Environment
DOI 10.1016/j.scitotenv.2019.133821

Open Access

URL https://edoc.unibas.ch/73187/
Type of Open Access Green OA Embargo (Freely available via Repository after an embargo)

Abstract

Mercury (Hg) photochemical redox reactions control atmospheric Hg lifetime and therefore play an important role in global Hg cycling. Oxidation of Hg(0) to Hg(II) is currently thought to be a Br-initiated two-stage reaction with end-products HgBr2, HgBrOH, HgBrONO, HgBrOHO. Atmospheric photoreduction of these Hg(II) compounds can take place in both the gas and aqueous phase. Here we present new experimental observations on aqueous Hg(II) photoreduction rates in the presence of dissolved organic carbon and halides and compare the findings to rainfall Hg(II) photoreduction rates. The pseudo first-order, gross photoreduction rate constant, kred, for 0.5 μM Hg(II) in the presence of 0.5 mg L-1 of dissolved organic carbon (DOC) is 0.23 h-1, which is similar to the mean kred (0.15±0.01 h-1(σ, n = 3)) in high altitude rainfall and at the lower end of the median kred (0.41h-1, n=24) in continental and marine waters. Addition of bromide (Br-) to experimental Hg(II)-DOC solutions progressively inhibits Hg(II) photoreduction to reach 0.001 h-1 at total Br- of 10 mM. Halide substitution experiments give Hg(II)Xn (n-2) photoreduction rate constants of 0.016, 0.004 h-1, and
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