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Mass-Independent Fractionation of Even and Odd Mercury Isotopes during Atmospheric Mercury Redox Reactions

Fu, Xuewu and Jiskra, Martin and Yang, Xu and Marusczak, Nicolas and Enrico, Maxime and Chmeleff, Jérôme and Heimbürger-Boavida, Lars-Eric and Gheusi, François and Sonke, Jeroen E.. (2021) Mass-Independent Fractionation of Even and Odd Mercury Isotopes during Atmospheric Mercury Redox Reactions. Environmental science & technology, 55 (14). pp. 10164-10174.

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Abstract

Mass-independent fractionation (MIF) of stable even mass number mercury (Hg) isotopes is observed in rainfall and gaseous elemental Hg; 0; globally and is used to quantify atmospheric Hg deposition pathways. The chemical reaction and underlying even-Hg MIF mechanism are unknown however and speculated to be caused by Hg photo-oxidation on aerosols at the tropopause. Here, we investigate the Hg isotope composition of free tropospheric Hg; 0; and oxidized Hg; II; forms at the high-altitude Pic du Midi Observatory. We find that gaseous oxidized Hg has positive Δ; 199; Hg, Δ; 201; Hg, and Δ; 200; Hg and negative Δ; 204; Hg signatures, similar to rainfall Hg, and we document rainfall Hg Δ; 196; Hg to be near zero. Cloud water and rainfall Hg show an enhanced odd-Hg MIF of 0.3‰ compared to gaseous oxidized Hg; II; , potentially indicating the occurrence of in-cloud aqueous Hg; II; photoreduction. Diurnal MIF observations of free tropospheric Hg; 0; show how net Hg; 0; oxidation in high-altitude air masses leads to opposite even- and odd-MIF in Hg; 0; and oxidized Hg; II; . We speculate that even-Hg MIF takes place by a molecular magnetic isotope effect during Hg; II; photoreduction on aerosols that involves magnetic halogen nuclei. A Δ; 200; Hg mass balance suggests that global Hg deposition pathways in models are likely biased toward Hg; II; deposition. We propose that Hg cycling models could accommodate the Hg-isotope constraints on emission and deposition fluxes.
Faculties and Departments:05 Faculty of Science > Departement Umweltwissenschaften > Geowissenschaften > Umweltgeowissenschaften (Alewell)
UniBasel Contributors:Jiskra, Martin
Item Type:Article, refereed
Article Subtype:Research Article
ISSN:1520-5851
Note:Publication type according to Uni Basel Research Database: Journal article
Language:English
Identification Number:
edoc DOI:
Last Modified:13 Oct 2021 15:50
Deposited On:13 Oct 2021 15:50

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