01 Jun 2022
01 Jun 2022
Status: this preprint is currently under review for the journal ACP.

Evidence for mass independent fractionation of even mercury isotopes in the troposphere

Shuyuan Huang1,2, Yunlong Huo1, Heng Sun1, Supeng Lv1, Yuhan Zhao1,2, Kunning Lin1, Yaojin Chen2, and Yuanbiao Zhang1 Shuyuan Huang et al.
  • 1Third Institute of Oceanography, Ministry of Natural Resources, Xiamen, Fujian 361005, China
  • 2State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, Fujian 361102, China

Abstract. Mass independent fractionation (MIF) of even mercury (Hg) isotopes has long been observed in atmospheric related samples and is confirmed to be generated in the atmosphere, but its exact mechanism is covered up by the Hg sources and atmospheric transformations and stays unclear. Here, we present the first Hg isotope compositions of particulate bound mercury (PBM) in the Northwest Pacific and observe highly positive Δ200Hg values (up to 0.42 ‰). The MIF signatures are mainly controlled by photoreduction, gaseous elemental mercury (GEM) oxidation, and even-MIF dominated oxidation processes. Mercury in a small part of samples influenced by anthropogenic emissions is recognized by Hg concentrations and Δ199Hg signatures. The correlation between Δ200Hg and light conditions confirms that even-MIF is linked to photochemical reactions. The correlation between Δ200Hg and altitudes suggests that a max even-MIF signatures existed in the troposphere. We use Δ199Hg/Δ200Hg ratios and ternary isotopic mixing model to estimate the contributions of photoreduction, GEM oxidation and even-MIF dominated oxidation. Our results demonstrate that atmospheric transformations are far more important than Hg sources in shifting Hg isotope compositions of PBM samples, especially in the marine boundary layer of the open ocean, which is characterized by less anthropogenic influences and has implications for our understanding of the mechanism of even-MIF and subsequently Hg behaviors in the atmosphere.

Shuyuan Huang et al.

Status: open (until 13 Jul 2022)

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  • RC1: 'Comment on acp-2022-284', Anonymous Referee #2, 21 Jun 2022 reply

Shuyuan Huang et al.

Shuyuan Huang et al.


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Short summary
The Hg sources and atmospheric transformations in the marine boundary layer of the open ocean is revealed by Hg stable isotopes. Anthropogenic emissions are responsible for high Hg concentrations, while photoreduction of Hg(II) and Hg(0) oxidation play important role in shifting Hg isotopic compositions. Mass independent fractionation signatures are useful in quantifying contributions of various atmospheric transformations of Hg.