Dissociation of Mercuric Oxides Drives Anomalous Isotope Fractionation during Net Photo-oxidation of Mercury Vapor in Air,Environmental Science & Technology

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Dissociation of Mercuric Oxides Drives Anomalous Isotope Fractionation during Net Photo-oxidation of Mercury Vapor in Air
Environmental Science & Technology ( IF 10.8 ) Pub Date : 2022-08-12 , DOI: 10.1021/acs.est.2c02722
Guangyi Sun ₁ , Xinbin Feng _{1,

2} , Runsheng Yin ₃ , Feiyue Wang ₄ , Che-Jen Lin _{1,

5} , Kai Li _{1,

6} , Jonas Olof Sommar ₁

Affiliation

The atmosphere is the primary medium for long-distance transport and transformation of elemental mercury (Hg), a potent neurotoxin. The recent discovery of mass-independent fractionation (MIF) of even-mass Hg isotopes (even-MIF, measured as Δ²⁰⁰Hg and Δ²⁰⁴Hg) in the atmosphere is surprising and can potentially serve as a powerful tracer in understanding Hg biogeochemistry. Far-ultraviolet (UVC) light-induced gas-phase reactions have been suspected as a likely cause for even-MIF, yet the mechanism remains unknown. Here, we present the first experimental evidence of large-scale even-MIF caused by UVC-induced (wavelength: 254 nm) Hg oxidation in synthetic air at the pressure (46–88 kPa) and temperature (233–298 K) resembling those of the lower atmosphere. We observe negatively correlated Δ²⁰⁰Hg and Δ²⁰⁴Hg signatures with values as low as −50‰ and as high as 550‰, respectively, in the remaining atomic Hg pool. The magnitude of even-MIF signatures decreases with decreasing pressure with the Δ²⁰⁰Hg/Δ²⁰⁴Hg ratio being similar to that observed in global precipitation. This even-MIF can be explained by photodissociation of mercuric oxides that are photochemically formed in the UVC-irradiated Hg–O₂ system. We propose that similar processes occurring in the atmosphere, where mercuric oxide species serve as intermediates, are responsible for the observed even-MIF in the environment.

中文翻译：

在空气中汞蒸气的净光氧化过程中，氧化汞的解离驱动异常同位素分馏

大气是元素汞（Hg）（一种强效神经毒素）长距离运输和转化的主要介质。最近发现的均匀质量 Hg 同位素（even-MIF，测量为 Δ ²⁰⁰ Hg 和 Δ ^{204 ）的质量无关分馏 (MIF)}大气中的 Hg) 令人惊讶，并可能成为了解 Hg 生物地球化学的强大示踪剂。远紫外线 (UVC) 光诱导的气相反应被怀疑是偶数 MIF 的可能原因，但其机制仍然未知。在这里，我们提出了由 UVC 诱导（波长：254 nm）在合成空气中在压力（46-88 kPa）和温度（233-298 K）下引起的大规模偶数 MIF 氧化的第一个实验证据，类似于那些的低层大气。我们在剩余的原子汞库中观察到负相关的 Δ ²⁰⁰ Hg 和 Δ ²⁰⁴ Hg 特征，其值分别低至 -50‰ 和高达 550‰。^{随着 Δ 200} Hg/Δ ²⁰⁴压力的降低，偶数 MIF 特征的幅度减小Hg 比率与全球降水中观察到的相似。_{这种偶数 MIF 可以通过在 UVC 照射的 Hg-O 2}系统中光化学形成的氧化汞的光解来解释。我们提出，在大气中发生的类似过程，其中氧化汞物质作为中间体，是环境中观察到的偶数 MIF 的原因。

更新日期：2022-08-12

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