Mass-Independent Fractionation of Mercury Isotopes during Photoreduction of Soot Particle Bound Hg(II),Environmental Science & Technology

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Mass-Independent Fractionation of Mercury Isotopes during Photoreduction of Soot Particle Bound Hg(II)
Environmental Science & Technology ( IF 10.8 ) Pub Date : 2021-10-08 , DOI: 10.1021/acs.est.1c02679
Qiang Huang _{1,

2} , Xiaoshuai He ₂ , Weilin Huang ₂ , John R Reinfelder ₂

Affiliation

Soot and mercury (Hg) are two notorious air pollutants, and the fate and transport of Hg may be affected by soot at various scales in the environment as soot may be both a carrier and a reactant for active Hg species. This study was designed to quantify photoreduction of Hg(II) in the presence of soot and the associated Hg isotope fractionation under both atmospheric aerosol and aqueous conditions (water-saturated). Photoreduction experiments were conducted with diesel soot particulate matter under controlled temperature and relative humidity (RH) conditions using a flow-through semibatch reactor system. Mass-dependent fractionation resulted in the enrichment of heavier Hg isotopes in the remaining Hg(II) with enrichment factors (ε²⁰²Hg) of 1.48 ± 0.02‰ (±2 standard deviation) to 1.75 ± 0.05‰ for aerosol-phase reactions (RH 28–68%) and from 1.26 ± 0.11 to 1.50 ± 0.04‰ for aqueous-phase reactions. Positive odd mass-independent fractionation (MIF) was observed in aqueous-phase reactions, resulting in Δ¹⁹⁹Hg values for reactant Hg(II) as high as 5.29‰, but negative odd-MIF occurred in aerosol-phase reactions, in which Δ¹⁹⁹Hg values of reactant Hg(II) varied from −1.02 to 0‰. The average ratio of Δ¹⁹⁹Hg/Δ²⁰¹Hg (1.1) indicated that under all conditions, MIF was dominated by magnetic isotope effects during photoreduction of Hg(II). Increasing RH resulted in higher reduction rates but lower extents of negative MIF in the aerosol-phase experiments, suggesting that the reduction of soot particle-bound Hg(II) was responsible for the observed negative odd-MIF. Our results suggest that mass-independent Hg isotope fractionation during Hg(II) photoreduction varies with soot aerosol water content and that Hg-stable isotope ratios may be used to understand the transformational histories of aerosol-bound Hg(II) in the environment.

中文翻译：

在烟尘粒子束缚 Hg(II) 光还原过程中汞同位素的质量无关分馏

烟尘和汞 (Hg) 是两种臭名昭著的空气污染物，由于烟尘可能既是活性汞物质的载体，也可能是活性物质的反应物，因此汞的归宿和迁移可能会受到环境中各种规模的烟尘的影响。本研究旨在量化在大气气溶胶和水性条件（水饱和）存在烟灰和相关 Hg 同位素分馏的情况下 Hg(II) 的光还原。在受控温度和相对湿度 (RH) 条件下，使用流通式半间歇式反应器系统对柴油机烟灰颗粒物质进行光还原实验。质量相关的分馏导致剩余 Hg(II) 中较重的 Hg 同位素富集，富集因子 (ε ²⁰²Hg) 从 1.48 ± 0.02‰（±2 标准偏差）到 1.75 ± 0.05‰ 气溶胶相反应（RH 28–68%）和从 1.26 ± 0.11 到 1.50 ± 0.04‰ 水相反应。在水相反应中观察到正奇数质量独立分馏（MIF），导致反应物 Hg（II）的Δ ¹⁹⁹ Hg 值高达 5.29‰，但在气溶胶相反应中出现负奇数-MIF，其中 Δ ¹⁹⁹反应物 Hg(II) 的 Hg 值从 -1.02 变化到 0‰。Δ ¹⁹⁹ Hg/Δ ²⁰¹的平均比值Hg (1.1) 表明，在所有条件下，MIF 在 Hg(II) 的光还原过程中受磁同位素效应支配。在气溶胶相实验中，增加 RH 导致更高的减少率，但负 MIF 的程度较低，这表明烟灰颗粒结合 Hg(II) 的减少是观察到的负奇数 MIF 的原因。我们的结果表明，Hg(II) 光还原过程中与质量无关的 Hg 同位素分馏随烟尘气溶胶含水量而变化，并且 Hg 稳定同位素比率可用于了解环境中气溶胶结合 Hg(II) 的转化历史。

更新日期：2021-10-19

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