Deposition and Reduction of Oxidized Mercury on the Ice Surface: Quantum-Chemical Study and Implication of Mercury Activities in the Arctic
Deposition and Reduction of Oxidized Mercury on the Ice Surface: Quantum-Chemical Study and Implication of Mercury Activities in the Arctic
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DOI：
10.1021/acs.jpcc.2c07879
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发表时间：
2023-01
期刊：
影响因子：
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通讯作者：
Logan Vogelsong;J. Fuentes;A. Asaduzzaman
中科院分区：
文献类型：
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作者：
Logan Vogelsong;J. Fuentes;A. Asaduzzaman
汞以原子态Hg（0）释放到大气中，在紫外线下被氧化形成氧化的汞分子，例如XHgY、BrHgOx、BrHgXO、XHgOH、XHgO 2 H和XHgNO2，其中X和Y代表Cl、Br和I原子。这些气态氧化汞物质然后存款到表面上，包括北极的冰雪上。采用第一性原理密度泛函理论研究了氧化汞在冰表面的沉积和还原机理。氧化汞分子的沉积特征是在（0001）冰表面上的吸附。计算得到的吸附能介于−2.33和−4.33 eV之间，证实了汞分子与冰表面之间的强相互作用。此外，包括对每个汞分子的总电子能和熵的热校正，计算0 °C下的吸附吉布斯自由能。计算的吉布斯吸附自由能为负（−1.60至−3.60 eV），这证实了吸附过程的放能性质。此外，冰表面与汞分子之间的强烈相互作用表明汞分子保留在表面上，并验证了先前关于北极春季汞浓度高的研究。除BrHgOBr和BrHgOI外，所有分子都解离吸附在表面上。汞分子的解离导致在表面上形成还原的汞原子。由于单质汞蒸气压低、水溶性差、表面吸附能力弱，汞的表面还原为汞的还原和再排放提供了新的途径。
Mercury is released into the atmosphere as atomic Hg(0) where it is oxidized under ultraviolet light to form oxidized mercury molecules such as XHgY, BrHgOX, BrHgXO, XHgOH, XHgO2H, and XHgNO2, where X and Y represent Cl, Br, and I atoms. These gaseous oxidized mercury species then deposit onto the surface, including on the Arctic ice and snow. The deposition and reduction mechanisms of oxidized mercury on the ice surface are investigated using first-principles density functional theory. Deposition of oxidized mercury molecules is characterized by adsorption on the (0001) ice surface. Calculated adsorption energies between −2.33 and −4.33 eV confirm the strong interaction between mercury molecules and the ice surface. Further, including the thermal corrections to the total electronic energy and entropy for each mercury molecule, the Gibbs free energy of adsorption is calculated at 0 °C. The calculated Gibbs free energy of adsorption is negative (−1.60 to −3.60 eV), which confirms the exoergic nature of adsorption processes. Further, strong interactions between the ice surface and mercury molecules indicate the retention of mercury molecules on the surface and validate the previous studies on the high concentration of Hg during springtime in the Arctic. Other than BrHgOBr and BrHgOI, all molecules are dissociatively adsorbed on the surface. The dissociation of mercury molecules leads to the formation of a reduced Hg atom on the surface. As the elemental mercury has low vapor pressure, low water solubility, and is weakly adsorbed on the surface, the surface reduction of mercury provides a new path for mercury reduction and re-emission into the atmosphere.