Oxidation and Reduction of Atmospheric Mercury

化学系的环境化学科学计划资助纽约州立大学环境科学和林业学院的Theodore Dibble教授研究汞的化学。汞是一种神经毒素，在许多鱼类中积累到有毒水平，这就是为什么卫生机构建议限制鱼类消费。为了确定限制人类活动中汞排放的量，科学家们致力于了解汞是如何在空气和土壤之间转移到鱼类生活的水中的。当汞以汞化合物的形式从空气中进入土壤和水中时，效率最高。然而，汞主要以汞原子的形式进入空气中。一旦在空气中，汞原子可以反应形成汞化合物，但这些化合物可能会分解，重新形成汞原子。为了了解汞从空气到土壤和水的转移，我们需要知道汞原子形成化合物的反应，以及这些化合物如何打破化学键重新生成汞原子。迪布尔教授通过计算来研究汞在气相中的反应，这些计算产生了化学反应的能量学和速率信息。除了对环境的潜在社会影响，该项目还为一名研究生、一名博士后和几名本科生提供了研究机会。这个项目的第一个假设是，HOHg自由基(由汞和OH反应形成)与臭氧的反应速度很快，使OH自由基能够在大部分大气中引发汞(0)氧化成汞(II)。第二个假设是，与许多大气模型中的假设相反，汞与臭氧的直接反应不会在气态大气中引发汞(0)的氧化。第三种假设是，虽然许多汞(II)化合物的光解速度很快，但它往往会使汞处于汞(II)的氧化态，而不是将其还原为汞(0)或汞(I)。对这个项目很重要的大多数化合物或反应都没有实验数据。这项研究使用量子化学和计算动力学来检验这些假说。具体地说，该团队确定了含汞自由基关键反应的热力学和速率常数，并计算了稳定的汞(II)化合物的吸收截面和光解路径。这些结果被纳入大气波动模型。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The Environmental Chemical Sciences Program in the Division of Chemistry funds Professor Theodore Dibble at SUNY College of Environmental Science and Forestry for studies of the chemistry of mercury. Mercury is a neurotoxin that accumulates to toxic levels in many fish species, which is why health agencies recommend limits on fish consumption. In order to determine how much to limit mercury emissions from human activities, scientists work to understand how mercury is transferred between air and soil to the water in which fish live. Mercury enters soil and water from the air most efficiently when it is in the form of mercury compounds. However, mercury mostly enters the air as atoms of mercury. Once in the air, atoms of mercury can react to form mercury compounds, but those compounds may break up to re-form mercury atoms. To understand the transfer of mercury from air to soil and water, we need to know both the reactions by which mercury atoms form compounds and how those compounds break chemical bonds to regenerate atoms of mercury. Professor Dibble studies the reactions of mercury in the gas phase by performing calculations which yield information on the energetics and rates of chemical reactions. in addition to the potential societal impacts in environment, this project provides research opportunities for a graduate student, a postdoc, and several undergraduate students. The first hypothesis of this project is that the reaction of HOHg radical (formed by the reaction of Hg with OH) with ozone is fast, enabling OH radical to initiate oxidation of Hg(0) to Hg(II) throughout most of the atmosphere. The second hypothesis is that direct reaction of Hg with ozone does not initiate Hg(0) oxidation in the gaseous atmosphere, contrary to what is assumed in many atmospheric models. The third hypothesis is that while photolysis of many Hg(II) compounds is fast, it often leaves mercury in the Hg(II) oxidation state rather than reducing it to Hg(0) or Hg(I). No experimental data exist on most of the compounds or reactions important to this project. This research uses quantum chemistry and computational kinetics to test these hypotheses. Specifically, the team determines the thermodynamics and rate constants for key reactions of Hg-containing radicals, and computes absorption cross-sections and photolysis pathways for stable Hg(II) compounds. These results are incorporated into models of atmospheric mercury.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.