Oxidation and Reduction of Atmospheric Mercury

化学学部的环境化学科学项目资助纽约州立大学环境科学与林业学院的Theodore Dibble教授进行汞的化学研究。汞是一种神经毒素，在许多鱼类中积累到有毒水平，这就是卫生机构建议限制鱼类消费的原因。为了确定限制人类活动中汞排放的程度，科学家们努力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。汞以汞化合物的形式从空气中进入土壤和水的效率最高。然而，汞主要以汞原子的形式进入空气。一旦进入空气，汞原子就会反应形成汞化合物，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中的转移，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来再生汞原子。Dibble教授通过计算得出化学反应的能量学和速率来研究汞在气相中的反应。除了对环境的潜在社会影响外，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。本项目的第一个假设是HOHg自由基（由Hg与OH反应形成）与臭氧的反应速度很快，使得OH自由基在整个大气中引发Hg(0)氧化为Hg（II）。第二个假设是，与许多大气模型的假设相反，汞与臭氧的直接反应不会引发气态大气中的汞(0)氧化。第三种假设是，虽然许多Hg（II）化合物的光解作用很快，但它通常使汞处于Hg（II）氧化态，而不是还原为Hg(0)或Hg(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。本研究使用量子化学和计算动力学来验证这些假设。具体来说，该团队确定了含Hg自由基关键反应的热力学和速率常数，并计算了稳定Hg（II）化合物的吸收截面和光解途径。这些结果被纳入大气汞模型。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.