Volcanic mercury: local deposition or global dispersion?

汞是一种有毒金属，通过人类活动（例如煤炭燃烧）和自然过程释放到我们的环境中。一旦进入海洋或其他水环境，它就会转化为有毒形式，然后进入食物链，并对动物的中枢神经系统造成损害。汞污染是一个严重的人类健康问题，因此了解其不同的全球来源非常重要。最近的研究表明，与全球范围内的其他来源相比，持续脱气的火山是大气中汞的重要来源。最近对活火山口的测量也表明，火山汞主要以气体形式排放。这种气体的溶解度不太高（例如，在雨水中），因此无法非常有效地从大气中去除，这意味着它可以从其来源输送到很远的距离，从而使火山汞成为全球环境危害。然而，在排放点顺风的火山羽流中也观察到了活性溴化合物。在极地地区和死海，活性溴化合物被认为会导致气态汞（由于来源遥远，在这些环境中含量较低）迅速转化为更易溶解的形式，然后迅速沉积到当地环境中。如果火山羽流中发生类似的化学反应，那么它们将对当地生态系统造成重大的汞危害，因为这种化学反应不仅会导致来自遥远来源的低含量大气汞快速沉积，而且还会导致火山羽流中存在的汞含量显着增加。我们想要了解汞在火山羽流中的行为以及局部沉积和全球扩散之间的平衡。我们将测量尼加拉瓜马萨亚火山火山口边缘的持久非爆炸性火山羽流中发现的汞含量和类型，以及火山顺风处已知羽流定期落地的两个位置。我们还将测量这些地点的活性溴水平和火山羽流的其他成分，并将建立一个采样器网络来测量从火山到当地顺风环境的汞沉积通量。这些测量将使我们能够检验我们的假设，即在火山羽流中，气态汞将迅速转化为更具反应性的形式，然后沉积到当地环境中。然后，这些测量结果将用于调整火山羽流中发生的大气化学的现有计算机模型，以包括汞化学。这将使我们进一步了解火山汞处理，并了解活火山排放的汞的去向，特别是了解火山汞排放是否会造成局部或全球危害。

Mercury is a toxic metal released to our environment through mankind's activities (e.g., coal burning) and natural processes. Once it gets into the sea or other aqueous environments it can be transformed into toxic forms, which can then get into the food chain and can cause damage to the central nervous systems of animals. Mercury pollution is a grave human health concern and so it is important to understand its different global sources. Recent work has shown that continuously degassing volcanoes represent a significant source of mercury to the atmosphere compared to other sources on the global scale. Recent measurements at active volcanic craters have also shown that volcanic mercury is primarily emitted as a gas. This gas is not very soluble (e.g., in rainwater) and so would not be very efficiently removed from the atmosphere meaning that it could be transported very long distances from its source making volcanic mercury a global environmental hazard. However reactive bromine compounds have also been observed in volcanic plumes downwind from the point of emission. In the Polar Regions and at the Dead Sea reactive bromine compounds are thought to lead to the rapid transformation of gaseous mercury (present in these environments at low levels due to remote sources) into more soluble form that are then rapidly deposited to the local environment. If similar chemistry occurs in volcanic plumes then they will represent a significant mercury hazard to local ecosystems as this chemistry would not only lead to the rapid deposition of low levels of atmospheric mercury from remote sources but also the very significantly enhanced levels present in volcanic plumes. We want to understand the behaviour of mercury in volcanic plumes and the balance between local deposition and global dispersion. We will make measurements of the levels and types of mercury found in the persistent non-explosive volcanic plume from Masaya volcano in Nicaragua at the crater rim and at two locations downwind of the volcano where the plume is known to ground regularly. We will also measure reactive bromine levels and other constituents of the volcanic plume at these locations and will put out a network of samplers to measure the deposition flux of mercury to the local downwind environment from the volcano. These measurements will allow us to test our hypothesis that in volcanic plumes, gaseous mercury will be rapidly transformed to more reactive forms that are then deposited to the local environment. These measurements will then be used to adapt existing computer models of the atmospheric chemistry occurring in volcanic plumes to include mercury chemistry. This will allow us to further our understanding of volcanic mercury processing as well as to build up a picture of the fate of the mercury emitted from active volcanoes and specifically to understand whether volcanic mercury emissions pose a local or global hazard.