U.S. EPA, Office of Research and Development, Research Triangle Park, NC 27711, United States.
Sci Total Environ. 2013 Mar 15;448:107-19. doi: 10.1016/j.scitotenv.2012.12.046. Epub 2013 Jan 30.
Intra-storm variability and soluble fractionation was explored for summer-time rain events in Steubenville, Ohio to evaluate the physical processes controlling mercury (Hg) in wet deposition in this industrialized region. Comprehensive precipitation sample collection was conducted from July through September 2006 using three different methods to evaluate both soluble and insoluble fractions as well as scavenging and washout properties of Hg and a suite of trace elements. Real-time filtration of event total precipitation revealed that 61±17% (mean±standard deviation) of Hg in wet deposition was in a soluble form. Comparison of total and dissolved element concentrations (solubility fractionation) showed the following order of decreasing solubility: S>Na>Se>Ca>Mg>Hg>As>Mn>V>Cr>Fe>La≈Ce ranging from 95% (S) to 4% (Ce). To examine removal mechanisms occurring during the course of a precipitation event, discrete, sequential sub-event precipitation samples were collected. Results indicated that Hg had lower "scavenging coefficients" (the rate of Hg concentration decrease throughout the events) than the majority of elements analyzed, indicating that either (i) Hg is incorporated into rain via gas phase inclusion or particulate nucleation within cloud, or (ii) Hg is available in the boundary layer for scavenging, even in the latter stages of precipitation. The Hg scavenging coefficient (-0.39) was low compared to S (-0.73), a co-pollutant of Hg. When compared to an upwind, regionally representative site, the scavenging coefficient of Hg for the locally influenced precipitation was 25% lower. This observation suggests that a continuous feed of soluble Hg was the reason for the low scavenging coefficient. Overall, this investigation of Hg wet deposition in Steubenville indicates that the physical and chemical properties of Hg emissions are driving the elevated deposition rates observed near point sources.
本研究旨在探索俄亥俄州斯图本维尔市夏季降雨事件的风暴内变异性和可溶解分馏作用，以评估控制该工业化地区湿沉降汞（Hg）的物理过程。2006 年 7 月至 9 月期间，采用三种不同方法进行了综合降水样本采集，以评估可溶性和不可溶性分数以及 Hg 和一系列微量元素的清除和冲刷特性。事件总降水的实时过滤表明，湿沉降中 61±17%（均值±标准差）的 Hg 呈可溶解形式。总元素和溶解元素浓度（溶解度分馏）的比较表明，Hg 的溶解度从高到低的顺序为：S>Na>Se>Ca>Mg>Hg>As>Mn>V>Cr>Fe>La≈Ce，范围从 95%（S）到 4%（Ce）。为了研究降水事件过程中发生的去除机制，采集了离散的、顺序的亚事件降水样本。结果表明，Hg 的“清除系数”（整个事件过程中 Hg 浓度的下降率）低于分析的大多数元素，这表明 Hg 要么（i）通过气相包含或云内颗粒物成核而包含在雨中，要么（ii）在边界层中可用于清除，即使在降水的后期阶段也是如此。Hg 的清除系数（-0.39）与 S（-0.73）相比较低，S 是 Hg 的共污染物。与上风方向、具有区域代表性的站点相比，受局地影响的降水的 Hg 清除系数低 25%。这一观察结果表明，可溶性 Hg 的连续供应是清除系数低的原因。总的来说，本研究表明，Hg 排放的物理和化学性质是造成点源附近观察到的高沉积率的原因。
