Gaseous elemental mercury (GEM), the primary form of mercury (Hg) in the atmosphere, can undergo bidirectional exchange with the Earth's surface, with uptake in growing vegetation constituting the dominant atmospheric deposition process. Whereas direction and magnitude of this exchange can be determined using micrometeorological and chamber techniques, these approaches are complex, costly and labor-intensive, and often only yield fluxes over relatively short time-scales at few sites. We demonstrate that an inexpensive and easy-to-use passive air sampler can identify and quantify vertical GEM concentration gradients on scales ranging from centimeters to tens of meters over long time periods (up to 1.5 years) and with coarse temporal resolution (monthly to seasonally). Samplers were deployed above clean and contaminated soil and through a deciduous forest canopy at two sites in Southern Ontario. Significant and seasonally variable gradients of GEM concentrations, both increasing and decreasing with height above ground, were observed and can be explained through the influence of factors such as soil contamination, canopy growth, temperature, solar irradiance, and snow cover. At a minimum, the sampler can identify the GEM flux direction, but, when combined with the Modified Bowen Ratio method, can also be used to estimate the evaporative GEM flux from mercury-contaminated soil. We further demonstrate the application of the approach to contaminated site assessment, using a field in Brescia, Italy, known to contain elevated levels of Hg in soil. By allowing for cost-effective measurements at multiple sites and over extended time periods, passive sampling complements existing techniques for studying atmosphere-surface exchange of GEM.

中文翻译：

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使用被动空气采样器量化森林和土壤以上垂直气态元素汞浓度梯度

气态元素汞 (GEM) 是大气中汞 (Hg) 的主要形式，可以与地球表面进行双向交换，生长中的植被吸收构成主要的大气沉积过程。虽然这种交换的方向和幅度可以使用微气象学和腔室技术来确定，但这些方法复杂、昂贵且劳动密集型，并且通常只能在少数地点在相对较短的时间范围内产生通量。我们证明了一种廉价且易于使用的被动式空气采样器可以识别和量化从厘米到数十米的长期 GEM 浓度梯度在很长一段时间内（长达 1.5 年）和粗略的时间分辨率（每月到季节性） ）。采样器被部署在清洁和受污染的土壤上方，并穿过安大略省南部两个地点的落叶林冠层。观察到 GEM 浓度的显着和季节性变化梯度，随着离地高度的增加和减少，可以通过土壤污染、冠层生长、温度、太阳辐照度和积雪等因素的影响来解释。采样器至少可以识别 GEM 通量方向，但是，当与修正鲍温比法结合使用时，还可用于估计来自汞污染土壤的蒸发 GEM 通量。我们进一步展示了该方法在污染场地评估中的应用，使用意大利布雷西亚的一个已知土壤中汞含量升高的田地。