Investigating methane emissions from geologic microseepage in Western New York State, United States
Investigating methane emissions from geologic microseepage in Western New York State, United States
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DOI：
10.1525/elementa.2020.00066
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发表时间：
2021-01
期刊：
影响因子：
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通讯作者：
R. Kazemi;W. Schlageter;B. Hmiel;T. Weber;L. Murray;V. Petrenko
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文献类型：
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作者：
R. Kazemi;W. Schlageter;B. Hmiel;T. Weber;L. Murray;V. Petrenko
甲烷是一种强大的温室气体，也是大气化学的关键参与者。全球大气甲烷预算仍然存在重要的不确定性，其中自然地质排放是特别不确定的术语之一。在最近的自下而上的研究中，地质排放估计占全球预算的 10%（每年 40-60 太克甲烷，Tg CH4 yr–1）。相比之下，从冰芯中提取的工业化前空气中甲烷 14C 的自上而下的限制表明，地质甲烷来源大约低一个数量级。最近的自下而上的清单提出，微渗漏（通过大面积土壤扩散低水平的甲烷通量）是地质甲烷通量的最大单一组成部分。在这项研究中，我们提出了阿巴拉契亚盆地（纽约州西部）甲烷微渗漏的新测量结果，并将其与其他地区之前的微渗漏测量值以及最新自下而上清单的预测值进行了比较。我们的结果显示，微渗流值比大多数先前的数据集要低，并表明该区域的正微渗流通量并不像之前假设的那样广泛。对我们结果的统计分析表明，自下而上的清单很可能高估了该区域的平均微渗流通量，尽管我们的测量更有可能低估了真实的平均通量。然而，这是来自单个区域的小数据集，因此不能用于评估整个微渗漏排放清单的有效性。相反，结果表明需要更广泛的直接地质排放测量网络来支持改进的自下而上的清单。
Methane is a powerful greenhouse gas and a key player in atmospheric chemistry. Important uncertainties remain in the global atmospheric methane budget, with natural geologic emissions being one of the particularly uncertain terms. In recent bottom-up studies, geologic emissions have been estimated to comprise up to 10% of the global budget (40–60 Teragrams of methane per year, Tg CH4 yr–1). In contrast, top-down constraints from 14C of methane in preindustrial air extracted from ice cores indicate that the geologic methane source is approximately an order of magnitude lower. Recent bottom-up inventories propose microseepage (diffuse low-level flux of methane through soils over large areas) as the largest single component of the geologic methane flux. In this study, we present new measurements of methane microseepage from the Appalachian Basin (Western New York State) and compare these with prior microseepage measurements from other regions and with predicted values from the most recent bottom-up inventory. Our results show lower microseepage values than most prior data sets and indicate that positive microseepage fluxes in this region are not as widespread as previously assumed. A statistical analysis of our results indicates that mean microseepage flux in this region has very likely been overestimated by the bottom-up inventory, even though our measurements more likely than not underestimate the true mean flux. However, this is a small data set from a single region and as such cannot be used to evaluate the validity of the microseepage emissions inventory as a whole. Instead, the results demonstrate the need for a more extensive network of direct geologic emission measurements in support of improved bottom-up inventories.