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DRIFT dispersion model predictions for the Jack Rabbit II model inter-comparison exercise
Atmospheric Environment ( IF 5 ) Pub Date : 2021-01-01 , DOI: 10.1016/j.atmosenv.2020.117717
Simon Gant , Graham Tickle , Adrian Kelsey , Harvey Tucker

Abstract In 2015, 2016, the US Army conducted nine large-scale chlorine releases at the Dugway Proving Ground in Utah, known as the Jack Rabbit II trials. The purpose of these experiments was to improve our understanding of pressure-liquefied chlorine releases and atmospheric dispersion, and to provide useful practical knowledge for emergency responders. Data from three of the Jack Rabbit II trials (Trials 1, 6 and 7) were subsequently selected for an international model inter-comparison exercise, which included modelling contributions from the US, UK, Canada, France, Germany, Sweden, Finland and the European Commission. This paper provides details of one of the UK contributions to that exercise, using the DRIFT integral dispersion model. Participants in the exercise were given a set of prescribed model input conditions. The methodology used in DRIFT to model these conditions is described here, which consisted of three runs: a baseline case and two sensitivity tests that examined the effect of variations in the modelled wind-speed profile and the dry deposition rate. A brief review is also provided of the experimental data used for the model inter-comparison exercise. Gas concentrations were measured in the Jack Rabbit II trials using an extensive array of gas sensors arranged on arcs downwind from the release point. Four types of sensors were used, which each had calibration and/or saturation limits. In some of the trials, sensors that recorded the highest concentrations on an arc were saturated with gas and under-recorded the actual concentrations. In other cases, especially near the source, there were only a few sensors on an arc and therefore it is uncertain whether the plume maximum concentrations were recorded. Results from DRIFT are compared to the Jack Rabbit II data in two ways. Firstly, against the full dataset of maximum arc-wise concentrations, and secondly against the subset of measurements that were unaffected by saturation issues or there being a sparse sensor array. In the first case, DRIFT gives higher concentrations than were measured on average, noting that some measurements probably under-recorded the concentration owing to the previously mentioned sensor saturation issues. In the second case, using the more reliable dataset, the statistical performance of DRIFT falls within commonly-used dense-gas model acceptance criteria. Sensitivity tests on the wind speed profile and dry deposition rate had an effect on the DRIFT predictions in Trial 1, but little impact in Trials 6 and 7. This behaviour is likely to be due to the changing meteorology during Trial 1, and the lower wind speed and smaller chlorine mass released in that trial. Remaining knowledge gaps and possible future directions for research are discussed. These include further work on dry deposition, modelling of the other Jack Rabbit II trials (potentially using source models as well as prescribed common source conditions), and comparisons of predicted and measured toxic load, calculated from the time-varying concentrations.

中文翻译:

Jack Rabbit II 模型比对练习的 DRIFT 离散模型预测

摘要 2015年、2016年,美国陆军在犹他州达格威试验场进行了9次大规模氯气释放试验,称为杰克兔II型试验。这些实验的目的是提高我们对压力液化氯释放和大气扩散的理解,并为应急响应人员提供有用的实践知识。随后选择了来自 Jack Rabbit II 试验(试验 1、6 和 7)中的三项数据进行国际模型比对练习,其中包括来自美国、英国、加拿大、法国、德国、瑞典、芬兰和欧盟委员会。本文使用 DRIFT 积分色散模型提供了英国对该练习的一项贡献的详细信息。练习的参与者获得了一组规定的模型输入条件。此处描述了 DRIFT 中用于模拟这些条件的方法,该方法由三个运行组成:一个基线案例和两个敏感性测试,用于检查模拟风速剖面和干沉降率变化的影响。还简要回顾了用于模型比对练习的实验数据。在 Jack Rabbit II 试验中,使用大量气体传感器测量气体浓度,这些传感器布置在释放点顺风方向的弧线上。使用了四种类型的传感器,每一种都有校准和/或饱和限制。在一些试验中,记录电弧最高浓度的传感器被气体饱和,而实际浓度记录不足。在其他情况下,尤其是在源头附近,电弧上只有几个传感器,因此不确定是否记录了羽流最大浓度。DRIFT 的结果以两种方式与 Jack Rabbit II 数据进行比较。首先,针对最大弧向浓度的完整数据集,其次针对不受饱和问题影响或存在稀疏传感器阵列的测量子集。在第一种情况下,DRIFT 给出的浓度高于平均测量值,并指出由于前面提到的传感器饱和问题,一些测量值可能记录不足。在第二种情况下,使用更可靠的数据集,DRIFT 的统计性能符合常用的稠密气体模型验收标准。风速剖面和干沉降率的敏感性测试对试验 1 中的 DRIFT 预测有影响,但在试验 6 和 7 中影响不大。 这种行为可能是由于试验 1 期间气象变化,以及较低的风该试验中释放的氯质量更小。讨论了剩余的知识差距和未来可能的研究方向。其中包括干沉积的进一步工作、其他 Jack Rabbit II 试验的建模(可能使用源模型以及规定的常见源条件),以及根据时变浓度计算预测和测量的毒性负荷的比较。并且在该试验中释放的较低风速和较小氯质量。讨论了剩余的知识差距和未来可能的研究方向。其中包括干沉积的进一步工作、其他 Jack Rabbit II 试验的建模(可能使用源模型以及规定的常见源条件),以及根据时变浓度计算预测和测量的毒性负荷的比较。并且在该试验中释放的较低风速和较小氯质量。讨论了剩余的知识差距和未来可能的研究方向。其中包括干沉积的进一步工作、其他 Jack Rabbit II 试验的建模(可能使用源模型以及规定的常见源条件),以及根据时变浓度计算预测和测量的毒性负荷的比较。
更新日期:2021-01-01
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