Following the release of a harmful substance within an urban environment, buildings and street canyons create complex flow regimes that affect dispersion and localized effluent concentrations. While some fast-response dispersion models can capture the effects caused by individual buildings, further research is required to refine urban characterizations such as plume channeling and spreading, and initial dispersion, especially within the presence of a nonhomogeneous array of structures. Field, laboratory, and modeling experiments that simulate urban or industrial releases are critical in advancing current dispersion models. This project leverages the configuration of buildings used in a full-scale, mock urban field study to examine the concentrations of a neutrally buoyant tracer in a series of wind tunnel and Embedded Large Eddy Simulation (ELES) experiments. The behavior, propagation, and magnitude of the plumes were examined and compared to identify microscale effects.

After demonstrating excellent quantitative and qualitative comparisons between the wind tunnel and ELES via lateral and vertical concentration profiles, we show that a nonlinear least squares fit of the Gaussian plume equation well represents these profiles, even within the array of buildings and network of street canyons. The initial plume dispersion depended strongly on the structures immediately adjacent to the release, and consequently, the near-surface plume spread very rapidly in the first few street canyons downwind of the source. The ELES modeling showed that under slightly oblique incoming wind directions of 5° and 15°, an additional 5° and 14° off-axis channeling of the plume occurred at ground level, respectively. This indicates how building structures can cause considerable plume drift from the otherwise expected centerline axis, especially with greater wind obliquity. Additionally, AERMOD was used to represent the class of fast-running, Gaussian dispersion models to inform where these types of models may be usefully applied within urban areas or groups of buildings. Using an urban wind speed profile and other parameters that may be locally available after a release, AERMOD was shown to qualitatively represent the ground-level plume while somewhat underestimating peak concentrations. It also overestimated the lateral plume spread and was challenged in the very near-field to the source. Adding a turbulence profile from the ELES data into AERMOD's meteorological input improved model estimates of lateral plume spread and centerline concentrations, although peak concentration values were still underestimated in the far field. Finally, we offer some observations and suggestions for Gaussian dispersion modeling based on this mock urban modeling exercise.

随着城市环境中有害物质的释放，建筑物和街道峡谷会产生复杂的流态，影响扩散和局部污水浓度。虽然一些快速响应的扩散模型可以捕捉单个建筑物造成的影响，但需要进一步研究来完善城市特征，例如羽流通道和扩散以及初始扩散，特别是在存在非均匀结构阵列的情况下。模拟城市或工业排放的现场、实验室和建模实验对于推进当前的扩散模型至关重要。该项目充分利用建筑物的配置，模拟城市实地研究，以检查一系列风洞和嵌入式大涡模拟 (ELES) 实验中中性浮力示踪剂的浓度。对羽流的行为、传播和大小进行了检查和比较，以确定微尺度效应。

在通过横向和垂直浓度剖面展示了风洞和 ELES 之间出色的定量和定性比较之后，我们表明高斯羽流方程的非线性最小二乘拟合很好地代表了这些剖面，即使在建筑物阵列和街道峡谷网络中也是如此。最初的羽流扩散强烈依赖于紧邻排放的结构，因此，近地表羽流在源头顺风的前几个街道峡谷中迅速扩散。ELES 模型显示，在 5° 和 15° 的略微倾斜的来风方向下，在地面上分别发生了额外的 5° 和 14° 的烟羽离轴通道。这表明建筑结构如何导致从原本预期的中心线轴线产生相当大的羽流漂移，尤其是在风倾角较大的情况下。此外，AERMOD 用于表示快速运行的高斯色散模型类别，以告知这些类型的模型可以在城市区域或建筑物群中有效应用的位置。使用城市风速剖面和其他可能在释放后当地可用的参数，AERMOD 被证明定性地代表了地面羽流，但在某种程度上低估了峰值浓度。它还高估了横向羽流扩散，并在非常靠近源头的地方受到挑战。将 ELES 数据中的湍流剖面添加到 AERMOD 的气象输入中改进了对横向羽流扩散和中心线浓度的模型估计，尽管远场的峰值浓度值仍然被低估。最后，