In this study we introduce a novel extension of an existing Lagrangian particle dispersion model for application over urban areas by explicitly taking into account the urban canopy layer. As commonly done, the original model uses the zero-plane displacement as a lower boundary condition, while the extension reaches to the ground. To achieve this, spatially-averaged parametrizations of flow and turbulence characteristics are created by fitting functions to observational and numerical data. The extended model is verified with respect to basic model assumptions (well-mixed condition) and its behaviour is investigated for unstable/neutral/stable atmospheric stabilities. A sensitivity study shows that the newly introduced model parameters characterizing the canopy turbulence impact the model output less than previously existing model parameters. Comparing concentration predictions to the Basel Urban Boundary Layer Experiment—where concentrations were measured near roof level—shows that the modified model performs slightly better than the original model. More importantly, the extended model can also be used to explicitly treat surface sources (traffic) and assess concentrations within the urban canopy and near the surface (pedestrian level). The small improvement with respect to roof level concentrations suggests that the parametrized canopy profiles for flow and turbulence characteristics realistically represent the dispersion environment on average.

在这项研究中，我们通过明确考虑城市冠层，引入了现有拉格朗日粒子分散模型的新扩展，以应用于城市地区。正如通常所做的那样，原始模型使用零平面位移作为下边界条件，而延伸到达地面。为了实现这一点，通过将函数拟合到观测和数值数据来创建流动和湍流特性的空间平均参数化。扩展模型在基本模型假设（充分混合条件）方面进行了验证，并针对不稳定/中性/稳定大气稳定性研究了其行为。敏感性研究表明，新引入的表征冠层湍流的模型参数对模型输出的影响小于以前存在的模型参数。将浓度预测与巴塞尔城市边界层实验（在屋顶水平附近测量浓度）进行比较表明，修改后的模型的性能略好于原始模型。更重要的是，扩展模型还可用于明确处理地表源（交通）并评估城市树冠内和地表附近（行人水平）的浓度。屋顶水平浓度的微小改进表明，流动和湍流特性的参数化冠层剖面实际上代表了平均分散环境。扩展模型还可用于明确处理地表源（交通）并评估城市树冠内和地表附近（行人水平）的浓度。屋顶水平浓度的微小改进表明，流动和湍流特性的参数化冠层剖面实际上代表了平均分散环境。扩展模型还可用于明确处理地表源（交通）并评估城市树冠内和地表附近（行人水平）的浓度。屋顶水平浓度的微小改进表明，流动和湍流特性的参数化冠层剖面实际上代表了平均分散环境。