The accumulated particulate matter concentration at a given vertical column due to traffic sources in urban area has many important consequences. This task, however, imposes a major challenge, since the problem of realistic pollutant dispersion in an urban environment is a very demanding task, both theoretically and computationally. This is mainly due to the highly inhomogeneous three dimensional turbulent flow regime in the urban canopy roughness sublayer, which is far from “local equilibrium” between shear production and dissipation. We present here a mass-consistent urban Lagrangian stochastic model for pollutants dispersion, where the flow field is modeled using a hybrid approach by which we model the surface layer based on the typical turbulent scales, both of the canopy and in the surface layer inertial sub-layer. In particular it relies on representing the canopy aerodynamically as a porous medium by spatial averaging the equations of motion, with the assumption that the canopy is laterally uniform on a scale much larger than the buildings but smaller than the urban block/neighbourhood, i.e., at the sub-urban-block scale. Choosing the spatial representative averaging volume allows the averaged variables to reflect the characteristic vertical heterogeneity of the canopy but to smooth out smaller scale spatial fluctuations caused as air flows in between the buildings. This modeling approach serves as the base for a realistic and efficient methodology for the calculation of the accumulated concentration from multiple traffic sources for any vertical column in the urban area. The existence of multiple traffic sources impose further difficulty since the computational effort required is very demanding for practical uses. Therefore, footprint analysis screening was introduced to identify the relevant part of the urban area which contributes to the chosen column. All the traffic sources in this footprint area where merged into several areal sources, further used for the evaluation of the concentration profile. This methodology was implemented for four cases in the Tel Aviv metropolitan area based on several selected summer climatological scenarios. We present different typical behaviors, demonstrating combination of source structure, urban morphology, flow characteristics, and the resultant dispersion pattern in each case.

中文翻译：

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模拟交通颗粒物浓度场的城市拉格朗日随机色散模型

由于城市地区的交通来源，给定垂直柱上累积的颗粒物浓度具有许多重要的后果。然而，由于从理论上和计算上来说，城市环境中污染物的实际扩散问题都是一项非常艰巨的任务，因此该任务提出了一项重大挑战。这主要是由于城市冠层粗糙度次层中高度不均匀的三维湍流状态，与剪切产生和消散之间的“局部平衡”相去甚远。我们在这里提出了一种用于污染物扩散的质量一致的城市拉格朗日随机模型，其中使用混合方法对流场进行建模，通过该方法，我们基于典型的湍流尺度对表层进行建模，包括机盖和表层惯性子-层。特别地，它假设通过对运动方程进行空间平均，将冠层在空气动力学上表示为多孔介质，并假设冠层的横向均匀性要比建筑物大得多，但要小于城市街区/街区，即在郊区街区规模。选择空间代表性的平均体积可以使平均变量反映树冠的特征性垂直异质性，但可以消除因建筑物之间的空气流动而引起的较小规模的空间波动。这种建模方法为现实高效的方法提供了基础，该方法可用于计算市区内任何垂直立柱来自多个交通源的累积浓度。多个交通源的存在进一步增加了难度，因为对于实际应用而言，所需的计算量非常高。因此，引入了足迹分析筛选以识别有助于选择列的市区的相关部分。该足迹区域中的所有交通源都合并为多个面源，进一步用于评估浓度曲线。根据几种选定的夏季气候情景，在特拉维夫市辖区的4个案例中采用了这种方法。我们展示了不同的典型行为，展示了每种情况下源结构，城市形态，流量特征以及由此产生的分散模式的组合。引入了足迹分析筛选，以识别有助于选择列的市区的相关部分。该足迹区域中的所有交通源都合并为多个面源，进一步用于评估浓度曲线。根据几种选定的夏季气候情景，在特拉维夫市辖区的4个案例中采用了这种方法。我们展示了不同的典型行为，展示了每种情况下源结构，城市形态，流量特征以及由此产生的分散模式的组合。引入了足迹分析筛选，以识别有助于选择列的市区的相关部分。该足迹区域中的所有交通源都合并为多个面源，进一步用于评估浓度曲线。根据几种选定的夏季气候情景，在特拉维夫市辖区的4个案例中采用了这种方法。我们展示了不同的典型行为，展示了每种情况下源结构，城市形态，流量特征以及由此产生的分散模式的组合。根据几种选定的夏季气候情景，在特拉维夫市辖区的4个案例中采用了这种方法。我们展示了不同的典型行为，展示了每种情况下源结构，城市形态，流量特征以及由此产生的分散模式的组合。根据几种选定的夏季气候情景，在特拉维夫市辖区的4个案例中采用了这种方法。我们展示了不同的典型行为，展示了每种情况下源结构，城市形态，流量特征以及由此产生的分散模式的组合。