Urbanization modifies the bottom of the atmospheric boundary layer (ABL) leading to elevated air pollutant concentrations. Over 50% of the world population lives in cities nowadays [1]. Urban air quality is thus a problem of major concern. The meteorological process in the urban canopy layer (UCL) exhibits a distinct, neighborhood-scale climate full of wakes and recirculations. A street canyon is the generic unit commonly used in urban pollutant transport studies [2]. In urban meteorology, the flows over idealized two-dimensional (2D) street canyons are classified into three characteristic flow regimes, viz., isolated roughness, wake interference, and skimming flow, as functions of the building-height-to-street-width ratio h/b [3]. Similarly, in fluid mechanics, flow over a rough wall with 2D ribs is broadly divided into d-type or k-type, depending on the separation between the ribs [4].
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机译：城市化改变了大气边界层（ABL）的底部，导致空气污染物浓度升高。现在世界上有超过50％的人口生活在城市[1]。因此，城市空气质量是主要关注的问题。城市冠层层（UCL）的气象过程呈现出鲜明的邻近气候，充满了唤醒和再循环。街道峡谷是城市污染物运输研究中常用的通用单元[2]。在城市气象学中，在理想化的二维（2D）街道峡谷上的流量分为三个特征流动制度，偏离粗糙度，唤醒干扰和掠过流动，作为建筑高度到街道宽度的功能比率h / b [3]。类似地，在流体力学中，在具有2D肋的粗糙壁上流动，大致分为D型或K型，这取决于肋条之间的分离[4]。
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