Intensive traffic emissions have caused many environmental problems and have a negative effect on public health. With the aim of mitigating these problems, it is essential to figure out how the flow structure affects the pollutant dispersion within the urban canopy. Most previous studies focus on the canopy vortex caused by top entrainment, but few previous studies are aware of the importance of lateral entrainment. By conducting computational fluid dynamic (CFD) simulations validated by wind tunnel data, we investigate the effects of lateral entrainment on pollutant dispersion inside a street canyon. Eight three-dimensional street canyons with various building heights and street lengths are considered. Besides, three optimal design strategies are proposed to improve the air quality by enhancing the lateral entrainment. The results of this analysis demonstrate that lateral entrainment could conditionally reduce the pollutant concentration of low-rise canyons. This reduction, which is affected by lateral entrainment, is confined in a range of approximately 2.5 times the street width from the street ends. In contrast, the lateral entrainment causes a more pronounced reduction in the pollutant concentrations of the high-rise canyons. Besides, all three strategies can considerably facilitate the lateral entrainment, leading to a significant reduction in the cross-section pollutant concentrations (by up to 76%) and therefore a significant reduction in the personal intake fraction P_IF of the residents (by up to 81%).

密集的交通排放已引起许多环境问题，并对公共卫生产生负面影响。为了减轻这些问题，必须弄清楚流量结构如何影响城市雨棚内的污染物扩散。先前的大多数研究都集中在由顶部夹带引起的冠层涡旋上，但是很少有先前的研究意识到侧向夹带的重要性。通过进行风洞数据验证的计算流体动力学（CFD）模拟，我们研究了横向夹带对街道峡谷内污染物扩散的影响。考虑了八个具有不同建筑物高度和街道长度的三维街道峡谷。此外，提出了三种优化设计策略，通过增强侧向夹带来改善空气质量。分析结果表明，横向夹带可以有条件地降低低矮峡谷的污染物浓度。受侧向夹带影响的这种减小被限制在距街道末端的街道宽度的大约2.5倍的范围内。相反，横向夹带引起高层峡谷污染物浓度的更明显降低。此外，这三种策略都可以极大地促进侧向夹带，从而显着降低横截面污染物浓度（最多降低76％），从而显着降低个人摄入量 被限制在距离街道末端约2.5倍的街道宽度范围内。相反，横向夹带引起高层峡谷污染物浓度的更明显降低。此外，这三种策略都可以极大地促进侧向夹带，从而显着降低横截面污染物浓度（最多降低76％），从而显着降低个人摄入量 被限制在距离街道末端约2.5倍的街道宽度范围内。相反，横向夹带引起高层峡谷污染物浓度的更明显降低。此外，这三种策略都可以极大地促进侧向夹带，从而显着降低横截面污染物浓度（最多降低76％），从而显着降低个人摄入量居民的P_IF（最高81％）。