Chemistry, transport, emission, and shading effects on NO2 and Ox distributions within urban canyons.
Chemistry, transport, emission, and shading effects on NO2 and Ox distributions within urban canyons.
复制标题
DOI：
10.1016/j.envpol.2022.120347
复制
发表时间：
2022-10
影响因子：
8.9
通讯作者：
Yuqing Dai;Xiaoming Cai;Jian Zhong;A. Mazzeo;A. MacKenzie
中科院分区：
文献类型：
--
作者：
Yuqing Dai;Xiaoming Cai;Jian Zhong;A. Mazzeo;A. MacKenzie
预测街道峡谷内 NO2 和总氧化剂 (Ox=NO2+O3) 的能力对于评估旨在提高城市热点地区人类福祉的空气质量法规至关重要。然而，这种评估需要街道尺度的众多过程的耦合，例如车辆排放以及紧密耦合的运输和光化学过程。尤其是光化学，经常被忽视、严重简化或参数化。在这项研究中，MBM-FleX——一种基于过程的街道峡谷模型，可以通过紧密耦合的物理（传输和混合）和化学过程快速计算各种排放剖面和阳光照射条件，并且不会损失足够的空间分辨率——用于模拟城市峡谷内活性物质的遮蔽效应。在预先生成的大涡流模拟的驱动下，MBM-FleX 结果表明，对挥发性有机化合物 (VOC) 自由基的遮蔽效应会显着影响简单的 NOx-O3 化学无法捕获的奇数氧物质的相互转化，例如，通过限制氢过氧自由基的形成来还原 NO2。与之前在更简单的模型系统中的结果一致，VOC自由基化学的包含并没有明显改变常规峡谷中NO2对遮蔽强度的敏感性，但是当空气停留时间增加时，在深峡谷中发现NO2和遮蔽强度之间存在非线性关系。当太阳入射同时穿过街道峡谷中的多个涡流时，VOC 化学成分和阴影可能会显着影响模型结果，从而影响城市规划策略和个人暴露评估的制定。
The capacity to predict NO2and the total oxidant (Ox= NO2+ O3) within street canyons is critical for the assessment of air quality regulations aimed at enhancing human wellbeing in urban hotspots. However, such assessment requires the coupling of numerous processes at the street-scale, such as vehicular emissions and tightly coupled transport and photochemical processes. Photochemistry, in particular, is often ignored, heavily simplified, or parameterized. In this study, MBM-FleX — a process-based street canyon model that allows fast computation of various emission profiles and sun-lit conditions with tightly coupled physical (transport and mixing) and chemical processes and without loss of sufficient spatial resolution — was used to simulate shading effects on reactive species within urban canyons. Driven by pre-generated large-eddy simulation of flow, MBM-FleX results show that shading effects on volatile organic compound (VOC) free-radicals significantly affect the interconversion of odd-oxygen species that cannot be captured by the simple NOx-O3chemistry, for example, reducing NO2by limiting the formation of hydroperoxyl radicals. Consistent with previous results in simpler model systems, the inclusion of VOC free-radical chemistry did not appreciably alter the sensitivity of NO2to shading intensity in regular canyons, but a non-linear relationship between NO2and shading intensity is found in deep canyons when the air residence time grew. When solar incidence simultaneously passes through multiple vortices in street canyons, VOC chemistry and shade may considerably influence model results, which may therefore affect the development of urban planning strategies and personal exposure evaluation.