School of Atmospheric Sciences, Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies, Sun Yat-sen University, Guangzhou, PR China.
School of Atmospheric Sciences, Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies, Sun Yat-sen University, Guangzhou, PR China; Key Laboratory of Tropical Atmosphere-Ocean System (Sun Yat-sen University), Ministry of Education, 519000 Zhuhai, PR China.
Sci Total Environ. 2021 Mar 10;759:143527. doi: 10.1016/j.scitotenv.2020.143527. Epub 2020 Nov 16.
This study incorporates solar radiation model and NO-O photochemistry into computational fluid dynamics (CFD) simulations with the standard k-ε model to quantify the integrated impacts of turbulent mixing, solar heating and chemical processes on vehicular passive (CO) and reactive (NO, O) pollutant dispersion within two-dimensional (2D) street canyons. Various street aspect ratios (H/W = 1, 3, 5) and solar-radiative scenarios (LST 0900, 1200, 1500) are considered. The initial source ratio of NO to NO is 1:10 and the background O concentration is 100 ppb (mole fraction). The reference Reynolds numbers are ~10-10 and Froude number ranges from 0.23 to 1.14. Personal intake fraction (P_IF) and its spatially-averaged values at the leeward-side (⟨P_IF⟩), windward-side (⟨P_IF⟩) and both street sides (⟨P_IF⟩) are adopted to evaluate pollutant exposure in near-road buildings. As H/W = 1 and 3, the clockwise single vortex is formed under neutral condition. Leeward/ground solar heating at LST 0900/1200 slightly enhance such vortex and reduce ⟨P_IF⟩. However, as H/W = 3, the single dominant vortex is separated into two counter-rotating vortices by windward solar heating at LST 1500, thus this ⟨P_IF⟩ is significantly larger than the neutral case. As H/W = 5, the lower-level secondary anticlockwise vortex appears under neutral condition inducing much weaker wind and extremely higher pedestrian-level concentration. This two-main-vortex structure is destroyed by leeward/ground heating into single-main-vortex pattern, but dissociates into three counter-rotating vortices by windward heating. These three radiative scenarios raise pedestrian-level velocity in neutral case by about two orders, and reduce overall ⟨P_IF⟩ by two times to one order. For all cases, NO exposure is generally about 40%-380% larger than passive CO exposure, which indicates the conversion of NO into NO by depleting O is dominant in present NO-O titration interactions. Finally, solar heating only raises air temperature by up to 2-3 K and influences chemical rate slightly, thus this impact on reactive pollutant dispersion is less significant than its effect by the enhanced turbulent mixing.
本研究将太阳辐射模型和 NO-O 光化学反应纳入带有标准 k-ε 模型的计算流体动力学 (CFD) 模拟中，以量化在二维 (2D) 街道峡谷中，混合湍流、太阳加热和化学过程对车辆被动（CO）和反应性（NO、O）污染物扩散的综合影响。考虑了各种街道纵横比（H/W=1、3、5）和太阳辐射情景（LST 0900、1200、1500）。NO 与 NO 的初始源比为 1:10，背景 O 浓度为 100 ppb（摩尔分数）。参考雷诺数约为 10-10，弗劳德数范围为 0.23 至 1.14。个人摄入量分数 (P_IF) 及其下风侧（⟨P_IF⟩）、上风侧（⟨P_IF⟩）和两侧街道（⟨P_IF⟩）的平均空间值用于评估近路建筑物中的污染物暴露情况。当 H/W=1 和 3 时，中性条件下形成顺时针单涡。LST 0900/1200 下风/地面太阳加热略微增强了这种涡旋并降低了 ⟨P_IF⟩。然而，当 H/W=3 时，上风加热在 LST 1500 下将单主导涡旋分离成两个反向旋转的涡旋，因此这种 ⟨P_IF⟩明显大于中性情况。当 H/W=5 时，中性条件下出现较低的二次逆时针涡旋，导致风较弱且行人水平浓度极高。这种双主涡结构被下风/地面加热破坏成单主涡模式，但被上风加热分解成三个反向旋转的涡旋。这三个辐射情景将中性情况下行人水平速度提高了约两个数量级，并将整体 ⟨P_IF⟩降低了两个数量级至一个数量级。对于所有情况，NO 暴露量一般比被动 CO 暴露量高 40%-380%，这表明在目前的 NO-O 滴定相互作用中，NO 通过消耗 O 转化为 NO 是主导因素。最后，太阳加热仅将空气温度提高了 2-3 K，并对化学反应速率产生轻微影响，因此对反应性污染物扩散的影响不如增强的混合湍流的影响显著。
