The influence of cold fronts on the formation of ozone (O3) pollution, particularly the contributions of physical and chemical processes to O3 abundance during the passage of cold fronts in winter over the Pearl River Estuary (PRE) region was still unclear. This study provided an in-depth analysis on the occurrence of high O3 pollution based on data from field measurements and simulation of a chemical transport model (i.e., WRF-Chem) over the PRE region during winter 2021 when cold fronts were frequently observed. Totally 7 high O3 episode days were observed during pre- and post-frontal stages at DWS (i.e., Da Wan Shan island), a downwind island site of the inland Pearl River Delta (PRD) region, which were accompanied with the prevailing northerly wind patterns with insignificant variations of wind speeds in a stable boundary layer over the whole PRE region. The quantitative analysis based on simulation results indicated that horizontal transport and chemical processes accounted for the buildup of O3 abundance at DWS, with the highest mean rates of 7.3 and 5.6 ppbv/h at pre- and post-frontal stages, respectively. The high contributions from horizontal transport to O3 levels at DWS were associated with the persistent northerly winds with small variations, while the contributions of chemical processes were varied with the abundance of precursors and meteorological conditions. However, vertical transport made negative contributions to O3 abundance, with the most significant mean diffusion rate of −2.6 ppbv/h at the frontal stage because of the control of high-pressure system, while the less influence of vertical transport at pre- and post-frontal stages was associated with the weak pressure gradient forces and wind patterns. The sensitivity analysis further demonstrated that the emissions of precursors from the inland PRD region contributed 50–76% to O3 abundance over PRE at different stages. Overall, the above results quantitatively confirmed the dominant role of transport from inland PRD to the O3 pollution over the downwind PRE region and were helpful for better understanding of O3 pollution in winter over PRE.

中文翻译：

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冷锋过境珠江口引发高O3污染


冷锋对臭氧（O3）污染形成的影响，特别是冬季冷锋经过珠江口（PRE）地区期间物理和化学过程对O3丰度的贡献仍不清楚。本研究基于 2021 年冬季冷锋频繁观测到的 PRE 地区的现场测量数据和化学输运模型（即 WRF-Chem）模拟，对高 O3 污染的发生进行了深入分析。珠江三角洲内陆地区的下风岛DWS（即大湾山岛）在锋锋前后阶段共观察到7个高O3发作日，盛行偏北风整个 PRE 区域稳定边界层中风速变化不显着的模式。基于模拟结果的定量分析表明，水平传输和化学过程导致了 DWS 中 O3 丰度的积累，在额叶前和额叶后阶段，最高平均速率分别为 7.3 和 5.6 ppbv/h。 DWS 水平输送对 O3 水平的高贡献与变化较小的持续偏北风有关，而化学过程的贡献则随前体丰度和气象条件的变化而变化。然而，垂直输送对O3丰度的影响较小，由于高压系统的控制，在额叶阶段平均扩散速率最显着，为-2.6 ppbv/h，而前后垂直输送影响较小。 -额叶阶段与弱压力梯度力和风型有关。 敏感性分析进一步表明，珠三角内陆地区前体排放量对不同阶段PRE的O3丰度贡献率达到50%~76%。总体而言，上述结果定量证实了珠三角内陆输送对PRE下风区O3污染的主导作用，有助于更好地了解PRE冬季O3污染。