The contribution of NO_x emissions and background O₃ to the sources and partitioning of the oxidants [OX (= O₃ + NO₂)] at the Marylebone Road site in London during the 2000s and 2010s has been investigated to see the impact of the control measures or technology changes inline with the London Mayor’s Air Quality Strategy. The abatement of the pollution emissions has an impact on the trends of local and background oxidants, [OX]_L and [OX]_B, decreasing by 1.4% per year and 0.4% per year, respectively from 2000 to 2019. We also extend our study to three roadside sites (Din Daeng, Thonburi and Chokchai) in another megacity, Bangkok, to compare [OX]_L and [OX]_B and their behavioural changes with respect to the Marylebone Road site. [OX]_L and [OX]_B at the Marylebone Road site (0.21[NO_x] and 32 ppbv) are comparable with the roadside sites of Thailand (0.12[NO_x] to 0.26[NO_x] and 29 to 32 ppbv). The seasonal variation of [OX]_B levels displays a spring maximum for London, which is due to the higher northern hemispheric ozone baseline, but a maximum during the dry season is found for Bangkok which is likely due to regional-scale long-range transport from the Asian continent. The diurnal variations of [OX]_L for both London and Bangkok roadside sites confirm the dominance of the oxidants from road transport emissions, which are found to be higher throughout the daytime. WRF-Chem-CRI model simulations of the distribution of [OX] showed that the model performed well for London background sites when predicting [OX] levels compared with the measured [OX] levels suggesting that the model is treating the chemistry of the oxidants correctly. However, there are large discrepancies for the model–measurement [OX] levels at the traffic site because of the difficulties in the modelling of [OX] at large road networks in megacities for the complex sub grid-scale dynamics that are taking place, both in terms of atmospheric processes and time-varying sources, such as traffic volumes. For roadside sites in Bangkok, the trend in changes of [OX] is predicted by the model correctly but overestimated in absolute magnitude. We suggest that this large deviation is likely to be due to discrepancies in the EDGAR emission inventory (emission overestimates) beyond the resolution of the model.

中文翻译：

---

调查伦敦和曼谷氧化剂的背景和当地贡献

NO的贡献_X排放量和背景Ò ₃到源和氧化剂分隔[OX（= O ₃ + NO ₂）]在2000年代和2010年代期间在伦敦马里波恩路站点已研究看的冲击控制措施或技术变化符合伦敦市长的空气质量战略。从2000年到2019年，污染排放的减少对本地和背景氧化剂[OX] _L和[OX] _B的趋势产生了影响，分别每年减少1.4％和0.4％。研究了另一个特大城市曼谷的三个路边站点（Din Daeng，吞武里和Chokchai），以比较[OX] _L和[OX]_B及其相对于马里波恩路遗址的行为变化。马里波恩路站点的[OX] _L和[OX] _B（0.21 [NO _x ]和32 ppbv）与泰国的路边站点相当（0.12 [NO _x ]至0.26 [NO _x ]和29至32 ppbv） 。[OX] _B含量的季节性变化显示伦敦的春季最大值，这是由于北半球臭氧基线较高，但曼谷的干旱季节则出现了最大值，这很可能是由于区域范围的远程运输所致来自亚洲大陆。[OX] _L的日变化伦敦和曼谷的路边站点都证实了道路运输排放中氧化剂的主导地位，发现白天的氧化剂含量更高。WRF-Chem-CRI模型对[OX]的分布的模拟表明，与预测的[OX]含量相比，该模型在预测[OX]含量时在伦敦背景场所表现良好，表明该模型正在正确处理氧化剂的化学物。但是，由于正在发生的复杂子网格规模动态，在大城市的大型道路网对[OX]建模的困难，交通站点的模型[OX]级别存在很大差异。就大气过程和时变源（例如交通量）而言。对于曼谷的路边站点，该模型可以正确预测[OX]的变化趋势，但绝对幅度过高。我们建议，这种较大的偏差可能是由于EDGAR排放清单中的差异（排放过高估计）所致，超出了模型的分辨率。