Zheng Xi, Meng Haiyan, Tan Qinwen, Zhou Zihang, Zhou Xiaoling, Liu Xuan, Grieneisen Michael L, Wang Nan, Zhan Yu, Yang Fumo
Department of Environmental Science and Engineering, Sichuan University, Chengdu, Sichuan 610065, China.
Chengdu Academy of Environmental Sciences, Chengdu, Sichuan 610072, China.
Sci Total Environ. 2024 Nov 1;949:175073. doi: 10.1016/j.scitotenv.2024.175073. Epub 2024 Jul 30.
Emissions of nitrogen oxides (NOx) are a dominant contributor to ambient nitrogen dioxide (NO) concentrations, but the quantitative relationship between them at an intracity scale remains elusive. The Chengdu 2021 FISU World University Games (July 22 to August 10, 2023) was the first world-class multisport event in China after the COVID-19 pandemic which led to a substantial decline in NOx emissions in Chengdu. This study evaluated the impact of variations in NOx emissions on NO concentrations at a fine spatiotemporal scale by leveraging this event-driven experiment. Based on ground-based and satellite observations, we developed a data-driven approach to estimate full-coverage hourly NO concentrations at 1 km resolution. Then, a random-forest-based meteorological normalization method was applied to decouple the impact of meteorological conditions on NO concentrations for every grid cell, the resulting data were then compared with the timely bottom-up NOx emissions. The SHapley-Additive-exPlanation (SHAP) method was employed to delineate the individual contributions of meteorological factors and various emission sources to the changes in NO concentrations. According to the full-coverage meteorologically normalized NO concentrations, a decrease in NOx emissions and favorable meteorological conditions accounted for 80 % and 20 % of the NO reduction, respectively, across Chengdu city during the control period. Within the strict control zone, a 30 % decrease in the meteorologically normalized NO concentrations was observed during the control period. The normalized NO concentrations demonstrated a strong correlation with NOx emissions (R = 0.96). Based on the SHAP analysis, traffic emissions accounted for 73 % of the reduction in NO concentrations, underscoring the significance of traffic control measures in improving air quality in urban areas. This study provides insights into the relationship between NO concentrations and NOx emissions using real-world data, which implies the substantial benefits of vehicle electrification for sustainable urban development.
氮氧化物（NOx）排放是环境中二氧化氮（NO）浓度的主要贡献者，但它们在城市尺度上的定量关系仍不明确。成都2021年世界大学生运动会（2023年7月22日至8月10日）是新冠疫情后中国举办的首个世界级多项目体育赛事，该赛事导致成都的NOx排放量大幅下降。本研究利用这一事件驱动的实验，在精细的时空尺度上评估了NOx排放变化对NO浓度的影响。基于地面和卫星观测，我们开发了一种数据驱动的方法，以1公里分辨率估算全区域每小时的NO浓度。然后，应用基于随机森林的气象归一化方法，消除气象条件对每个网格单元中NO浓度的影响，将所得数据与及时的自下而上的NOx排放数据进行比较。采用SHapley加性解释（SHAP）方法，描述气象因素和各种排放源对NO浓度变化的个体贡献。根据全区域气象归一化后的NO浓度，在管控期内，成都全市NOx排放减少和有利的气象条件分别占NO减少量的80%和20%。在严格管控区内，管控期内气象归一化后的NO浓度下降了30%。归一化后的NO浓度与NOx排放呈现出很强的相关性（R = 0.96）。基于SHAP分析，交通排放占NO浓度下降量的73%，这突出了交通管制措施对改善城市空气质量的重要性。本研究利用实际数据深入探讨了NO浓度与NOx排放之间的关系，这意味着车辆电气化对城市可持续发展具有巨大益处。
