State Key Laboratory of Organic Geochemistry, Guangdong Key Laboratory of Environmental Protection and Resources Utilization, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China; Guangzhou Sub-branch of Guangdong Ecological and Environmental Monitoring Center, Guangzhou 510060, China; University of Chinese Academy of Sciences, Beijing 100049, China.
State Key Laboratory of Organic Geochemistry, Guangdong Key Laboratory of Environmental Protection and Resources Utilization, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China; Guangdong Provincial Academy of Environmental Sciences, Guangzhou 510045, China.
Sci Total Environ. 2022 Jun 1;823:153720. doi: 10.1016/j.scitotenv.2022.153720. Epub 2022 Feb 8.
During the COVID-19 lockdown, ambient ozone levels are widely reported to show much smaller decreases or even dramatical increases under substantially reduced precursor NOx levels, yet changes in ambient precursor volatile organic compounds (VOCs) have been scarcely reported during the COVID-19 lockdown, which is an opportunity to examine the impacts of dramatically changing anthropogenic emissions on ambient VOC levels in megacities where ozone formation is largely VOC-limited. In this study, ambient VOCs were monitored online at an urban site in Guangzhou in the Pearl River Delta region before, during, and after the COVID-19 lockdown. The average total mixing ratios of VOCs became 19.1% lower during the lockdown than before, and those of alkanes, alkenes and aromatics decreased by 19.0%, 24.8% and 38.2%, respectively. The levels of light alkanes (C < 6) decreased by only 13.0%, while those of higher alkanes (C ≥ 6) decreased by 67.8% during the lockdown. Disappeared peak VOC levels in morning rush hours and the drop in toluene to benzene ratios during the lockdown suggested significant reductions in vehicle exhaust and industrial solvent emissions. Source apportioning by positive matrix factorization model revealed that reductions in industrial emissions, diesel exhaust (on-road diesel vehicles and off-road diesel engines) and gasoline-related emissions could account for 48.9%, 42.2% and 8.8%, respectively, of the decreased VOC levels during the lockdown. Moreover, the reduction in industrial emissions could explain 56.0% and 70.0% of the reductions in ambient levels of reactive alkenes and aromatics, respectively. An average increase in O-1 h by 17% and a decrease in the daily maximum 8-h average ozone by 11% under an average decrease in NOx by 57.0% and a decrease in VOCs by 19.1% during the lockdown demonstrated that controlling emissions of precursors VOCs and NOx to prevent ambient O pollution in megacities such as Guangzhou remains a highly challenging task.
在 COVID-19 封锁期间，据广泛报道，在大量减少前体氮氧化物（NOx）水平的情况下，环境臭氧水平下降幅度较小甚至出现显著增加，但在 COVID-19 封锁期间，环境前体挥发性有机化合物（VOCs）的变化却鲜有报道，这是一个机会，可以在臭氧形成主要受 VOC 限制的特大城市中，考察人为排放急剧变化对环境 VOC 水平的影响。在这项研究中，在 COVID-19 封锁之前、期间和之后，在珠江三角洲地区的广州市的一个城市站点在线监测了环境 VOCs。与封锁前相比，封锁期间 VOC 的总混合比平均降低了 19.1%，烷烃、烯烃和芳烃的浓度分别降低了 19.0%、24.8%和 38.2%。轻烷烃（C < 6）的浓度仅下降了 13.0%，而高烷烃（C ≥ 6）的浓度则下降了 67.8%。封锁期间早高峰时段 VOC 峰值消失以及甲苯与苯的比值下降表明，车辆尾气和工业溶剂排放显著减少。正矩阵因子分解模型的源分配表明，工业排放、柴油尾气（道路柴油车辆和非道路柴油发动机）和汽油相关排放的减少分别可以解释封锁期间 VOC 水平下降的 48.9%、42.2%和 8.8%。此外，工业排放的减少可以解释环境中反应性烯烃和芳烃浓度下降的 56.0%和 70.0%。在平均 NOx 下降 57.0%和 VOCs 下降 19.1%的情况下，O-1 h 的平均增加了 17%，日最大 8 小时平均臭氧浓度下降了 11%，这表明在特大城市（如广州）控制 VOCs 和 NOx 前体排放以防止大气 O3 污染仍然是一项极具挑战性的任务。
