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Elucidating the mechanisms of rapid O3  increase in North China Plain during COVID-19 lockdown period            
  • Rui Li,
  • Yining Gao,
  • Gehui Wang
Rui Li
East China Normal University

Corresponding Author:[email protected]

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Yining Gao
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Gehui Wang
East China Normal University
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Ozone (O3) levels in North China Plain (NCP) suffered from rapid increases during the COVID-19 period. Many previous studies have confirmed more rapid NOx reduction compared with VOCs might be responsible for the O3 increase during this period, while the comprehensive impacts of each VOC species and NOx on ambient O3 and their interactions with meteorology were not revealed clearly. To clarify the detailed reasons for the O3 increase, a continuous campaign was performed in a typical industrial city of NCP. Meanwhile, the machine-learning technique and the box model were employed to reveal the mechanisms of O3 increase from the perspective of meteorology and photochemical process, respectively. The result suggested that the ambient O3 level in Tangshan increased from 18.7 ± 4.63 to 45.6 ± 8.52 μg/m3 (143%) after COVID-19 lockdown, and the emission reduction and meteorology contributed to 77% and 66% of this increment, respectively. The higher wind speed (WS) coupled with regional transport played a significant role on O3 increase (30.8 kg/s). The O3 sensitivity verified that O3 production was highly volatile organic compounds (VOC)-sensitive (Relative incremental reactivity (RIR): 0.75), while the NOx showed the negative impact on O3 production in Tangshan (RIR: -0.59). It suggested that the control of VOCs rather than NOx might be more effective in reducing O3 level in Tangshan because it was located on the VOC-limited regime. Besides, both of ozone formation potential (OFP) analysis and observation-based model (OBM) demonstrated that the alkenes (36.3 ppb) and anthropogenic oxygenated volatile organic compounds (OVOCs) (15.2 ppb) showed the higher OFP compared with other species, and their reactions released a large number of HO2 and RO2 radicals. Moreover, the concentrations of these species did not experience marked decreases after COVID-19 lockdown, which were major contributors to O3 increase during this period. This study underlines the necessity of priority controlling alkenes and OVOCs, which will benefit not just NCP but also other regions in China.
27 Mar 2023Submitted to ESS Open Archive
04 Apr 2023Published in ESS Open Archive