Impact of COVID-19 Lockdown on Surface Ozone in the Global Background Atmosphere

Surface ozone (O₃) is regarded as a ubiquitous pollutant in the atmosphere, posing significant threats to human health, as well as to plants and crops. The outbreak of Corona Virus Disease 2019 (COVID-19) at the end of 2019 and its rapid spreads in early 2020 and results in significant changes to human activities and pollutant emissions, which have notable impacts on the global atmospheric environment. Among these impacts, concentrations of O₃ precursors, such as nitrogen dioxide (NO₂) and volatile organic compounds (VOCs), undergo significant changes during the pandemic, resulting in fluctuations in global O₃ concentration levels. Data from global stations participating in World Meteorological Organization’s Global Atmosphere Watch (GAW) Program are used to analyze the surface mean O₃ concentration levels. Trends in background atmospheric surface O₃ concentrations at remote stations worldwide are examined, and a comparative analysis of surface O₃ concentrations before and after the pandemic is conducted to assess the impact of COVID-19 lockdown on surface O₃ concentrations at global stations. It indicates that background atmospheric surface O₃ concentrations in remote regions globally exhibit a relatively stable trend from 2010 to 2019, with a significant decline observed after 2019. Specifically, in mid-high latitudes of the Northern Hemisphere, surface O₃ concentrations at global observation stations in remote areas are found to be higher in spring and summer, while lower in autumn and winter. Conversely, stations located in mid-high latitudes of the Southern Hemisphere exhibit significantly less fluctuation in surface O₃ concentrations compared to those in the Northern Hemisphere, with trends remaining largely stable. Notably, surface O₃ concentrations at observation stations in remote areas of the Southern Hemisphere peak between June and September. Due to anthropogenic and climatic factors, the Southern Hemisphere’s O₃ concentrations are only minimally affected by the reduction in pollutant emissions, including nitrogen oxides, resulting from COVID-19 lockdown polynomial fitting analysis indicates that surface O₃ concentrations at monitoring stations in remote areas of the Southern Hemisphere do not exhibit a significant downward trend in 2020. In equatorial and adjacent regions, excluding global stations affected by monsoons, surface O₃ concentrations show minimal annual variation. When comparing surface O₃ concentrations from 2020 to those recorded between 2010 and 2019, a slight decrease is observed. However, due to the complexity of factors contributing to O₃ concentration fluctuations and the limited number of monitoring stations in equatorial regions, the overall causes for this decrease remain uncertain. The study provides insights into the impact of COVID-19 lockdown on global surface O₃ concentrations and underscores the necessity for further research to enhance our understanding of factors influencing O₃ levels across various regions of the world.