Effect of COVID-19 Response Policy on Air Quality: A Study in South China Context.

Mass suspension of anthropogenic activities is extremely rare, the quarantine due to the coronavirus disease 2019 (COVID-19) represents a natural experiment to investigate the impact of anthropogenic activities on air quality. The mitigation of air pollution during the COVID-19 lockdown has been reported from a global perspective; however, the air pollution levels vary in different regions. This study initiated a novel synthesis of multiple-year satellite observations, national ground measurements towards SO₂, NO₂ and O₃ and meteorological conditions to evaluate the impact of the COVID-19 lockdown in Beihai, a specific city in a less developed area in southwest China, to reveal the potential implications of control strategies for air pollution. The levels of the major air pollutants during the COVID-19 lockdown (LP) and during the same period of previous years (SP) were compared and a series of statistical tools were applied to analyze the sources of air pollution in Beihai. The results show that air pollutant levels decreased with substantial diversity during the LP. Satellite-retrieved NO₂ and SO₂ levels during the LP decreased by 5.26% and 22.06%, while NO₂, SO₂, PM_2.5 and PM₁₀ from ground measurements during the LP were 25.6%, 2.7%, 22.2% and 22.2% lower than during SP, respectively. Ground measured SO₂ concentrations during the LP were only 2.7% lower than during the SP, which may be attributed to uninterrupted essential industrial activities, such as power plants. Polar plots analysis shows that NO₂ concentrations were strongly associated with local emission sources, such as automobiles and local industry. Additionally, the much lower levels of NO₂ concentrations during the LP and the absence of an evening peak may highlight the significant impact of the traffic sector on NO₂. The decrease in daily mean O₃ concentrations during the LP may be associated with the reduction in NO₂ concentrations. Indications in this study could be beneficial for the formulation of atmospheric protection policies. [ABSTRACT FROM AUTHOR]