Reduction in urban atmospheric CO(2) enhancement in Seoul, South Korea, resulting from social distancing policies during the COVID-19 pandemic

With the spread of the COVID-19 virus globally, cities worldwide have implemented unprecedented social distancing policies to mitigate infection rates. Many studies have demonstrated that improved air quality and reduced carbon emissions have resulted from the COVID-19 pandemic. Yet, questions remain regarding changes in atmospheric CO(2) concentrations because of the complex cycles involving the interaction of CO(2) with the natural environment. In this study, we compared the changes in urban CO(2) enhancement (△CO(2)) reflecting the contribution of local CO(2) emissions to the atmospheric CO(2) in urban areas, according to the intensity of social distancing policies implemented during the COVID-19 pandemic in Seoul, South Korea. We used data from three CO(2) ground observation sites in the central area of Seoul and outside the urban area of Seoul. By comparing the urban CO(2) concentration in Seoul with that of the background area using two different methods, considering both vertical and horizontal differences in CO(2) concentration, we quantified the △CO(2) of the pre-COVID-19 period and two COVID-19 periods, during which intensive social distancing policies with different intensities were implemented (Level 1, Level 2.5). During the pre-COVID-19 period, the average △CO(2) calculated using the two methods was 24.82 ppm, and it decreased significantly to 16.42 and 14.36 ppm during the Level 1 and Level 2.5 periods, respectively. In addition, the urban contribution of Seoul to atmospheric CO(2) concentration decreased from 5.27% during the pre-COVID-19 period to 3.54% and 3.19% during the Level 1 and Level 2.5 periods, respectively. The results indicate that the social distancing policies implemented in Seoul resulted in reduced local CO(2) emissions, leading to a reduction in atmospheric CO(2) concentration. Interestingly, it also shows that the extent of atmospheric CO(2) concentration reduction can be greatly affected by the intensity of policies. Our study suggests that changes in human activity could reduce the urban direct contribution to the background CO(2) concentration helping to further mitigate climate change.