Reduction in urban atmospheric CO2 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 CO2 concentrations because of the complex cycles involving the interaction of CO2 with the natural environment. In this study, we compared the changes in urban CO2 enhancement (△CO2) reflecting the contribution of local CO2 emissions to the atmospheric CO2 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 CO2 ground observation sites in the central area of Seoul and outside the urban area of Seoul. By comparing the urban CO2 concentration in Seoul with that of the background area using two different methods, considering both vertical and horizontal differences in CO2 concentration, we quantified the △CO2 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 △CO2 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 CO2 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 CO2 emissions, leading to a reduction in atmospheric CO2 concentration. Interestingly, it also shows that the extent of atmospheric CO2 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 CO2 concentration helping to further mitigate climate change.