Lessons from COVID-19 and Seoul: Effects of Reduced Human Activity from Social Distancing on Urban CO2 Concentration and Air Quality

Abstract

Social restriction in cities to curb infection rates of COVID-19 has become an opportunity to investigate the relationship between humans and the urban atmosphere. We evaluate the impact of the decline in human activities as a result of social distancing on the urban CO₂ concentrations and air quality in Seoul during February and March of 2020 compared to 2019. Due to the reduction in human activity in 2020, local measurements of CO and NO₂ show a decrease in background concentration (up to –11.9% and –41.7%, respectively) and urban enhancement (up to –16.7% and –38.1%, respectively) compared to the previous year. In contrast, the background concentration of CO₂ increases by 3.9% in 2020. Ratios of CO:CO₂ and NO₂:CO₂ also show a decrease in 2020 compared to the previous year, signaling an improvement in the urban air quality of Seoul. Moreover, the insignificant change in wind speed and wind direction during the months of February and March 2020 compared to 2019 implies that CO₂, CO, and NO₂ concentrations have not been influenced by meteorological conditions, but mainly by changes in emissions from decreased human activity. Despite the rise in background CO₂ concentration, urban contributions of CO₂ show a decline of –12.6%, indicating that cities with high emissions have the potential to reduce urban CO₂ enhancements and air pollutant concentrations, and ultimately impact the global atmosphere.