Short-term reduction of regional enhancement of atmospheric CO2 in China during the first COVID-19 pandemic period

Recent studies have reported a 9% decrease in global carbon emissions during the COVID-19 lockdown period; however, its impact on the variation of atmospheric CO2 level remains under question. Using atmospheric CO2 observed at Anmyeondo station (AMY) in South Korea, downstream of China, this study examines whether the decrease in China's emissions due to COVID-19 can be detected from the enhancement of CO2 mole fraction (Delta CO2) relative to the background value. The Weather Research and Forecasting-Stochastic Time-Inverted Lagrangian Transport model was applied to determine when the observed mole fractions at AMY were affected by air parcels from China. Atmospheric observations at AMY showed up to a -20% (-1.92 ppm) decrease in Delta CO2 between February and March 2020 compared to the same period in 2018 and 2019, particularly with a -34% (-3.61 ppm) decrease in March. Delta CO, which was analyzed to explore the short-term effect of emission reductions, had a decrease of -43% (-80.66 ppb) during the lockdown in China. Particularly in East China, where emissions are more concentrated than in Northeast China, Delta CO2 and Delta CO decreased by -44% and -65%, respectively. The Delta CO/Delta CO2 ratio (24.8 ppb ppm(-1)), which is the indicator of emission characteristics, did not show a significant difference before and after the COVID-19 lockdown period (alpha = 0.05), suggesting that this decrease in Delta CO2 and Delta CO was associated with emission reductions rather than changes in emission sources or combustion efficiency in China. Reduced carbon emissions due to limited human activity resulted in a decrease in the short-term regional enhancement to the observed atmospheric CO2.