Detection of fossil-fuel CO2 plummet in China due to COVID-19 by observation at Hateruma

The COVID-19 pandemic caused drastic reductions in carbon dioxide (CO 2 ) emissions, but due to its large atmospheric reservoir and long lifetime, no detectable signal has been observed in the atmospheric CO 2 growth rate. Using the variabilities in CO 2 (ΔCO 2 ) and methane (ΔCH 4 ) observed at Hateruma Island, Japan during 1997–2020, we show a traceable CO 2 emission reduction in China during February–March 2020. The monitoring station at Hateruma Island observes the outflow of Chinese emissions during winter and spring. A systematic increase in the ΔCO 2 /ΔCH 4 ratio, governed by synoptic wind variability, well corroborated the increase in China’s fossil-fuel CO 2 (FFCO 2 ) emissions during 1997–2019. However, the ΔCO 2 /ΔCH 4 ratios showed significant decreases of 29 ± 11 and 16 ± 11 mol mol −1 in February and March 2020, respectively, relative to the 2011–2019 average of 131 ± 11 mol mol −1 . By projecting these observed ΔCO 2 /ΔCH 4 ratios on transport model simulations, we estimated reductions of 32 ± 12% and 19 ± 15% in the FFCO 2 emissions in China for February and March 2020, respectively, compared to the expected emissions. Our data are consistent with the abrupt decrease in the economic activity in February, a slight recovery in March, and return to normal in April, which was calculated based on the COVID-19 lockdowns and mobility restriction datasets.