Near-real-time estimation of fossil fuel CO emissions from China based on atmospheric observations on Hateruma and Yonaguni Islands, Japan.

Unlabelled: We developed a near-real-time estimation method for temporal changes in fossil fuel CO (FFCO) emissions from China for 3 months [January, February, March (JFM)] based on atmospheric CO and CH observations on Hateruma Island (HAT, 24.06° N, 123.81° E) and Yonaguni Island (YON, 24.47° N, 123.01° E), Japan. These two remote islands are in the downwind region of continental East Asia during winter because of the East Asian monsoon. Previous studies have revealed that monthly averages of synoptic-scale variability ratios of atmospheric CO and CH (ΔCO/ΔCH) observed at HAT and YON in JFM are sensitive to changes in continental emissions. From the analysis based on an atmospheric transport model with all components of CO and CH fluxes, we found that the ΔCO/ΔCH ratio was linearly related to the FFCO/CH emission ratio in China because calculating the variability ratio canceled out the transport influences. Using the simulated linear relationship, we converted the observed ΔCO/ΔCH ratios into FFCO/CH emission ratios in China. The change rates of the emission ratios for 2020-2022 were calculated relative to those for the preceding 9-year period (2011-2019), during which relatively stable ΔCO/ΔCH ratios were observed. These changes in the emission ratios can be read as FFCO emission changes under the assumption of no interannual variations in CH emissions and biospheric CO fluxes for JFM. The resulting average changes in the FFCO emissions in January, February, and March 2020 were 17 ± 8%, - 36 ± 7%, and - 12 ± 8%, respectively, (- 10 ± 9% for JFM overall) relative to 2011-2019. These results were generally consistent with previous estimates. The emission changes for January, February, and March were 18 ± 8%, - 2 ± 10%, and 29 ± 12%, respectively, in 2021 (15 ± 10% for JFM overall) and 20 ± 9%, - 3 ± 10%, and - 10 ± 9%, respectively, in 2022 (2 ± 9% for JFM overall). These results suggest that the FFCO emissions from China rebounded to the normal level or set a new high record in early 2021 after a reduction during the COVID-19 lockdown. In addition, the estimated reduction in March 2022 might be attributed to the influence of a new wave of COVID-19 infections in Shanghai.

Supplementary Information: The online version contains supplementary material available at 10.1186/s40645-023-00542-6.