Seasonal Variation of Atmospheric CO ₂ Concentration in China and Indo‐China Peninsula and Their Mutual Impacts

Abstract Quantifying the interregional transport of atmospheric carbon dioxide (CO 2 ) between Indo‐China Peninsula and the Chinese mainland is of significant importance for the carbon budget accounting. However, few studies have addressed the mutual impacts of atmospheric CO 2 between the two regions. In this study, a regional atmospheric transport model (WRF‐RAQMS) coupled CO 2 physical processes was applied to investigate the seasonal variation of atmospheric CO 2 concentrations over the Indo‐China Peninsula and Chinese mainland, and to reveal the mutual impacts between the two regions by taking the year 2020, when COVID‐19 occurred, as an exemplification. The simulated atmospheric CO 2 concentrations in the study domain exhibited distinct seasonal variation, and higher concentrations occurred in spring and winter with regional average exceeding 413.0 ppm, and the lowest concentration appeared in autumn, which were generally consistent with results from multi‐source validation data sets. The daily variations and three‐dimensional spatial distribution of net changes in atmospheric CO 2 concentrations across the four seasons were also reproduced. The impacts of the anthropogenic activities and natural biomass burning in Indo‐China Peninsula on the tropospheric CO 2 concentrations over the Chinese mainland decreased gradually from spring to winter at 24.13%, 5.02%, 3.64%, and 0.92%, respectively, with the majority contributions originated from biomass burning. Conversely, the most significant impacts of the anthropogenic activities and natural biomass burning in Chinese mainland on the tropospheric CO 2 concentrations over Indo‐China Peninsula were occurred in winter (13.35%) and almost all CO 2 transported from the Chinese mainland to the Indo‐China Peninsula originated from anthropogenic emissions.