The dynamics of CO₂ has received considerable attention in the literature, yet uncertainties remain. We applied an online coupled weather-biosphere model to simulate biosphere processes and meteorology simultaneously to characterize CO₂ dynamics in China. Anthropogenic emission was more influential in upper air, and the biosphere flux played a more important role in surface CO₂, suggesting a significant influence of the boundary layer thermal structure on the accumulation and depletion of CO₂.