Analysis of CO 2 spatio-temporal variations in China using a weather–biosphere online coupled model

Abstract. The dynamics of atmospheric CO2 has received considerable attention in the literature, yet significant uncertainties remain within the\nestimates of contribution from the terrestrial flux and the influence of atmospheric mixing. In this study we apply the WRF-Chem model configured with\nthe Vegetation Photosynthesis and Respiration Model (VPRM) option for biomass fluxes in China to characterize the dynamics of CO2 in the\natmosphere. The online coupled WRF-Chem model is able to simulate biosphere processes (photosynthetic uptake and ecosystem respiration) and meteorology in\none coordinate system. We apply WRF-Chem for a multi-year simulation (2016–2018) with integrated data from a satellite product, flask samplings,\nand tower measurements to diagnose the spatio-temporal variations of CO2 fluxes and concentrations in China. We find that the spatial\ndistribution of CO2 was dominated by anthropogenic emissions, while its seasonality (with maxima in April 15  ppmv higher than\nminima in August) was dominated by the terrestrial flux and background CO2 . Observations and simulations revealed a consistent increasing\ntrend in column-averaged CO2 ( XCO2 ) of 2.46  ppmv (0.6  % yr−1 ) resulting from anthropogenic emission\ngrowth and biosphere uptake. WRF-Chem successfully reproduced ground-based measurements of surface CO2 concentration with a mean bias of\n − 0.79  ppmv and satellite-derived XCO2 with a mean bias of 0.76  ppmv . The model-simulated seasonality was also consistent\nwith observations, with correlation coefficients of 0.90 and 0.89 for ground-based measurements and satellite data, respectively. Tower observations\nfrom a background site at Lin\u0027an (30.30 ∘  N, 119.75 ∘  E) revealed a strong correlation ( − 0.98) between vertical CO2 and\ntemperature gradients, suggesting a significant influence of boundary layer thermal structure on the accumulation and depletion of atmospheric\n CO2 .