Carbon balance of China constrained by CONTRAIL aircraft CO₂ measurements

Abstract. Terrestrial carbon dioxide (CO₂) flux estimates in China using atmospheric inversion method are beset with considerable uncertainties because very few atmospheric CO₂ concentration measurements are available. In order to improve these estimates, nested atmospheric CO₂ inversion during 2002–2008 is performed in this study using passenger aircraft-based CO₂ measurements over Eurasia from the Comprehensive Observation Network for Trace gases by Airliner (CONTRAIL) project. The inversion system includes 43 regions with a focus on China, and is based on the Bayesian synthesis approach and the TM5 transport model. The terrestrial ecosystem carbon flux modeled by the Boreal Ecosystems Productivity Simulator (BEPS) model and the ocean exchange simulated by the OPA-PISCES-T model are considered as the prior fluxes. The impacts of CONTRAIL CO₂ data on inverted China terrestrial carbon fluxes are quantified, the improvement of the inverted fluxes after adding CONTRAIL CO₂ data are rationed against climate factors and evaluated by comparing the simulated atmospheric CO₂ concentrations with three independent surface CO₂ measurements in China. Results show that with the addition of CONTRAIL CO₂ data, the inverted carbon sink in China increases while those in South and Southeast Asia decrease. Meanwhile, the posterior uncertainties over these regions are all reduced (2–12%). CONTRAIL CO₂ data also have a large effect on the inter-annual variation of carbon sinks in China, leading to a better correlation between the carbon sink and the annual mean climate factors. Evaluations against the CO₂ measurements at three sites in China also show that the CONTRAIL CO₂ measurements may have improved the inversion results.