Carbon balance of China constrained by CONTRAIL aircraft CO<sub>2</sub> measurements

Abstract

Abstract. Terrestrial carbon dioxide (CO 2 ) flux estimates in China using atmospheric inversion method are beset with considerable uncertainties because very few atmospheric CO 2 concentration measurements are available. In order to improve these estimates, nested atmospheric CO 2 inversion during 2002-2008 is performed in this study using passenger aircraft-based CO 2 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 CON-TRAIL CO 2 data on inverted China terrestrial carbon fluxes are quantified, the improvement of the inverted fluxes after adding CONTRAIL CO 2 data are rationed against climate factors and evaluated by comparing the simulated atmospheric CO 2 concentrations with three independent surface CO 2 measurements in China. Results show that with the addition of CONTRAIL CO 2 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 CO 2 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 CO 2 measurements at three sites in China also show that the CONTRAIL CO 2 measurements may have improved the inversion results.

Seasonal evaluation of tropospheric CO<sub>2</sub> over the Asia-Pacific region observed by the CONTRAIL commercial airliner measurements

“…To estimate surface CO 2 fluxes, atmospheric transport models have been conventionally constrained by various surface measurement networks (e.g., Gurney et al, 2002;Patra et al, 2008). But due to the sparseness of the surface T. Umezawa et al: Seasonal variations of tropospheric CO 2 over Asia Pacific measurement sites in Asia, an increasing number of modeling studies that have focused on the Asian carbon budget (e.g., Patra et al, 2011;Zhang et al, 2014;Jiang et al, 2014Jiang et al, , 2016 in recent years started to incorporate CO 2 data taken by commercial airliners, such as CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container; Brenninkmeijer et al, 2007) and CONTRAIL (Comprehensive Observation Network for TRace gases by AIrLiner; . It has been demonstrated that by incorporating the CARIBIC and CONTRAIL data, model estimates of the Asian CO 2 fluxes have been significantly improved (Patra et al, 2011;Shirai et al, 2017).…”

Top–down assessment of the Asian carbon budget since the mid 1990s

“…On the basis of an Instrument Container) 13 , CONTRAIL (Comprehensive Observation Network for TRace gases by AIrLiner) 14 15 and Asian Global Atmospheric Watch (GAW) have helped ameliorate this. CARIBIC data have been utilized in an inversion for CO 2 fluxes in South Asia 16 and CONTRAIL data in inversions focusing on Asian CO 2 fluxes 17 18 19 . These inversions 16 17 18 consistently found a net sink for South Asia of −0.11 to −0.37 PgC per year (note that a negative flux is in the direction from the atmosphere to the land/ocean, that is, a sink).…”

“…CARIBIC data have been utilized in an inversion for CO 2 fluxes in South Asia 16 and CONTRAIL data in inversions focusing on Asian CO 2 fluxes 17 18 19 . These inversions 16 17 18 consistently found a net sink for South Asia of −0.11 to −0.37 PgC per year (note that a negative flux is in the direction from the atmosphere to the land/ocean, that is, a sink). In contrast, for Southeast Asia, one recent study 17 found a source of ∼0.45 PgC per year, while another 18 found a sink of ∼−0.28 PgC per year.…”

Diagnostic methods for atmospheric inversions of long-lived greenhouse gases

“…Such experiments can be used to estimate the uncertainty reduction (see Sect. 3.2) that could potentially be achieved by assimilating more observations over or downwind from poorly constrained regions as well as the effects of a more extensive observational network on the estimated spatial and temporal variability of fluxes (e.g., Butler et al, 2010;Saeki et al, 2013b;Kadygrov et al, 2015;Jiang et al, 2014;Peters et al, 2010). They can also be used to determine the value of episodic versus continuous observations (e.g., Peters et al, 2010).…”

“…More broadly, evaluation against all types of independent atmospheric observations provides an additional window into the degree to which estimated fluxes capture key features of the atmospheric signal, such as the seasonal cycle, latitudinal gradients, or regional patterns of concentrations (e.g., Zhang et al, 2014;Jiang et al, 2014;Díaz Isaac et al, 2014;Pandey et al, 2016;Liu and Bowman, 2016;Johnson et al, 2016).…”