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

Umezawa, Taku; Matsueda, Hidekazu; Sawa, Yousuke; Niwa, Yosuke; Machida, Toshinobu; Zhou, Lingxi

Measurement of atmospheric carbon dioxide (inline-formulaCO2) is indispensable for top-down estimation of surface inline-formulaCO2 sources/sinks by an atmospheric transport model. Despite the growing importance of Asia in the global carbon budget, the region has only been sparsely monitored for atmospheric inline-formulaCO2 and our understanding of atmospheric inline-formulaCO2 variations in the region (and thereby that of the regional carbon budget) is still limited. In this study, we present climatological inline-formulaCO2 distributions over the Asia-Pacific region obtained from the CONTRAIL (Comprehensive Observation Network for TRace gases by AIrLiner) measurements. The high-frequency in-flight inline-formulaCO2 measurements over 10 years reveal a clear seasonal variation in inline-formulaCO2 in the upper troposphere (UT), with a maximum occurring in April–May and a minimum in August–September. The inline-formulaCO2 mole fraction in the UT north of 40inline-formula N is low and highly variable in June–August due to the arrival of air parcels with seasonally low inline-formulaCO2 caused by the summertime biospheric uptake in boreal Eurasia. For August–September in particular, the UT inline-formulaCO2 is noticeably low within the Asian summer monsoon anticyclone associated with the convective transport of strong biospheric inline-formulaCO2 uptake signal over South Asia. During September as the anticyclone decays, a spreading of this low-inline-formulaCO2 area in the UT is observed in the vertical profiles of inline-formulaCO2 over the Pacific Rim of continental East Asia. Simulation results identify the influence of anthropogenic and biospheric inline-formulaCO2 fluxes in the seasonal evolution of the spatial inline-formulaCO2 distribution over the Asia-Pacific region. It is inferred that a substantial contribution to the UT inline-formulaCO2 over the northwestern Pacific comes from continental East Asian emissions in spring; but in the summer monsoon season, the prominent air mass origin switches to South Asia and/or Southeast Asia with a distinct imprint of the biospheric inline-formulaCO2 uptake. The CONTRAIL inline-formulaCO2 data provide useful constraints to model estimates of surface fluxes and to the evaluation of the satellite observations, in particular for the Asia-Pacific region.



Umezawa, Taku / Matsueda, Hidekazu / Sawa, Yousuke / et al: Seasonal evaluation of tropospheric CO2 over the Asia-Pacific region observed by the CONTRAIL commercial airliner measurements. 2018. Copernicus Publications.


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