Direct Observations of Atmospheric Transport and Stratosphere-Troposphere Exchange from High-Precision Carbon Dioxide and Carbon Monoxide Profile Measurements

The balloon-borne Aircore campaign was conducted in Inner Mongolia, China, on June 13 and 14 2018, which detected carbon dioxide (CO 2 ) and carbon monoxide (CO) profiles from surface to 24 km, showing strong positive and negative correlations between 8 km and 10 km on 13 and 14 June, respectively. Backward trajectories, meteorological analyses, and CO 2 horizontal distributions were combined to interpret this phenomenon. The results indicated that the source region experienced a stratospheric intrusion and exhibited a large horizontal CO 2 gradient; namely, lower CO concentrations corresponded to higher CO 2 concentrations and vice versa. The laminar structure with multiple origins resulted in the highly negative correlation between CO 2 and CO in the upper troposphere on 14 June. The contribution of stratospheric air mass to the upper troposphere and that of tropospheric air mass to the lower stratosphere were 26.7% and 24.3%, respectively, based on a mass balance approach. Another interesting phenomenon is that CO 2 and CO concentrations increased substantially at approximately 8 km on 13 June. An analysis based on the backward trajectory implied that the air mass possibly came from anthropogenic sources. The slope of CO 2 /CO representing the anthropogenic sources was 87.3 ppm ppm −1 . In addition, the CO 2 profile showed that there was a large CO 2 gradient of 4 ppm km −1 within the boundary layer on 13 June, and this gradient disappeared on 14 June.