Direct observations of atmospheric transport and stratosphere-troposphere exchange from high-precision carbon dioxide and carbon monoxide profile measurements

A new in situ measurement campaign of carbon dioxide (CO2) and carbon monoxide (CO) profiles was conducted in China on June 13 and 14, 2018. Interestingly, the derived CO and CO2 profiles were highly positively correlated on June 13 and highly negatively correlated on June 14 in the upper troposphere between 8 and 10 km. Backward trajectories, meteorological analyses, and CO2 horizontal distributions were combined to interpret this phenomenon. The results indicated that the source region experienced a local stratospheric intrusion and exhibited a large horizontal CO2 gradient. At the altitude where the CO concentration was lower, there was a higher CO2 concentration and vice versa. A laminar structure with multiple origins resulted in the highly negative correlation between CO2 and CO in the upper troposphere on June 14. The contribution of stratospheric airmass to the upper troposphere and that of tropospheric airmass to the lower stratosphere were 26.7% and 24.3%, respectively based on a mass balance approach. Another interesting phenomenon is that CO2 and CO levels increased substantially at approximately 8 km on June 13. Backward trajectory analyses showed that the airmass originated from a region with significant anthropogenic sources. The slope of CO2/CO representing the anthropogenic sources was 87.3 ppm/ppm. In addition, the CO2 profile showed that there was a large CO2 gradient of 4 ppm/km within the boundary layer on June 13, and this gradient disappeared on June 14.