Interpreting Regional Carbon Enhancements During the ACT-America Campaign Using Multi-Species Flask Measurements

Although global-scale carbon budgets are well known, regional-scale budgets have higher uncertainties, complicating greenhouse gas mitigation efforts. Two of the goals of the Atmospheric Carbon and Transport-America (ACT-America) study are to: a) reduce regional atmospheric model transport uncertainty and b) improve regional-scale estimates of carbon dioxide (CO­2) and methane (CH4) fluxes. ACT-America airborne flask measurements of these greenhouse gases, carbon monoxide (CO), and other hydrocarbon tracers for anthropogenic and biogenic processes can lend insight into atmospheric composition, helping to improve our understanding of regional to continental scale carbon enhancements. The ACT-America campaign specifically investigates the role of synoptic-scale transport on the variability of observed CO2 and CH4. Continuous in situ measurements of CO2 and CH4 show large gradients at frontal boundaries. We examine how relationships between observed enhancements in CO2, CH4, and other tracer species above background levels can lend insight into the sources and sinks creating these gradients. Strong correlations between CO2 and CH4 during the ACT-America winter 2017 campaign suggest that co-located sources exist between these two species; supporting isotopic flask measurements of Δ13CH4 and Δ14CO2 can provide important constraints on the sources of these enhancements. We examine the extent to which relationships between carbon and trace gas species can explain observed regional-scale CO2 and CH4 enhancements above background levels across the eastern United States in an effort to improve our understanding of regional carbon fluxes and more accurately represent these fluxes in current modeling frameworks.