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Frontal boundaries have been shown to cause large changes in CO2mole‐fractions, but clouds and the complex vertical structure of fronts make these gradients difficult to observe. It remains unclear how the column average CO2dry air mole‐fraction (XCO2) changes spatially across fronts, and how well airborne lidar observations, data assimilation systems, and numerical models without assimilation capture XCO2frontal contrasts (ΔXCO2,i.e., warm minus cold sector average of XCO2). We demonstrated the potential of airborne Multifunctional Fiber Laser Lidar (MFLL) measurements in heterogeneous weather conditions (i.e., frontal environment) to investigate the ΔXCO2during four seasonal field campaigns of the Atmospheric Carbon and Transport‐America (ACT‐America) mission. Most frontal cases in summer (winter) reveal higher (lower) XCO2in the warm (cold) sector than in the cold (warm) sector. During the transitional seasons (spring and fall), no clear signal in ΔXCO2was observed. Intercomparison among the MFLL, assimilated fields from NASA's Global Modeling and Assimilation Office (GMAO), and simulations from the Weather Research and Forecasting‐—Chemistry (WRF‐Chem) showed that (a) all products had a similar sign of ΔXCO2though with different levels of agreement in ΔXCO2magnitudes among seasons; (b) ΔXCO2in summer decreases with altitude; and (c) significant challenges remain in observing and simulating XCO2frontal contrasts. A linear regression analyses between ΔXCO2for MFLL versus GMAO, and MFLL versus WRF‐Chem for summer‐2016 cases yielded a correlation coefficient of 0.95 and 0.88, respectively. The reported ΔXCO2variability among four seasons provide guidance to the spatial structures of XCO2transport errors in models and satellite measurements of XCO2in synoptically‐active weather systems. First airborne observations of column average CO2dry‐air mole‐fraction (XCO2) changes across fronts observed during ACT‐A are reportedXCO2frontal structures compare reasonably well with Weather Research and Forecasting—Chemistry and an in situ data driven assimilation systemResults reveal that the differences across models and data were generally much smaller than the magnitude of XCO2frontal contrasts First airborne observations of column average CO2dry‐air mole‐fraction (XCO2) changes across fronts observed during ACT‐A are reported XCO2frontal structures compare reasonably well with Weather Research and Forecasting—Chemistry and an in situ data driven assimilation system Results reveal that the differences across models and data were generally much smaller than the magnitude of XCO2frontal contrasts