Figure S3. Observed tracer seasonal cycles, reconstructed for three ACT regions and from five ACT campaigns shown in Figure 1. (Top Row) Observations are partitioned as atmospheric boundary layer (PBL) and free troposhere (FT) using on-board thermodynamics and lidar data. (Bottom Row) Tracer enhancements shown as difference between individual BL samples and seasonal-regional averaged FT samples (BL – \(\overline{\text{FT}}\)). Positive/negative values indicate higher/lower CO2 in the BL relative to the FT. Error bars represent the standard error across individual flask samples.