Trends of trace gas enhancements in transported North American anthropogenic emissions (NA-anthro minus NATL) in summer. The symbols represent the means of enhancements with vertical bars showing the 95% confidence intervals. The slopes were obtained from linear regression analyses for CO(black) and O₃ (red) enhancements. Slope ranges and p values are also shown in the figure. DOI: https://doi.org/10.1525/elementa.194.f4