Regional trend analysis of surface ozone observations from monitoring in the U.S. and Canada. These results reflect the 2000–2014 changes in summer ozone [Chang et al., 2017]. The arrow direction indicates the sign and magnitude of the ozone trend according to the scale given in the inset (i.e. downward arrows are indicative of declining ozone), and the color coding shows the statistical significance of the ozone change, with statistical significant changes (at P > 95%) indicated by the bold colors. The DMA/NCFR is indicated by the red circle. This figure is a partial reproduction of Figure 1 in Chang et al. (2017). DOI: https://doi.org/10.1525/elementa.398.f6