Historical measurements of surface ozone in the Northern Temperate region, 30°N–60°N (30 European, three Asian, one North American and one North African data sets; see Table 4 for details). Error bars represent standard deviations of the measurement averages (atmospheric variability), not uncertainty of the measurement. 5-year averages of modern UV measurements at sites below 2000 m, classified as “rural”, in the 5 × 5 degree gridded product from the TOAR database are also shown, both daytime averages (day) and daily 8-hour maxima (DMA8) (Schultz et al., 2017). DOI: https://doi.org/10.1525/elementa.376.f2