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Frequency distributions of NOx (pptv, left) and O3 (ppbv, right) derived from NOXAR measurements (top) and E39/C model data (bottom). Data are analysed in a region of 50 hPa below the local tropopause. NOXAR consists of a year of measurements made on board regular passenger aircraft flying between Europe and Eastern USA and Europe and the Far East (adapted from Grewe et al., 2001).
