The time series for normalized MDA ozone is shown in

The time series for normalized MDA8 BML-190 is shown in Fig. 1A, compared to the record of Pb concentration air (Fig. 1B) and compared to the MDA8 ozone time series in Supporting Fig. S2. The average MDA8 ozone over 1992–2013 was 49.6 ppbv (± 9 ppbv), at the upper range of the North American background value calculated in models (with North American emissions turned off). Fiore et al. (2014) reported seasonal average maximum MDA8 values of 40–50 ppbv for the spring and for the summer a range of 25 to 40 ppbv based on global models (GEOs-Chem and GFDL AM3). In the GBNP data set, only 3% of dates had MDA8 ozone below 35 ppbv, while 5.5% of dates had MDA8 ozone above 65 ppbv (average of 69.7 ppbv). This illustrates the utility of observational data to verify models. Here we are providing data to test model results for the effect of long-range transport on ozone concentrations in the Intermountain West using GBNP as an exemplar.