Impact of increasing heat waves on U.S. ozone episodes in the 2050s: Results from a multimodel analysis using extreme value theory

We develop a statistical model using extreme value theory to estimate the 2000–2050 changes in ozone episodes across the United States. We model the relationships between daily maximum temperature ( T max ) and maximum daily 8 h average (MDA8) ozone in May–September over 2003–2012 using a Point Process (PP) model. At ~20% of the sites, a marked decrease in the ozone‐temperature slope occurs at high temperatures, defined as ozone suppression. The PP model sometimes fails to capture ozone‐ T max relationships, so we refit the ozone‐ T max slope using logistic regression and a generalized Pareto distribution model. We then apply the resulting hybrid‐extreme value theory model to projections of T max from an ensemble of downscaled climate models. Assuming constant anthropogenic emissions at the present level, we find an average increase of 2.3 d a −1 in ozone episodes (>75 ppbv) across the United States by the 2050s, with a change of +3–9 d a −1 at many sites.