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 (Tmax) 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‐Tmax relationships, so we refit the ozone‐Tmax slope using logistic regression and a generalized Pareto distribution model. We then apply the resulting hybrid‐extreme value theory model to projections of Tmax 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. Key Points We use observed ozone‐temperature relationships and extreme value theory to predict future ozone An unexpected 20% of U.S. sites show ozone suppression at extremely high temperatures Results from CMIP5 imply increases in U.S. ozone episodes by as much as 3–9 days by the 2050s