Adjoint estimation of ozone climate penalties

An adjoint of a regional chemical transport model is used to calculate location‐specific temperature influences (climate penalties) on two policy‐relevant ozone metrics: concentrations in polluted regions (>65 ppb) and short‐term mortality in Canada and the U.S. Temperature influences through changes in chemical reaction rates, atmospheric moisture content, and biogenic emissions exhibit significant spatial variability. In particular, high‐NO x , polluted regions are prominently distinguished by substantial climate penalties (up to 6.2 ppb/K in major urban areas) as a result of large temperature influences through increased biogenic emissions and nonnegative water vapor sensitivities. Temperature influences on ozone mortality, when integrated across the domain, result in 369 excess deaths/K in Canada and the U.S. over a summer season—an impact comparable to a 5% change in anthropogenic NO x emissions. As such, we suggest that NO x control can be also regarded as a climate change adaptation strategy with regard to ozone air quality.