Impact of Climate Variability and Change on the Surface Ozone Response to NO_x Emissions Reductions

Climate variability and change introduce a range of air quality outcomes for a given emissions policy. Quantifying this range helps us evaluate the likelihood of meeting air quality targets in an uncertain future climate. Using a global atmospheric chemistry model ensemble, we project how the ozone response to a 10% reduction in anthropogenic nitrogen oxides (NO_x) emissions varies across three northern midlatitude source regions under two future climate scenarios. In Eastern North America and West-Central Europe, where ambient ozone is NO_x-sensitive in the historical scenario, the magnitude of ozone reductions from reduced NO_x is smaller under high warming relative to that under the historical scenario because of the dominant effect of increased soil NO_x emissions. In North East Asia, where ambient ozone is NO_x-insensitive in some areas in the historical scenario, the magnitude of ozone reductions from reduced NO_x increases under high warming due to the dominant effect of enhanced HO_x production. In North East Asia, these changes lead to a significant decrease in the frequency of days with ozone disbenefits from NO_x reductions under the high-warming scenario relative to the historical scenario, while no statistically significant increase in ozone disbenefits is found for Eastern North America or West-Central Europe.