Relaxing Energy Policies Coupled with Climate Change Will Significantly Undermine Efforts to Attain US Ozone Standards

Summary The United States (US) federal administration is relaxing energy policies (EPs), with yet uncharacterized effects on ambient air quality. The complex effects of EPs coupled with uncertainties associated with future climate have hindered past quantification. Here, we integrate model simulations to show that compared with a scenario of continued EPs and stationary climate, relaxation of EPs coupled with intense warming will increase the number of US counties in ozone nonattainment (NNA) by >75% in 2050. The NNA under the current standard of 0.070 parts per million (ppm) is projected to increase in 2050 from 27 to 49, while NNA under a tighter standard of 0.060 ppm will increase from 497 to 879. Our study demonstrates synergistic effects of EP relaxation with climate change on ozone standard compliance and indicates that the current decline in ambient ozone could be reversed by relaxing EPs in a changing climate.