The EPA’s recent release of ozone air quality designations augmented its previous designation of areas that are in nonattainment for EPA’s 2015 ozone NAAQS standards.1 The air quality improvements needed in these nonattainment areas highlight the role that existing nuclear power plants play in air quality. Simply put, nuclear plants avoid air pollutants associated with fossil generation. The loss of nuclear generation increases emissions as fossil generators operate more to fill the gap. We identified and quantified this effect in several previous studies that examined the environmental impacts of nuclear plants in Ohio, Illinois, New Jersey and Pennsylvania. These studies showed that the loss of zero-emission nuclear generation would result in increased fossil generation and thus increased emissions of several pollutants, including NOX, which is both a pollutant in its own right and a precursor for ozone. Some of the NOX increases would occur within ozone nonattainment areas, just when states must develop plans to decrease pollutant concentrations in those areas. The loss of nuclear plants would increase the challenge and the cost of bringing nonattainment areas into compliance with air quality standards.