Under the Clean Smokestacks Act enacted by North Carolina’s General Assembly in 2002, emissions of nitrogen oxides (NOx) and sulfur dioxide (SO2) from coal-fired power plants in North Carolina will be reduced. The act recognized that sources outside North Carolina also contribute to North Carolina’s air pollution and directed the North Carolina Department of Justice (NCDOJ) to seek similar reductions in nearby states. As a result, the NCDOJ initiated legal action to obtain additional emissions reductions at power plants operated by the Tennessee Valley Authority (TVA). STI staff members served as expert witnesses in NCDOJ’s litigation by performing a set of analyses to characterize and quantify the air quality benefits of additional controls. These analyses included characterization of air quality and pollutant transport in the region, annual photochemical modeling with the Community Multiscale Air Quality (CMAQ) model to quantify the benefits of emission reductions, and the production of a movie to illustrate, in three dimensions, the emission, chemical transformation, and transport of pollutants. The results of these analyses were presented in three expert reports and in trial testimony in U.S. District Court. The Court held that four TVA coal-fired power plants nearest North Carolina are causing a public nuisance in North Carolina and ordered TVA to install additional air pollution controls on those plants.