Estimating potential productivity cobenefits for crops and trees from reduced ozone with U.S. coal power plant carbon standards

A standard for carbon dioxide emissions from power plants in the United States, known as the Clean Power Plan, has been finalized by the Environmental Protection Agency. Decreases in carbon dioxide emissions from fossil fuel combustion have the potential cobenefit of reductions in emissions of oxides of nitrogen, which contribute to the formation of ground-level ozone. Emissions of ozone precursors may result in elevated ozone concentrations nearby or downwind. Chronic exposure of sensitive vegetation to tropospheric ozone reduces its potential productivity. To evaluate the cobenefits of the Clean Power Plan to sensitive vegetation, we estimate ozone concentrations in the continental U.S. in 2020 with a chemical transport model in accordance with reference and alternative Clean Power Plan policy scenarios, which represent a range of possible approaches to reducing carbon dioxide emissions from power plants. The reductions in biomass, or the potential productivity losses, due to the exposure of 4 crops and 11 tree species to ozone are as large as 1.9% and 32%, respectively, in the reference scenario. The least stringent policy scenario reduces these losses by less than 3% for any given species; however, the scenarios consistent with policies resulting in more rigorous nitrogen oxide reductions produce potential productivity losses lower than the reference scenario by as much as 16% and 13% for individual crops or tree species, respectively. This analysis affords the opportunity to consider public welfare cobenefits of a regulation that is designed to reduce carbon dioxide emissions from power plants.