Effects of changing power plant NO_x emissions on ozone in the eastern United States: Proof of concept

Abstract

Recent decreases in nitrogen oxide (NO x = NO + NO 2 ) emissions from eastern U.S. power plants and their effects on regional ozone are studied. Using the EPA 1999 National Emission Inventory as a reference emission data set, NO x and sulfur dioxide (SO 2 ) emission rates at selected power plants are updated to their summer 2003 levels using Continuous Emission Monitoring System (CEMS) measurements. The validity of the CEMS data is established by comparison to observations made on the NOAA WP‐3 aircraft as part of the 2004 New England Air Quality Study. The impacts of power plant NO x emission decreases on O 3 are investigated using the WRF‐Chem regional chemical forecast model. Summertime NO x emission rates decreased by approximately 50% between 1999 and 2003 at the subset of power plants studied. The impact of NO x emission reductions on ozone was moderate during summer 2004 because of relatively cool temperatures and frequent synoptic disturbances. Effects in individual plant plumes vary depending on the plant's NO x emission strength, the proximity of other NO x sources, and the availability of volatile organic compounds (VOCs) and sunlight. This study provides insight into the ozone changes that can be anticipated as power plant NO x emission reductions continue to be implemented throughout the United States.