PNNL

Abstract

Ozone production efficiency (OPE) can be defined as the number of ozone (O3) molecules photochemically produced by a molecule of nitrogen oxides (NOx = NO + NO2) before it is lost from the NOx ? O3 cycle. Here, we consider observational and modeling techniques to evaluate various operational definitions of OPEs using aircraft and surface measurements taken as part of the 1999 Southern Oxidant Study field campaign in Nashville, Tennessee. A key tool in our analysis is a Lagrangian box-model, which is used to quantitatively describe the effects of emissions, dilution, dry deposition and photochemistry in the Nashville urban plume as it was advected downwind. After evaluating the model using the observed downwind concentrations of O3 and other key species, including NOx, NOy, and important VOCs, we show that the modeled NOx oxidation and O3 production rates as well as the associated cumulative and instantaneous OPEs depend on the time of day and the photochemical age of the air mass. The modeled OPEs were consistent with the observation-based values with the expected biases. Results from a model sensitivity study suggest that downwind O3 concentrations in the Nashville urban plume are more sensitive to NOx emissions than anthropogenic VOC emissions.