Assessing Model Characterization of Single Source Secondary Pollutant Impacts Using 2013 SENEX Field Study Measurements.

Aircraft measurements made downwind from specific coal fired power plants during the 2013 Southeast Nexus field campaign provide a unique opportunity to evaluate single source photochemical model predictions of both O and secondary PM species. The model did well at predicting downwind plume placement. The model shows similar patterns of an increasing fraction of PM sulfate ion to the sum of SO and PM sulfate ion by distance from the source compared with ambient based estimates. The model was less consistent in capturing downwind ambient based trends in conversion of NO to NO from these sources. Source sensitivity approaches capture near-source O titration by fresh NO emissions, in particular subgrid plume treatment. However, capturing this near-source chemical feature did not translate into better downwind peak estimates of single source O impacts. The model estimated O production from these sources but often was lower than ambient based source production. The downwind transect ambient measurements, in particular secondary PM and O, have some level of contribution from other sources which makes direct comparison with model source contribution challenging. Model source attribution results suggest contribution to secondary pollutants from multiple sources even where primary pollutants indicate the presence of a single source.