A STUDY OF GROUND-LEVEL OZONE OVER THE BALTIMORE/WASHINGTON OZONE NONATTAINMENT AREA

Abstract

Surface ozone is a persistent problem in U.S.A. and Europe as well as developing countries. A key prerequisite to identifying effective approaches to meeting an ozone air quality standard is to understand the relationship between VOC and NOx, the significance of biogenic emissions, and the contribution of long-range transport.

The Baltimore/Washington area is an EPA-designated severe ozone non-attainment area. In this study, the characteristics of ozone events over this area were investigated to develop a possible control strategy. Both observational and computational modeling approaches were employed, and it was divided into three parts. The first part was to investigate sources of VOC emissions in the Baltimore area using highly time resolved measurements, and to investigate possible relationships between each VOC source category and episodes of elevated ozone concentrations. The results showed that biogenic emissions contribute significantly to local ozone production in this area. The second part was emissions inventory evaluation, focused on VOC emissions inventory because VOC estimates are commonly assumed to be more uncertain than NOx estimates. The results indicated a possibility of overestimation of solvent VOC emissions. Photochemical simulations with reduction of solvent VOC emissions did not affect ozone prediction, but affected significantly secondary organic aerosol prediction. Lastly, photochemical ozone simulations were performed to find an effective control strategy for this area. The simulation results showed that long-range transport of ozone was responsible for 20-90 ppb of ozone concentration in the state of Maryland, Northern Virginia, and D.C. area, displaying a decreasing contribution as it approached to the Baltimore/Washington area. Local emissions contributed considerably to high ozone occurrences in this area. Moreover, the contribution of biogenic VOC emissions in this region was responsible for much of the local ozone production, which was a consistent result from the part one. Accordingly, the results indicated that NOx emissions reductions would probably mitigate high ozone occurrences in this area, and this was confirmed through several simulations with emissions reductions. However, our results suggested that control of only local NOx emissions might not be sufficient to comply with the 8 hr ozone standard because of the importance of long-range transported ozone.