An operational evaluation of two regional-scale ozone air quality modelingsystems over the eastern United States

In this paper, the performance of two commonly used regional-scale Eulerian photochemical modeling systems, namely, RAMS/UAM-V and MM5/SAQM, from the regulatory or operational perspective, is examined. While the Urban Airshed Model with Variable Grid (UAM-V) is driven with the meteorological fields derived from the Regional Atmospheric Model System (RAMS), the San Joaquin Valley Air Quality Model (SAQM) used the meteorological fields derived from the Pennsylvania State University-National Center for Atmospheric Research Mesoscale Model Version 5 (MM5). The model's performance in reproducing th e observed ozone air quality over the eastern United States is evaluated fo r three typical high-ozone episodic events that occurred during 16-20 June, 12-16 July, and 30 July-2 August of 1995. The prevailing meteorological co nditions associated with these three episodes are characterized by a slow e astward-moving high pressure system, westerly and southwesterly low-level j ets, stable boundary layers, and the Appalachian lee-side trough. The resul ts suggest that the performance of RAMS/UAM-V and MM5/SAQM systems in repro ducing the observed ozone concentrations is comparable when model outputs a re averaged over all simulated days. For different emissions reduction (i.e ., volatile organic compound and nitrogen oxide controls) options, the resp onse of both modeling systems, in terms of changes in ozone levels, was dir ectionally similar, but the magnitude of ozone improvement differed fi om i ndividual episode days at individual grid cells.