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Gopal Sistla, Winston Hao, Jia-Yeong Ku, George Kallos, Kesu Zhang, Huiting Mao, and S. Trivikrama Rao

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 the observed ozone air quality over the eastern United States is evaluated for 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 conditions associated with these three episodes are characterized by a slow eastward-moving high pressure system, westerly and southwesterly low-level jets, stable boundary layers, and the Appalachian lee-side trough. The results suggest that the performance of RAMS/UAM-V and MM5/SAQM systems in reproducing the observed ozone concentrations is comparable when model outputs are averaged over all simulated days. For different emissions reduction (i.e., volatile organic compound and nitrogen oxide controls) options, the response of both modeling systems, in terms of changes in ozone levels, was directionally similar, but the magnitude of ozone improvement differed from individual episode days at individual grid cells.

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