A comparison of measured and simulated ozone concentrations in the rural areas of the eastern United States during summer 1995

The recent regulatory actions toward a longer-term (i.e., 8-hr) average ozo ne standard have brought forth the potential for many rural areas in the ea stern United States to be in noncompliance. However, since a majority of th ese rural areas have generally few sources of anthropogenic emissions, the measured ozone levels primarily reflect the effects of the transport of ozo ne and its precursor pollutants and natural emissions. While photochemical grid models have been applied to urban areas to develop ozone mitigation me asures, these efforts have been limited to high ozone episode events only a nd do not adequately cover rural regions. In this study, we applied a photo chemical modeling system, RAMS/UAM-V, to the eastern United States from Jun e 1-August 31, 1995. The purpose of the study is to examine the predictive ability of the modeling system at rural monitoring stations that are part o f the Clean Air Status Trends Network (CASTNet) and the Gaseous Pollutant M onitoring Program (GPMP). The results show that the measured daily 1-hr ozo ne maxima and the seasonal average of the daily 1-hr ozone maxima are in be tter agreement with the predictions of the modeling system than those for t he daily 8-hr ozone maxima. Also, the response of the modeling system in re producing the measured range of ozone levels over the diurnal cycle is poor , suggesting the need for improvement in the treatment of the physical and chemical processes of the modeling system during the nighttime and morning hours if it is to be used to address the 8-hr ozone standard.