The tightening of proposed EPA ozone National Ambient Air Quality Standards (NAAQS) will significantly affect National Parks. In this study, CAMx (the Comprehensive Air Quality Model with Extensions) was used to simulate surface ozone concentrations at western US parks, with the aim of providing additional information as to which Parks are most likely to violate the new standards. Although ozone is measured at several National Parks as part of the NPS Gaseous Pollutant Monitoring Program (GPMP) and EPA's Clean Air Status and Trends Network (CASTNet), many parks have no air quality measurements and have instead relied upon interpolated observations to indicate their respective ozone levels. Given the complexity and heterogeneity of ozone concentrations, these interpolated estimates may be missing important signatures of ozone transport and formation. CAMx simulations were based on the 12km 2005 Four Corners Air Quality Task Force study.