To improve air quality forecasting, an ensemble is created by varying the physics options of a mesoscale meteorology model, WRF-ARW. The meteorology ensemble is produced by changing settings to three key physics options for air quality applications: the planetary boundary layer (PBL) module, shortwave (SW) radiation parameterization, and cumulus cloud simulation. Two options each for SW radiation, PBL and cumulus have been chosen to create the eight-member ensemble. Although the surface layer (SL) options are technically separate from the PBL modules, in practice they must be changed in tandem. The longwave (LW) radiation module will also be changed to complement the SW option. These meteorology members are processed MCIP and input to SMOKE. The meteorology ensemble members and their corresponding emission members are used as input for CMAQ, resulting in an eight-member ozone forecast ensemble. This project analyzes the impact of specific PBL/SL, SW/LW radiation, and cumulus parameterizations on emissions, chemistry, and transport to separate out the effects of each. This poster will show the preliminary results of this study on Summer 2006 in the middle East Coast of the United States. It will focus on August 1-4, during which CMAQ forecasts overpredicted ozone concentrations in this area.