Downscaling is particularly important in assessing the potential effects of global climate change on regional air quality because air quality is affected by meteorological processes at small spatial and temporal scales. In this study, a regional climate model based on the Penn State/NCAR Mesoscale Model MM5 was used to downscale the NASA Goddard Institute for Space Studies (GISS) global climate simulations of the current (1995-2005) and future (2045-2055) climate conditions for the continental U.S. Simulation of the future climate followed the IPCC SRES A1B scenario for greenhouse gas and aerosol emissions. The regional simulations were performed at 36 km spatial resolution for the U.S. Model outputs were archived at an hourly interval three-dimensionally for inputs to air quality models. Analysis of the downscaled control and future climate showed significant changes over the western U.S. during summer and fall with a warming of 2-4 degree C and reduced rainfall. Consistent with the warmer and dryer climate, there is an increase in downward solar radiation and boundary layer depth and reduced ventilation that may increase the likelihood of air pollution episodes. In contrast, changes in the Midwest and Southeastern U.S. during summer are less favorable for air pollution events. More analyses are being performed to evaluate the meteorological conditions of the control run that are important for air quality assessment and to examine the change in mean and interannual variability of those conditions. For comparison, downscaling is also being performed based on the control (1975-1995) and future (1995-2050) global climate simulated by the NCAR/DOE Parallel Climate Model (PCM). Analyses will be performed to highlight the uncertainty that arises from the use of different global climate models.