The MEGAN biogenic emission model is 3rd generation modeling system that accounts for detailed vegetation species distributions, canopy processes, and other environmental factors to simulate biogenic trace gas emissions. In this paper, results are presented as part of a comprehensive investigation of the effects of global change upon regional air quality in the U.S. The Weather Research Forecast model is applied at hemispheric (220 km grid cells) and continental US (36 km grid cells) scales for current and future decades to downscale climate effects from the A1B IPCC scenario with the ECHAM5 global model output. These results are compared to previous simulations derived from the A1 scenario with the PCM global model.