Using current biogenic emission estimates, Urban Airshed Model simulations for Atlanta, Georgia substantially underpredict isoprene concentrations relative to observations. In this work, an inverse method is used to determine the biogenic isoprene emissions for Atlanta that minimize the difference between the model-simulated and the observed isoprene concentrations. The resulting isoprene emissions are 2 to 10 times higher than any of the accepted emission estimates. Overall, the concurrent ozone simulation improved when the biogenic isoprene emissions were increased. These higher isoprene emissions significantly increase the concentration of model-simulated ozone within the plumes of nitrogen oxides emitted from large point sources. These results should be considered when developing control strategies for urban ozone.