The sensitivity of ozone predictions to the changes in biogenic hydrocarbon chemistry and emissions was investigated. A Lagrangian box model, the OZIPR/EKMA model, was used to examine the differences of O3 predicted using two sets of chemical mechanisms, the original CB4 mechanism and the updated CB4 mechanism with new isoprene chemistry under various emissions scenarios. In selected urban case, the updated CB4 mechanism predicted lower O3 than the original CB4 mechanism. However, in the selected rural case, the updated CB4 mechanism predicted higher O3 than the original CB4. The level of temperature selected had a significant impact to the calculation of biogenic emission rates.