The evolution of chemical species during the life cycle of a severe local storm has been simulated using our three‐dimensional cloud chemistry model (Wang and Chang, 1993a, b). The importance of dynamical transport was found to be different for different gases, depending on their solubility. For insoluble gases with a comparatively long chemical lifetime, dynamical transport was a major factor in the evolution of in‐cloud gas phase concentration. The three‐dimensional divergence (convergence) and eddy mixing accounted for nearly 100% of the total variation of the in‐cloud O3 amount. For the highly soluble gases such as HNO3 and H2O2 the dominant sources and sinks were dissolution and evaporation. The dissolution of HNO3 and H2O2 accounted for more than 44% of the total change. The extensive condensation occurring in selected parts of the storm caused sharp decreases in the HNO3 and H2O2 mixing ratios. The dissolution of SO2 can exceed the influence of dynamical processes for a short time period, corresponding to a newly born convective cell. For other times, dynamics was the major factor influencing the variation of the SO2 in‐cloud amount. The in‐cloud amounts of the gas phase pollutants were reduced significantly during the development of the storm. The net decrease of SO2 is approximately equal to 4 ppt on the average throughout the entire cloud volume during the simulation, or approximately −3 ppt/h in rate. For O3 the total change is approximately equal to −1.1 ppb/h on the average. The net decrease of HNO3 is equal to 20 ppt on the average, or −15 ppt/h in rate. The H2O2 decreasing rate is approximately equal to −5.9 ppb/h on the average, while the average net change is about 7.8 ppb in the cloud volume and averaged through the duration of the simulation.