The formation and temporal evolution of the sulphate aerosol cloud generated by the volcanic eruption of Mount Pinatubo in June 1991 is simulated using a two-dimensional sulphate aerosol model. Results are compared to times series of SO2 and aerosol data (aerosol mass, optical depth, and surface area density). The modeled SO2 decay appears to be broadly consistent with observations. The absence of homogeneous nucleation in the model seems to lead to significant discrepancies in the timing of the peak in aerosol loading and the magnitude of the surface area density. This suggests that homogenoeus nucleation plays an important role during the early stages of a volcanic eruption in determining the average size of volcanic sulphate particles and hence their residence time in the atmosphere. By including the heterogenous hydrolysis of N2O5 to HNO3, the model predicts substantial decreses in NO2 column, enhancements in ClO column and a small reduction in global O3. The modeled aerosol layer is still far from having recovered its background level 2 years after the eruption. ¿ American Geophysical Union 1994