The influence of the sulfate aerosol formed following the massive Pinatubo volcanic eruption in June 1991 on the chemical composition, temperature, and dynamics of the atmosphere has been investigated with the University of Illinois at Urbana-Champaign (UIUC) stratosphere--troposphere General Circulation Model (GCM) with interactive photochemistry (ST-GCM/PC). Ensembles of five runs have been performed for the unperturbed (control) and perturbed (experiment) conditions. The simulated repartitioning within the chlorine and nitrogen groups, as well as the ozone changes, are in reasonable quantitative agreement with observations and theoretical expectations. The simulated ozone changes in the tropics reveal the ozone mixing ratio decreases below 28 km and increases in the stratosphere above this level. However, these changes are not statistically significant in the lowermost stratosphere. The simulated total ozone loss reached 15% over the northern middle and high latitudes in winter and early spring. However, the simulated changes are statistically significant only during early winter. The magnitude of the simulated total ozone depletion is generally less than that observed, but some members of the experiment ensemble are in better agreement with the observed ozone anomalies. The model simulates a pronounced stratospheric warming in the tropics, which exceeds the warming derived from observations by 1--2 K. The model matches well the intensification of the polar-night jet (PNJ) in December 1991 and 1992, the statistically significant cooling of the lower stratosphere and warming of the surface air in boreal winter over the United States, northern Europe, and Russia, and the cooling over Greenland, Alaska, and Central Asia.