Chemistry and Temperature Perturbations Due to Pinatubo Aerosols Calculated by a Chemical-radiative Coupled 1-D Model.

Abstract

The increase of stratospheric aerosol caused by the Mt. Pinatubo eruption, and its effects on atmospheric temperature and chemical constituents, are studied by using a chemical-radiative coupled 1-D model. The optical parameters of the aerosols and the surface area are calculated, assuming the size distribution of the aerosols and the composition. Two kinds of numerical experiments were made in this study. In the first experiment, a simple form of vertical distribution and the time variation of the aerosols are assumed based on lidar measurement data, and satellite data analyses. The simplification is necessary for an easy and clear understanding of chemistry-radiation coupled variations in temperature and ozone. In the second experiment, lidar data are used for calculation and input into the model as a function of altitude and time. These experiments show that the temperature increased in the range of 4.7-5.8 K and the ozone concentration decreased by 13-14% at the maximum perturbation phase in the center of the aerosol layer at 20 km. The maximum total ozone decrease was 18-20 DU (5.0-5.5%). The total ozone decrease, however, was 13-15 DU (3.5-4.0%) when the effect of the temperature variation on chemistry was ignored. Sedimentation of the aerosols within the first 1-2 years after the Pinatubo eruption explains the small difference in the results of these two experiments. The experiments also show that the ground surface temperature rapidly dropped by 0.1 K-0.35 K in the first 6 months, depending on the solar radiation absorption efficiency of the aerosols, followed by a recovery of more than a half in magnitude in the next 6 months. A cooling of less than 0.1 K then continued for the next 3-4 years, until the stratospheric ozone loss disappeared. The mechanisms of this surface temperature variation in the 1-D model are studied examining the results of the first experiment. The effects of a hydrolysis reaction of BrONO2 on ozone loss are also examined. The results suggest that the hydrolysis reaction more than doubled the ozone loss. All these results from the 1-D model show substantially larger positive temperature perturbations, and a somewhat longer duration of chemical perturbations than observed.