Impact of the eruption of Mt Pinatubo on the chemical composition of the stratosphere

Abstract

This article describes the volcanic effect of the Mt Pinatubo eruption in June 1991 on the ozone (O3) and methane (CH4) distribution in the stratosphere, as simulated with the chemistry–climate model EMAC (ECHAM/MESSy Atmospheric Chemistry: ECHAM5, version 5.3.02; MESSy, version 2.51). In this study, the effects of volcanic heating and heterogeneous chemistry on the chemical composition, caused by the volcanic aerosol, are separated. Global model simulations over the relevant period of the eruption from 1989 to 1997 with EMAC in T42L90MA resolution with specified dynamics and interactive chemistry were performed. The first simulation (VOL) contains the volcanic perturbation as an additional aerosol load and thus simulates the interaction of the aerosol with the chemistry and the radiation. The second simulation (NOVOL) neglects the eruption and represents the undisturbed atmosphere. In the third simulation (CVOL) the volcanic aerosol only interacts with the heterogeneous chemistry, such that volcanic heating is omitted. The differences between the simulation results VOL−NOVOL describe the total effect of the Mt Pinatubo eruption on the chemical composition, VOL−CVOL the stratospheric heating effect, and CVOL−NOVOL the chemical effect of the aerosol on the heterogeneous chemistry. The post-volcanic stratosphere shows a decrease in the O3 column in the tropics and an increase in the midlatitudes and polar regions, lasting roughly 1 year. This change in the ozone column is solely a result of the heating effect. The subsequent decrease in the ozone column is related to the chemical effect. The contribution of the catalytic loss cycles (NOx, HOx, ClOx, and BrOx) on the depletion of O3 is analysed in detail. In the tropics, CH4 increases in the upper stratosphere because of stronger vertical transport.