An Estimate of the Chemical and Radiative Perturbation of Stratospheric Ozone Following the Eruption of Mt. Pinatubo

In this work a numerical assessment is attempted of trace species interactions with aerosols injected in the stratosphere by the eruption of Mt. Pinatubo. A photochemical two-dimensional model is used for this purpose, with heterogeneous chemical conversion of odd nitrogen into nitric acid taken as the basic perturbation on nitrogen, chlorine, and ozone. In addition, it is shown that the radiative perturbation induced by the aerosols is an important depletion mechanism for ozone at least at tropical latitudes where the optical thickness of volcanic particles has remained sufficiently high for several months after the eruption. The radiative interaction with stratospheric trace species not only takes place through changes in photodissociation frequency but is also a consequence of solar and planetary radiation absorption by the aerosol particles. The resulting heating rates produce a nonnegligible equatorial upwelling whose effects on dynamics and transport have been studied using a three-dimensional model. They are presented here, along with photochemical calculations, in order to assess the different contributions to the ozone depletion after the eruption. The magnitude of the radiative perturbation is found to be comparable to that of heterogeneous chemistry except at the northern midlatitudes during winter and spring where the chemical perturbation dominates. In addition, the radiative perturbation is found to be largely determined by photolysis in the tropics, while the effects on circulation are most significant at high latitudes. The total radiative effect on the ozone column is that of an ∼5% depletion in the tropics along with a wintertime increase poleward of 50° latitude (about 4%–6% in the Northern Hemisphere). Both magnitude and features of the ozone depletion resulting from this numerical calculation are successfully compared to recent observations taken at tropical latitudes during 1991.