AEROSOL-ASSOCIATED CHANGES IN TROPICAL STRATOSPHERIC OZONE FOLLOWING THE ERUPTION OF MOUNT-PINATUBO

The large amount of sulfuric acid aerosol formed in the stratosphere by conversion of sulfur dioxide emitted by the eruption of Mount Pinatubo (15.14-degrees-N, 120.35-degrees-E) in the Philippines around June 15, 1991, has had a pronounced effect on lower stratospheric ozone in the tropics. Measurements of stratospheric ozone in the tropics using electrochemical concentration cell (ECC) sondes before and after the eruption and the airborne UV differential absorption lidar (DIAL) system after the eruption are compared with Stratospheric Aerosol and Gas Experiment II (SAGE II) measurements from several years before the eruption and ECC sonde measurements from the year prior to the eruption to determine the resulting changes. Ozone decreases of up to 33% compared with SAGE II climatological values were found to be directly correlated with altitude regions of enhanced aerosol loading in the 16- to 28-km range. A maximum partial-column decrease of 29 +/- 9 Dobson units (DU) was found over the 16- to 28-km range in September 1991 along with small increases (to 5.9 +/- 2 DU) from 28 to 31.5 km. A large decrease of ozone was also found at 4-degrees to 8-degrees-S from May to August 1992, with a maximum decrease of 33 +/- 7 DU found above Brazzaville in July. Aerosol data from the visible channel of the advanced very high resolution radiometer (AVHRR) and the visible wavelength of the UV DIAL system were used to examine the relationship between aerosol (surface area) densities and ozone changes. The tropical stratospheric ozone changes we observed in 1991 and 1992 are likely be explained by a combination of dynamical (vertical transport) perturbations, radiative perturbations on ozone photochemistry, and heterogeneous chemistry.