OZONE RESPONSE TO ENHANCED HETEROGENEOUS PROCESSING AFTER THE ERUPTION OF MT-PINATUBO

Increases in aerosol loading after the Pinatubo eruption are expected to cause additional ozone depletion. Even though aerosol loadings were highest in the winter of 1991-1992, recent analyses of satellite and ground-based ozone measurements indicate that ozone levels in the wint er of 1992-1993 are the lowest recorded in recent years, raising the q uestion of the mechanisms responsible for such behavior. We have incor porated aerosol surface areas derived from the Stratospheric Aerosol a nd Gas Experiment II (SAGE-II) measurements into our two-dimensional m odel. Inclusion of heterogeneous chemistry on these enhanced aerosol s urfaces yields maximum ozone reductions during the winter of 1992-1993 in the Northern Hemisphere, consistent with those derived from observ ations. This delayed behavior is due to the combination of the non-lin ear nature of the impact of heterogeneous reactions as a function of a erosol surface area, and the long time constants for ozone in the lowe r stratosphere. If heterogeneous mechanisms are primarily responsible for the low 1992-1993 ozone levels, we expect ozone concentrations to start recovering in 1994.