POLAR OZONE DEPLETION - A 3-DIMENSIONAL CHEMICAL MODELING STUDY OF ITS LONG-TERM GLOBAL IMPACT

The export of ozone-poor air from the polar region following the break up of the southern hemisphere polar vortex is examined with a three-di mensional chemistry transport model. This volume of depleted ozone, th e result of-chemical processing during the southern wintertime and spr ingtime, is long-lived in the lower stratosphere and can affect ozone concentrations at southern middle latitudes following its transport ou t of the polar region. Two 5-year simulations were performed utilizing the NASA Langley Research Center three-dimensional chemistry transpor t model. One simulation included only gas phase and sulfate aerosol ch emistry, while the second simulation also included reactions occurring on polar stratospheric clouds (PSCs). The model-calculated seasonal v ariation of southern hemispheric O-3, HNO3, and active chlorine as a r esult of PSC chemistry is in reasonable accord with satellite observat ions. The model reveals that ozone is transported equatorward followin g the breakup of the polar vortex to approximately 20 degrees S latitu de by the first southern summer following the activation of PSC chemis try. A residual column-integrated ozone depletion of 9% remained by th e springtime of the second year, In subsequent years, the southern ozo ne hole itself increased in depth from a column-integrated depletion o f 37% in the first year to 43% in the fifth year with respect to the b aseline simulation with no PSC chemistry. The isopleths of column-inte grated ozone loss showed a slow equatorward movement during the 5-year run. These model results, in general agreement with earlier model stu dies using parameterized chemistry, show that a potential exists for a long-term accumulation of ozone loss in the southern polar region and a gradual increase in the global impact of polar ozone depletion. Com parison with satellite and ground-based observations of ozone trends a t midlatitudes suggests that ozone dilution may be a contributing fact or. Experiments were performed to examine the sensitivity of the rate of local ozone recovery following the breakup of the vortex to the dep th and spatial extent of the denitrification of polar air, These simul ations revealed that deeper denitrification led to a more persistent c olumn-integrated ozone loss and a slight increase in its equatorward p rogression.