Polar ozone depletion: A three-dimensional chemical modeling study of its long-term global impact

The export of ozone-poor air from the polar region following the breakup of the southern hemisphere polar vortex is examined with a three-dimensional chemistry transport model. This volume of depleted ozone, the result of-chemical processing during the southern wintertime and springtime, is long-lived in the lower stratosphere and can affect ozone concentrations at southern middle latitudes following its transport out of the polar region. Two 5-year simulations were performed utilizing the NASA Langley Research Center three-dimensional chemistry transport model. One simulation included only gas phase and sulfate aerosol chemistry, while the second simulation also included reactions occurring on polar stratospheric clouds (PSCs). The model-calculated seasonal variation of southern hemispheric O-3, HNO3, and active chlorine as a result of PSC chemistry is in reasonable accord with satellite observations. The model reveals that ozone is transported equatorward following the breakup of the polar vortex to approximately 20 degrees S latitude by the first southern summer following the activation of PSC chemistry. A residual column-integrated ozone depletion of 9% remained by the springtime of the second year, In subsequent years, the southern ozone hole itself increased in depth from a column-integrated depletion of 37% in the first year to 43% in the fifth year with respect to the baseline simulation with no PSC chemistry. The isopleths of column-integrated ozone loss showed a slow equatorward movement during the 5-year run. These model results, in general agreement with earlier model studies 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. Comparison with satellite and ground-based observations of ozone trends at midlatitudes suggests that ozone dilution may be a contributing factor. Experiments were performed to examine the sensitivity of the rate of local ozone recovery following the breakup of the vortex to the depth and spatial extent of the denitrification of polar air, These simulations revealed that deeper denitrification led to a more persistent column-integrated ozone loss and a slight increase in its equatorward progression.