A 3-DIMENSIONAL MODEL SIMULATION OF THE IMPACT OF MT. PINATUBO AEROSOL ON THE ANTARCTIC OZONE HOLE

Seasonal integrations of a three-dimensional fully coupled model of th e radiation, dynamics and chemistry of the stratosphere and mesosphere are presented for the southern hemisphere spring. Included in the mod el are heterogeneous reactions which take place in sulphuric acid aero sol droplets as well as on the surface of Polar Stratospheric Clouds ( PSCs). Calculations are performed for background levels of stratospher ic aerosol and for conditions following the eruption of Mt. Pinatubo. For the volcanic case, surface area densities are derived from Improve d Stratospheric and Mesospheric Sounder data. For background aerosol l oadings there are significant increases in HOx and ClOx, as well as re ductions in NOx. These effects are enhanced following the Pinatubo eru ption but saturate at relatively low aerosol levels and hence can pers ist in the stratosphere for several years. Where PSCs are predicted to form, the sulphate aerosol chemistry does not operate in the model si nce the aerosols are incorporated as nuclei within the PSCs. In contra st, on the edge of the ozone hole, where temperatures are only just to o high for the formation of PSCs, destruction by aerosol can result in further total ozone depletion of order 20 Dobson Units. Tn addition, the size and duration of the ozone hole are both increased by the pres ence of volcanic aerosols. The results support previous suggestions th at the eruption of Mt. Pinatubo resulted in a temporary increase in oz one depletion over Antarctica and elsewhere.