Maintenance of high HCl/Cl-y and NOx/NOy in the Antarctic vortex: A chemical signature of confinement during spring

Observations made in the 1994 Antarctic vortex show that Cl-y recovered com pletely into HCl following conversion of Cl-y reservoir species to active r adicals, and NOx constituted a 4-5 times higher fraction of NOy inside the vortex than outside. Measurements made in October and November from the Air borne Southern Hemisphere Ozone Expedition/Measurements of the Atmospheric Effects of Stratospheric Aircraft (ASHOE/MAESA) ER-2 aircraft mission, the third Atmospheric Laboratory for Applications and Science (ATLAS-3) space s huttle mission, and the Upper Atmosphere Research Satellite (UARS) demonstr ate that this unusual partitioning of Cl-y and NOy was maintained for at le ast 4 weeks in the springtime vortex. In response to severe ozone loss, abu ndances of HCl and NOx remained high despite temperatures low enough to rea ctivate Cl-y and convert NOx to HNO3 via heterogeneous processes. Thus, und er severely ozone depleted conditions, high HCl and NOx abundances in the v ortex are maintained until the vortex breaks up or an influx of ozone-rich extravortex air is entrained into the vortex. These observations suggest th at the flux of extravortex air entering the core of the lower stratospheric vortex was small or negligible above similar to 400 K during late spring, despite weakening of the vortex during this time period. Results of a photo chemical model constrained by the measurements suggest that extravortex air entrained into the vortex during October and early November made up less t han 5% of the vortex core air at 409 K. The model results also show that he terogeneous chemistry has little effect on the Cl-y and NOy partitioning on ce high abundances of HCl have been attained under ozone depleted condition s, even when aerosol loading is high.