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

Observations made in the 1994 Antarctic vortex show that Cly recovered completelyinto HC1 following conversion ofCly reservoir species to active radicals, and NOx constituted a4-5 times higher fraction of NOy inside the vortex than outside. Measurements made in Octoberand November from the Airborne Southern Hemisphere Ozone Expedition/Measurements of theAtmospheric Effects of Stratospheric Aircraft (ASHOE/MAESA) ER-2 aircraft mission, the thirdAtmospheric Laboratory for Applications and Science (ATLAS-3) space shuffle mission, and theUpper Atmosphere Research Satellite (UARS) demonstrate that this unusual partitioning ofClyand NOy was maintained for at least 4 weeks in the springtime vortex. In response tosevere ozoneloss, abundances of HC1 and NOx remained high despite temperatures low enough to reactivate Clyand convert NOx to HNO3 via heterogeneous processes. Thus, under severely ozone depletedconditions, high HC1 and NOx abundances in the vortex are maintained until the vortex breaks upor an influx of ozone-rich extravortex air is entrained into the vortex. These observations suggestthat the flux of extravortex air entering the core of the lower stratospheric vortex was small ornegligible above -400 K during late spring, despite weakening of the vortex during this timeperiod. Results of a photochemical model constrained by the measurements suggest that extravortex air entrained into the vortex during October and early November made up less than 5% ofthe vortex core air at 409 K. The model results also show that heterogeneous chemistry has littleeffect on the Cly and NOy partitioning once high abundances of HC1 have been attained under ozonedepleted conditions, even when aerosol loading is high.