Stratospheric minor gas distribution over the Antarctic Peninsula during the APE–GAIA campaign

Abstract

This work presents measurements obtained with the multi‐input spectroradiometer GASCOD/A4π, the Fourier transform far‐infrared interferometer SAFIRE‐A and the two‐channel chromatograph HAGAR, on board the M‐55 Geophysica stratospheric aircraft during the APE–GAIA campaign, held in September–October 1999 over the Antarctic Peninsula. The paper aims to investigate the gas mixing ratio distributions at the flight altitude, during a recovery phase of the reservoir species in the lower stratosphere in the Antarctic spring. Attention is focused on the daytime flight of 23 September, when the aircraft flew inside the vortex at two different altitudes (about 16.5 km and 18.5 km). Concentration distributions were examined for NO₂, N₂O, O₃, BrO, ClO, HCl, H₂O and HNO₃, during flight inside and outside the vortex. The NO₂ maxima were well defined in the edge region both on entry into and exit from the vortex at different flight altitudes. Simultaneous concentration measurements of HNO₃ and H₂O showed a denitrification but not dehydration inside the vortex core. The reformation of chlorine reservoirs is investigated. It was evident that the re‐conversion of HCl was favoured in the Cl+CH₄ branches, and its high mixing ratio up to 1 ppbv at 425K surface confirms that low ozone air masses inside the vortex and strong sunlight greatly favour a more rapid formation of passive chlorine reservoirs.

Acknowledgements

The authors wish to express their thanks to all those involved in the logistic organization and, in particular, to the Russian team for its excellent collaboration and support during the campaign. Thanks also go to the Italian Antarctic Research Program (PNRA), which supported the campaign and to all the APE team from ENEA and CNR. D. Bortoli was supported financially by the Subprograma Ciência e Tecnologia do 3° Quadro Comunitário de Apoio.