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

The work presents measurements obtained with the multi-input spectroradiometer GASCOD/A4p, 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 measurement 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 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. 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 425 K surface confirms that low ozone air masses inside the vortex and strong sunlight greatly favour a more rapid formation of passive chlorine reservoirs.