Stratospheric aerosol measurements in the Arctic winter of 1996/1997 with the M-55 Geophysika high-altitude research aircraft

Ln-situ aerosol measurements were performed in the northern hemispheric str atosphere up to altitudes of 21 km between 13 November 1996 and 14 January 1997, inside and outside of the polar vortex during the Airborne Polar Expe riment (APE) field campaign. These are measurements of particle size distri butions with a laser optical particle counter of the FSSP-300 type operated during 9 Eights on the Russian M-55 high-altitude research aircraft Geophy sika. For specific flights, the FSSP-300 measurements are compared with bal loon-borne data (launched from Kiruna, Sweden). It was found that the strat ospheric aerosol content reached levels well below the background concentra tions measured by the NASA operated ER-2 in 1988/89 in the northern hemisph ere. During the APE campaign, no PSC particle formation was observed at Rig ht altitudes although the temperatures were below the NAT condensation poin t during one Right. The measured correlations between ozone and aerosol giv e an indication of the subsidence inside the 1996/97 polar vortex. Despite the Lower aerosol content in the winter 1996/97 compared to the 1989 backgr ound, the heterogeneous reactivity of the aerosol (as calculated from the m easured data with additional model input) is comparable. This is due to the dependency of the reactive uptake coefficients on the atmospheric water va por content. Under the described assumptions the reaction rates on the back ground aerosol are significantly smaller than for competing gas phase chlor ine activation, as can be expected For stratospheric background conditions especially inside the polar vortex.