OBSERVATIONS OF NITRIC-ACID PERTURBATIONS IN THE WINTER ARCTIC STRATOSPHERE - EVIDENCE FOR PSC SEDIMENTATION

Gaseous nitric acid (HNO3) and hydrogene fluoride CHF) have been measu red in the winter Arctic stratosphere using balloon- and aircraft-base d Ion Molecule Reaction Mass Spectrometry (IMRMS) instruments. Strong HNO3 perturbations were found in 1993 and 1995 which may indicate nitr ification around 11-13 km and denitrification around 20 km altitude. M ost likely these perturbations were caused by sedimentation of HNO3 co ntaining aerosols followed by aerosol evaporation at lower altitudes.