BALLOON-BORNE MASS-SPECTROMETER MEASUREMENTS OF HNO3 AND HCN IN THE WINTER ARCTIC STRATOSPHERE - EVIDENCE FOR HNO3-PROCESSING BY AEROSOLS

Altitude profiles of the stratospheric trace gases HNO3 and HCN were s imultaneously measured by a balloon-borne mass spectrometer, which was launched on 13 February, 1992 at Kiruna (68-degrees-N, 20-degrees-E, Northern Sweden). The HCN-profile is nearly constant, around 0.18 ppbv , which is similar to previously measured midlatitude data. The HNO3-p rofile measured below 24 km on the descent part of the balloon flight is similar to NO(y) (less than or similar to 20ppbv), and becomes smal ler than NO(y) above 24 km. Probably, the large HNO3, below 24 km, ref lect heterogenous HNO3-formation by H2SO4-H2O aerosols from volcano Pi natubo. On ascent HNO3 was substantially decreased around 18 to 24 km, which was possibly due to HNO3-dissolution in H2SO4-H2O aerosols.