Balloon‐borne mass spectrometer measurements of HNO 3 and HCN in the winter Arctic stratosphere — Evidence for HNO 3 ‐processing by aerosols

Altitude profiles of the stratospheric trace gases HNO 3 and HCN were simultaneously measured by a balloon‐borne mass spectrometer, which was launched on 13 February, 1992 at Kiruna (68°N, 20°E, Northern Sweden). The HCN‐profile is nearly constant, around 0.18 ppbv, which is similar to previously measured midlatitude data. The HNO 3 ‐profile measured below 24 km on the descent part of the balloon flight is similar to NO y (≲20ppbv), and becomes smaller than NO y above 24 km. Probably, the large HNO 3 , below 24 km, reflect heterogenous HNO 3 ‐formation by H 2 SO 4 ‐H 2 O aerosols from volcano Pinatubo. On ascent HNO 3 was substantially decreased around 18 to 24 km, which was possibly due to HNO 3 ‐dissolution in H 2 SO 4 ‐H 2 O aerosols.