Abstract
Balloon-borne composition measurements of stratospheric negative ions were carried out at altitudes between about 30 and 40 km using two improved mass spectrometer probes with high sensitivity and mass resolution mounted on a gondola carried by a 350,000 m 3 balloon. In order to minimize the risk of contamination, data were taken only at float altitude and during balloon descent. Besides the major ion species, HSO 4 - (H 2SO 4) l(HNO 3) m and NO 3 - (HNO 3) n, various minor ion species were detected including also mixed clusters with H 2O, SO 3 and possibly HOCl ligands. It appears that the SO 3 ligands were formed by electric field-induced collisional cluster ion fragmentation during sampling of the ions into the mass spectrometer. Sulfuric acid vapor abundances inferred from the present negative ion composition data reveal the presence of a sulfuric acid vapor layer with a pronounced maximum around 37 km with a H 2SO 4 vapor concentration of about 3 × 10 6 cm −3, which is in accord with a previous measurement by our group. The occurrence of a maximum suggests that sulfuric acid vapor is efficiently removed at heights above about 37 km. Potential removal processes include photolysis, OH-attack and eventually also reactions with meteor smoke particles.
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