First composition measurements of positive ions in the upper troposphere

Abstract First mass-spectrometric composition measurements of atmospheric ions between 3250 and 11700 m altitude are reported. They reveal the presence of very massive cluster ions, the majority of which cannot be attributed to a single hydrated ion family like, for example H + (H 2 O) n . The observed fraction of very massive ions increases with decreasing altitude. Masses as large as about 540 amu were observed at 8200 m altitude. Implications of the observations for ion and nucleation processes are discussed.