Strong evidence for the presence of aerosols well above the stratospheric H2SO4/H2O-aerosol layer was obtained by balloon-borne mass spectrometer measurements of ambient ions. The instrument was improved with respect to the detection of gaseous sodium compounds. From our measurements very low upper limits of gas phase sodium compounds (2¿103 cm-3 around 40 km) could relieably be inferred. This supports the hypothesis that all gas phase metal compounds from meteor ablation are efficiently removed by heterogeneous nucleation involving preexistent aerosols which may be identified as meteoritic or spaceflight debris. ¿ American Geophysical Union 1992