Unambiguous mass determination of major stratospheric positive ions

Abstract

There has been recent considerable interest in the stratospheric ion composition and ion chemistry, especially in view of its possible impact on aerosol formation^1,2 and the possibility of detection of minor constituents with very low concentrations^3,4. The first composition measurements of positive ions in the stratosphere conducted by a rocket-borne instrument⁵, revealed the existence of the theoretically predicted proton hydrates (PH)⁶ and also of some unexpected non-proton hydrates (NPH). (Proton hydrates are primarily ions of the form H⁺(H₂O)_n.) Because low altitude rocket data may be biased by shock wave effects, such as ion fragmentation, the need for balloon flights was strongly felt. In 1978, data obtained with balloon-borne instruments^7–9 partly confirmed and extended the rocket data. There have been several explanations^1,5,7,8,10 of the presence of the observed NPH, but the lack of resolution of the data means an ambiguity still exists about the exact masses of these ions. We report here the first high resolution mass spectra of positive ions in the stratosphere, at 34-km altitude, where the major mass peaks can be identified unambiguously.