Upper stratosphere negative ion composition measurements and inferred trace gas abundances

Abstract

In situ composition measurements of atmospheric negative ions were made at 40.8 km altitude using a balloon-borne mass spectrometer with large mass range and improved mass resolution. The data obtained show marked differences compared to previous data obtained mostly around or below 33 km. It appears that these differences are mostly due to a higher atmospheric temperature, a lower nitric acid vapour abundance and a larger HSO 3-vapour abundance prevailing at the higher altitude. A particularly striking feature is the relatively large fractional abundance of HSO 3-containing cluster ions. Another interesting result is that nitric acid vapour abundances can be inferred from the negative ion composition data with better accuracy than is possible for lower altitudes. The reason being that collisional ion dissociation occurring during ion sampling is less disturbing. The inferred nitric acid vapour abundance for 40.8 km altitude is consistent with current 2-dimensional model calculations.