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Development and testing of a new balloon borne ion mass spectrometer and associated ion source for the measurement of stratospheric trace gases by active chemical ionization

Within this project a balloon borne instrument was developed for the measurement of stratospheric trace gases by chemical ionization mass spectrometry (CIMS). The instrument consisted of a flow tube and a special ion source coupled to a Mattauch Herzog mass spectrometer with simultaneous ion detection, which was developed within the SIDAMS project. The instrument was launched with 2 simple ion sources (a chlorine discharge and a photo-electric carbonate ion source) in May 1994 from the CNES balloon launching base in Aire sur l'Adour (France). From the ion spectra a nitric acid profile between 20 and 30 km altitude could be derived. For the data analysis, the results of measurements of ion-molecule reactions concerning polyhalide ions with nitric acid obtained in parallel in the laboratory, were used.

A switching ion source was developed, which allowed the alternating production of chloride and iodide ions with the aim of measuring simultaneously nitric acid and dinitrogen pentoxide. The instrument equiped with this new source was flown in November 1994 from the INTA base in Leon (Spain). Due to a problem with a high voltage power supply, the instrument could not work in the CIMS mode, but a large number of the major natural negative ions was obtained. A new flight was performed in November 1995 (also from Leon) with a newly designed high voltage power supply and with the switching discharge ion source and the photo-electric carbonate source. A detailed nitric acid profile could again be obtained from the chloride and carbonate spectra. The data obtained however with the discharge source in iodide mode, revealed that the ion chemistry was more complicated than expected and that a derivation of dinitrogen pentoxide mixing ratios was not straightforward and requires more laboratory studies.

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Belgisch Instituut voor Ruimte-Aëronomie
Ringlaan 3
1180 Bruxelles
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