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Measurement of atmospheric constituents by selective ion mass spectrometry

This project is the continuation of contract EV5V-CT92-0062 (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). The final goal of both projects is to develop a method for stratospheric trace gas detection based on chemical ionization. A balloon borne instrument has been developed, consisting of a Mattauch Herzog mass spectrometer and a special ion source, allowing the derivation of stratospheric nitric acid profiles between altitudes of 20 and 30 km. This method is now being extended to measure other gases such as dinitrogen pentoxide (N(2)O(5)), chlorine nitrate (ClONO(2)) and hydrochloric acid (HCl) and to enlarge the altitude domain covered by the measurements (down to 15 km if possible). In parallel laboratory measurements of ion-molecule reaction rates, required for the analysis of the flight data, were performed. It is also the intention to investigate by laboratory testing, the future use of the instrument for ambient ion measurements, to provide additional information about stratospheric sulphuric acid (H(2)SO(4)).
At present a balloon flight has been conducted with the improved instrument, containing 4 different ion sources. Nitric acid profiles were derived from the chlorine discharge ion source, the CO(3)(-) photo-electric ion source and the new CF(3)O(-) ion source. Preliminary results obtained with the latter source show the possibility of deriving HCl and ClONO(2) profiles. Improvements of this source are required and are underway. The results obtained with the iodine discharge ion source, intended to infer N(2)O(5) data, are not clear yet and their analysis require further laboratory measurements. Laboratory studies of several important ion-molecule reactions involved in the HNO(3) ion chemistry have also been performed.

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Belgisch Instituut voor Ruimte-Aëronomie
Ringlaan 3
1180 Bruxelles
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