Abstract
(Englisch)
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The major objectives of this proposal is to further develop and refine a method for the simultaneous in-situ measurement of stratospheric HNO3, N2O5 and ClONO2. As such it is a continuation of the former projects SIDAMS and MACSIMS I in the previous and ongoing collaborations between the three research groups of the Belgian Institute for Space Aeronomy (BIRA), the 'Laboratoire de Physique et Chemie de l'Environment du CNRS' at the University of Orléans, and the Physikalisches Institut of the University of Bern. Within these projects a balloon borne instrument has been developed, which is based upon active chemical ionization, using specially designed ion sources (Cln- , In- , CO3- , and CF3O- ) and a new magnetic double focusing mass spectrometer with simultaneous ion detection.
Two successful balloon flights have been realized within the MACSIMS II project (Gap 1997 and Gap 1999). The data of these flights have been analyzed. Additionally the data of the balloon flight performed in León in 1995 (within the MACSIMS I project) were also further analyzed.
As a final conclusion, we can state that the CIMS (Chemical Ionization Mass Spectrometry) methods developed to measure nitric acid within the MACSIMS II project lead to good results, which are comparable with those obtained by other methods. Compared to the commonly used optical spectroscopy methods, this CIMS technique possesses the important advantage of performing local measurements, which is of prime interest for the monitoring of short lived species. Nighttime measurements are also easily performed with this technique and the data reduction is also relatively simple.
Although the derivation of other trace gases such as N2O5, ClONO2 and HCl is presently hampered by a complex ion chemistry, not yet fully understood, we believe that the use of CF3O- as a source ion for the measurement of stratospheric ClONO2 and HCl, deserves further investigation. Getting a better insight into the ion-molecule chemistry of these two trace gases through laboratory measurements seems a feasible objective, to which we will devote our efforts in the coming year. The laboratory apparatuses which were built within this project and which will be completed by a Selected Ion Flow Tube in the near future will be our main tools for this study.
The flight instrument and associated ground hard- and software as well as the technology developed within this project have been working satisfactory in all balloon flights and are worth further developing for future CIMS measurements.
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