SIDAMS (Simultaneous Ion Detection in Atmospheric Mass Spectrometry)

This flight was part of the development of a novel balloon-borne mass spectrometer in the context of the SIDAMS (Simultaneous Ion Detection in Atmospheric Mass Spectrometry) project. The experiment focused on detecting trace gases through passive and active ion mass spectrometry. It originated from a collaboration between the Belgian Institute for Space Aeronomy, the Physikalisches Institut of the University of Bern, and the Laboratoire de Chimie et Physique de l'Environnement of the CNRS. The aim was to probe trace gases such as nitric oxides, nitric acid, water vapor, and sulfuric acid, which are linked to Polar Stratospheric Cloud (PSC) formation and ozone depletion.

The passive chemical ionization technique allowed trace gas detection via the steady-state method and the thermodynamic equilibrium method. The steady-state method depended on the reactivity of atmospheric ions with trace gases, forming characteristic product ions. By analyzing the abundance ratios of primary and product ions, the concentration profiles of compounds like acetonitrile and sulfuric acid were derived for altitudes between 20 and 45 kilometers. Despite its sensitivity, this method was limited to gases reacting with ambient cluster ions and suffered from potential errors due to collision-induced dissociation (CID) during sampling. The thermodynamic equilibrium method relied on association reactions forming ion clusters, such as H3O+(H2O)n and NO3-(HNO3)n. From equilibrium constants and temperature, trace gas partial pressures were derived. However, this method was even more CID-sensitive, yielding reliable nitric acid mixing ratios only above 30 kilometers altitude.

The new mass spectrometer, designed to address these challenges, featured higher sensitivity, increased mass resolution, and reduced CID effects. Its principal components included a modified Mattauch-Herzog mass analyzer (mass range 12 to 500 amu), an ion detector for simultaneous measurement, a high-speed cryopumping system, and an RF octopole field combined with an electrostatic ion lens for ion focusing. Two instruments were to be built under the SIDAMS project, one for positive ions and one for negative ions. Balloon flights from Aire-sur-l'Adour, France, were planned to test these devices. Laboratory tests indicated an eightfold sensitivity increase and minimized CID effects with the positive ion spectrometer, enabling CH3CN and H2SO4 concentration profiling. The negative ion spectrometer was expected to profile H2SO4 and HNO3.

The active chemical ionization technique expanded the instrument's capabilities through an added ion source, producing ions like Cl- and I- to react with trace gases. The product ion ratios from these reactions allowed the determination of nitric acid and dinitrogen pentoxide concentrations, exploiting reaction rate constants established through laboratory studies.

Balloon launched on: 5/21/1991
Launch site: Centre de Lancement de Ballons CLBA, Aire Sur L'Adour, Landes, France  
Balloon launched by: Centre National d'Etudes Spatiales (CNES)
Balloon manufacturer/size/composition: Zero Pressure Balloon  
End of flight (L for landing time, W for last contact, otherwise termination time): 5/21/1991

• Simultaneous Ion Detection in Atmospheric Mass Spectrometry (SIDAMS). Trace Gas Detection Through Passive and Active Ion Mass Spectrometry Using a new Type of Balloon Borne Mass Spectrometer Status report of the project