• 1. Determining the compositions of the particle cores (non-volatile and volatile components) is conducted mainly in the low stratosphere and down to the tropopause (above 30 km). In the higher part of the descent (above 80 km), it is expected that aerosols will be obtained by direct impaction on the filter. Below 80 km, where the pump becomes effective, the samples are obtained by filtration.
• 2. The second sample must be collected within the troposphere above the deep methane clouds (20 km).
• 3. Owing to mass constraints, the instrument is equipped with a single collector that must be used again after cleaning the oven, filter and product transfer lines.
• 4. The samples are analysed by using GCMS for a fixed portion of its life (approximately 20 min), knowing that this instrument must make at least one direct chromatographic analysis of the atmosphere's composition before surface impact.

In addition, because of the very short descent profile (120 min minimum), it was decided to make three transfers for each sample, each transfer using the direct MS mode. These will use, in turn, the oven at ambient temperature, 250°C and 600°C. A complete GCMS analysis, requiring about 10 min, is provided only for the first sample's pyrolysis sequence (transfer after 600°C heating). These pyrolysis products have to wait until GCMS has analysed the contents of the two gas enrichment cells that were sampled in the upper atmosphere. This implies that the use of the three gas chromatograph columns for analysing ACP aerosol pyrolysis products obtained at 600°C occurs at To+73 min (nominal altitude 25 km).

Operation Sequences during Descent

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