Greenhouse gas analysis of air samples collected onboard the CARIBIC passenger aircraft

Abstract. CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container) is a long-term atmospheric measurement program based on the use of a comprehensive scientific instrument package aboard a commercial passenger aircraft. In addition to real-time measurements, whole air sampling is performed regularly at cruising altitudes in the tropical middle troposphere and the extra-tropical UT/LS region. Air samples are analyzed for greenhouse gases, NMHCs, halocarbons, and trace gas isotopic composition. The routinely performed greenhouse gas analysis comprises gas chromatography measurements of CO₂, CH₄, N₂O and SF₆.

The air sampling procedure, the GC system and its performance are described. Comparisons with similar systems employed in other laboratories and a comparison with results from a CO₂ in-situ analyzer that is also part of the CARIBIC instrumentation are shown. In addition, the time series of CO₂, obtained from the collection of 684 samples at latitudes between 30° N and 56° N on 21 round trips out of Germany to different destinations in Asia between November 2005 and October 2008, is presented. A time shift in the seasonal cycle of about one month was observed between the upper troposphere and the tropopause region. For two sets of return flights from Germany to the Philippines the relationship between the four greenhouse gases is briefly discussed.