Abstract
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.
Highlights
CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrumented Container, www.caribic-atmospheric.com) is one of three current at-mospheric chemistry and composition programs based on commercial passenger aircraft (Brenninkmeijer et al, 2005; IGAC, 2007)
Schuck mospheric chemistry and composition programs based on commercial passenger aircraft (Brenninkmeijer et al, 2005; IGAC, 2007). Such programs provide the possibility of regularly monitoring atmospheric trace constituents on a longterm basis, i.e. over several years. These aircraft projects are unique in that large sections of the globe are covered, that background tropospheric air is probed, and that, depending on the flight routes, a large fraction of the flight time is spent in the tropopause region and the lowermost stratosphere
The working standard that is used as the running standard for the analysis of the CARIBIC whole air samples is calibrated against the NOAA standards monthly the day before the analysis of samples
Summary
CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrumented Container, www.caribic-atmospheric.com) is one of three current at-. The total sampling time is the sum of the time interval between the switching points of the outlet and the inlet valve and the time needed to replace the air volume inside the canister during the flushing period at the respective ambient pressure. As the pressure measured in-flight is the sum of ambient pressure and ram pressure and depends on the container temperature, the actual pressure in the laboratory at the time of analysis varies and is lower than 4.5 bar It ranges from 3.5 to 4.2 bar corresponding to a sample volume of about 9 to 11 l (STP). 1.5 min after the start of a cycle valve 1 is switched and the respective carrier gas starts flowing through each sample loop. If they agree within their errors, the mixing ratio of a sample is taken to be the average of both numbers
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