Title: Analysis of Accurate 13C and 18O Isotope Measurements of CO2 in CARIBIC Aircraft Air Samples from the Tropical Troposphere, and the Upper Troposphere/Lowermost Stratosphere
Citation: ATMOSPHERIC CHEMISTRY AND PHYSICS vol. 10 no. 3 p. 8575–8599
Publication Year: 2010
JRC N°: JRC54644
ISSN: 1680-7316
URI: www.atmos-chem-phys.net/10/8575/2010/
DOI: 10.5194/acp-10-8575-2010
Type: Articles in periodicals and books
Abstract: The project CARIBIC (http://caribic-atmospheric.com) aims to study atmospheric chemistry and composition by regularly measuring many compounds and species in the free troposphere (FT) and the upper troposphere-lowermost stratosphere (UT/LMS) by using passenger aircraft. Here CO2 concentrations and highly accurate isotope results are presented together with supporting trace gas data. About 500 samples (CARIBIC-2, highest precision and accuracy delta13C(CO2) and delta18O(CO2) data) from June 2007 until March 2009, together with about 350 CARIBIC-1 samples (mostly delta13C(CO2) from flights between November 1999 and April 2002) give a fairly extensive, unique data set for the free troposphere and the UT/LMS region in the NH. To compare data from different years a de-trending is applied. In the UT/LMS region delta13C(CO2), delta18O(CO2) and CO2 are found to correlate well with stratospheric tracers; particularly N2O. These correlations are in good agreement with current understanding of the stratospheric circulation. Delta18O(CO2) appears to be a useful, hitherto unused, tracer of atmospheric transport in the UT/LMS region. By filtering out the LMS data (based on N2O distribution), the isotope variations for the free and upper troposphere are obtained. These show however little latitudinal gradient, if any, and are in good agreement with the data of selected NOAA stations in NH tropics. For many flights delta13C(CO2) correlates well with CO2 within a single flight covering long distances. Correlations for certain seasons are also good, demonstrating a large scale seasonal source/sink balance. The overall variability in detrended delta13C(CO2) and CO2 for CARIBIC-1 and CARIBIC-2 are similar. Furthermore, all trends for CARIBIC-1 and CARIBIC-2 basically agree with each other, which independently underscores our understanding of involved processes as well as the high quality of the measurement. Based on all correlations, we discuss that CO2 distribution in FT and UT region in the NH is mostly regulated by uplift and pole-wards transport of tropical air. The main reasons for variability of signals in FT and UT (which is larger for the high spatial resolution sampling during CARIBIC-2) is mixing of different tropospheric air masses affected by CO2 sources and sinks. The effect of stratospheric flux appears to be limited. All in all it is demonstrated that CARIBIC produced new important and reliable data sets for little explored regions of the atmosphere. The paper carefully documents these data, of which we hope that they will assist global scale modeling of 13C and especially 18O, which is linked to the hydrological cycle.
JRC Directorate:Health, Consumers and Reference Materials

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