References

ACPD

Atmospheric Chemistry and Physics Discussions

ACPD

1680-7375

Copernicus GmbH

Göttingen, Germany

10.5194/acpd-10-5999-2010

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

Assonov

S. S.

¹ ² ³ Brenninkmeijer

C. A. M.

² Schuck

T. J.

² Taylor

European Commission, Joint Research Centre, Institute for Reference Materials and Measurements, Geel, Belgium

Max Planck Institute for Chemistry, Atmospheric Chemistry Division, Mainz, Germany

presently at: Institute for Geology and Mineralogy, University of Köln, Germany

01 03 2010

10 3 5999 6057

This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

This article is available from http://www.atmos-chem-phys-discuss.net/10/5999/2010/acpd-10-5999-2010.html

The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/10/5999/2010/acpd-10-5999-2010.pdf

The project CARIBIC (<a href="http://caribic-atmospheric.com"target="_blank">http://caribic-atmospheric.com</a>) aims to study atmospheric chemistry and transport by regularly measuring many compounds 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 in detail together with supporting trace gas data. 509 CARIBIC-2 samples (highest precision and accuracy δ13C(CO2) and δ18O(CO2) data) from June 2007 until March 2009, together with CARIBIC-1 samples (flights between November 1999 and April 2002, 350 samples in total, 270 for NH, mostly δ13C(CO2) data) give a fairly extensive, unique data set for the NH free troposphere and the UT/LMS region. To compare data from different years a de-trending is applied. In the UT/LMS region δ13C(CO2), δ18O(CO2) and CO2 are found to correlate well with stratospheric tracers, in particular N2O. These correlations are in good agreement with current understanding of stratospheric circulation. δ18O(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. Correlations between δ13C(CO2) and CO2 are observed both within single flight(s) covering long distances and for certain seasons. The overall variability in de-trended δ13C(CO2) and CO2 for CARIBIC-1 and CARIBIC-2 are similar and basically agree with each other, which also underscores the high quality of measurement. Based on all correlations, we discuss that CO2 distribution in the NH FT and UT (at CARIBIC flight routes) is regulated by uplift and pole-wards transport of tropical air up to approximately 50° N. 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. A logical next step will be global scale modeling of δ13C and especially δ18O, which is linked to the hydrological cycle.

References 1

Allison, C. E., Francey, R. J., and Meijer, H. A. J.: Recommendation for the reporting of stable isotope measurements of carbon and oxygen in CO2 gas., IAEA-TECDOC-825, Vienna, IAEA-TECDOC-825, 155–162, 1995.

Andrews, A. E., Boering, K. A., Daube, B. C., Wofsy, S. C., Loewenstein, M., Jost, H., Podolske, J. R., Webster, C. R., Herman, R. L., Scott, D. C., Flesch, G. J., Moyer, E. J., Elkins, J. W., Dutton, G. S., Hurst, D. F., Moore, F. L., Ray, E. A., Romashkin, P. A., and Strahan, S. E.: Mean ages of stratospheric air derived from in situ observations of CO2, CH4, and N2O, J. Geophys. Res.-Atmos., 106, 32295–32314, 2001.

Assonov, S., Taylor, P., and Brenninkmeijer, C. A. M.: A system for high-quality CO2 isotope analyses of air samples collected by the CARIBIC Airbus A340-600, Rapid Commun. Mass Spectrom., 23, 1347–1363, 2009a.

Assonov, S. S. and Brenninkmeijer, C. A. M.: A re-determination of absolute values for $^17$R$_\rm VPDB-CO_2$ and $^17$R$_\rm VSMOW$, Rapid Commun. Mass Spectrom., 17, 1017–1029, 2003.

Assonov, S. S., Brenninkmeijer, C. A. M., Zahn, A., and Koeppel, C.: CO2 isotopic composition in the upper troposphere: the project CARIBIC, 14th WMO/IAEA Meeting of Experts on Carbon Dioxide Concentration and Related Tracers Measurement Techniques, Helsinki, Finnland, 9–22 September 2007, 2007.

Assonov, S. S., Brenninkmeijer, C. A. M., Koeppel, C., and Röckmann, T.: CO2 isotope analyses using large air samples collected on intercontinental flights by the CARIBIC Boeing 767, Rapid Commun. Mass Spectrom., 23, 822–830, 2009b.

Bender, M. L., Ho, D. T., Hendricks, M. B., Mika, R., Battle, M. O., Tans, P. P., Conway, T. J., Sturtevant, B., and Cassar, N.: Atmospheric O2/N2 changes, 1993-2002: Implications for the partitioning of fossil fuel CO2 sequestration, Global Biogeochem. Cy., 19, GB4017, doi:10.1029/2004gb002410, 2005.

Bischof, W. and Bolin, B.: Space and time variations of CO2 content of troposphere and lower stratosphere, Tellus, 18, 155–159, 1966.

Boenisch, H., Hoor, P., Gurk, C., Feng, W., Chipperfield, M., Engel, A., and Bregman, B.: Model evaluation of CO2 and SF$_6$ in the extratropical UT/LS region, J. Geophys. Res., 113, D06101, doi:10.1029/2007JD008829, 2008.

Boering, K. A., Jackson, T., Hoag, K. J., Cole, A. S., Perri, M. J., Thiemens, M., and Atlas, E.: Observations of the anomalous oxygen isotopic composition of carbon dioxide in the lower stratosphere and the flux of the anomaly to the troposphere, Geophys. Res. Lett., 31, L03109, doi:03110.01029/02003GL018451, 2004.

Bowen, G. J., West, J. B., Vaughn, B. H., Dawson, T. E., Ehleringer, J. R., Fogel, M. L., Hobson, K., Hoogewerff, J., Kendall, C., Lai, C.-T., Miller, C. C., Noone, D., Schwarcz, H., and Still, C. J.: Isoscapes to Address Large-Scale Earth Science Challenges, EOS, Transactions American Geophysical Union, 90(13), 109–110, doi:10.1029/2009EO130001, 2009.

Bowling, D. R., Pataki, D. E., and Randerson, J. T.: Carbon isotopes in terrestrial ecosystem pools and CO2 fluxes, New Phytol., 178, 24–40, 2008.

Brand, W. A., Assonov, S. S., and Coplen, T. B.: Correction for the $^17$O interference in $\delta^13$C measurements when analyzing CO2 with stable isotope mass spectrometry, Pure Anal. Chem., submitted, 2009.

Brenninkmeijer, C. A. M., Kraft, P., and Mook, W. G.: Oxygen Isotope Fractionation Between CO2 and H2O, Isotope Geoscience, 1, 181–190, 1983.

Brenninkmeijer, C. A. M., Crutzen, P. J., Fischer, H., Gusten, H., Hans, W., Heinrich, G., Heintzenberg, J., Hermann, M., Immelmann, T., Kersting, D., Maiss, M., Nolle, M., Pitscheider, A., Pohlkamp, H., Scharffe, D., Specht, K., and Wiedensohler, A.: CARIBIC - Civil aircraft for global measurement of trace gases and aerosols in the tropopause region, J. Atmos. Ocean. Technol., 16, 1373–1383, 1999.

Brenninkmeijer, C. A. M., Crutzen, P., Boumard, F., Dauer, T., Dix, B., Ebinghaus, R., Filippi, D., Fischer, H., Franke, H., Frieß, U., Heintzenberg, J., Helleis, F., Hermann, M., Kock, H. H., Koeppel, C., Lelieveld, J., Leuenberger, M., Martinsson, B. G., Miemczyk, S., Moret, H. P., Nguyen, H. N., Nyfeler, P., Oram, D., O'Sullivan, D., Penkett, S., Platt, U., Pupek, M., Ramonet, M., Randa, B., Reichelt, M., Rhee, T. S., Rohwer, J., Rosenfeld, K., Scharffe, D., Schlager, H., Schumann, U., Slemr, F., Sprung, D., Stock, P., Thaler, R., Valentino, F., Van Velthoven, P., Waibel, A., Wandel, A., Waschitschek, K., Wiedensohler, A., Xueref-Remy, I., Zahn, A., Zech, U., and Ziereis, H.: Civil Aircraft for the regular investigation of the atmosphere based on an instrumented container: The new CARIBIC system, Atmos. Chem. Phys., 7, 4953–4976, 2007.

Callendar, G. S.: The Artificial Production of Carbon Dioxide and Its Influence on Temperature, Q. J. Roy. Meteorol. Soc., 64, 223–240, 1938.

Ciais, P., Tans, P. P., White, J. W. C., Trolier, M., Francey, R. J., Berry, J. A., Randall, D. R., Sellers, P. J., Collatz, J. G., and Schimel, D. S.: Partitioning of Ocean and Land Uptake of CO2 as Inferred by Delta-C-13 Measurements from the NOAA Climate Monitoring and Diagnostics Laboratory Global Air Sampling Network, J. Geophys. Res.-Atmos., 100, 5051–5070, 1995.

Ciais, P., Denning, A. S., Tans, P. P., Berry, J. A., Randall, D. A., Collatz, G. J., Sellers, P. J., White, J. W. C., Trolier, M., Meijer, H. A. J., Francey, R. J., Monfray, P., and Heimann, M.: A three-dimensional synthesis study of $\delta^18$O in atmospheric CO2. 1. Surface fluxes, J. Geophys. Res.-Atmos., 102, 5857–5872, 1997.

Ciais, P., Cuntz, M., Scholze, M., Mouillot, F., Peylin, P., and Gitz, V.: Remarks on the use of 13C and 18O isotopes in Atmospheric CO2 to Quantify biospheric carbon fluxes, in: Stable Isotopes and Biosphere Atmosphere Interactions, Academic Press, San Diego, CA, USA, 235–267, 2005.

CONTRAIL 2009: CO2 flask event Comprehensive Observation Network for TRace gases by AIrLiner (CONTRAIL), Period 1993-04-23 to 2007-12-20, Version 2008-08-05, available online at: http://gaw.kishou.go.jp/, 2009.

Dlugokencky, E. J., Steele, L. P., Lang, P. M., and Masarie, K. A.: The growth rate and distribution of atmospheric methane, J. Geophys. Res., 99, 17021–17043, 1994.

Engel, A., Mobius, T., Bonisch, H., Schmidt, U., Heinz, R., Levin, I., Atlas, E., Aoki, S., Nakazawa, T., Sugawara, S., Moore, F., Hurst, D., Elkins, J., Schauffler, S., Andrews, A., and Boering, K.: Age of stratospheric air unchanged within uncertainties over the past 30 years, Nature Geosci, 2, 28–31, 2009.

Francey, R. J., Allison, C. E., Etheridge, D. M., Trudinger, C. M., Enting, I. G., Leuenberger, M., Langenfelds, R. L., Michel, E., and Steele, L. P.: A 1000-year high precision record of $\delta^13$C in atmospheric CO2, Tellus, 51B, 170–193, 1999.

GLOBALVIEW-CO2: Cooperative Atmospheric Data Integration Project – Carbon Dioxide. CD-ROM, NOAA ESRL, Boulder, Colorado, online available via anonymous ftp to ftp.cmdl.noaa.gov, path: ccg/co2/GLOBALVIEW, 2009.

GLOBALVIEW-CO2C13: Cooperative Atmospheric Data Integration Project – $d^13$C of Carbon Dioxide. CD-ROM, NOAA ESRL, Boulder, Colorado, online available via anonymous ftp to ftp.cmdl.noaa.gov, path: ccg/co2c13/GLOBALVIEW, 2009.

Hall, T. M., Waugh, D. W., Boering, K. A., and Plumb, R. A.: Evaluation of transport in stratospheric models, J. Geophys. Res.-Atmos., 104, 18815–18839, 1999.

Hegglin, M. I. and Shepherd, T. G.: O3-N2O correlations from the Atmospheric Chemistry Experiment: Revisiting a diagnostic of transport and chemistry in the stratosphere, J. Geophys. Res., 112, D19301, doi:10.1029/2006jd008281, 2007.

Hoor, P., Gurk, C., Brunner, D., Hegglin, M. I., Wernli, H., and Fischer, H.: Seasonality and extent of extratropical TST derived from in-situ CO measurements during SPURT, Atmos. Chem. Phys., 4, 1427–1442, 2004.

Hoor, P., Fischer, H., and Lelieveld, J.: Tropical and extratropical tropospheric air in the lowermost stratosphere over Europe: A CO-based budget, Geophys. Res. Lett., 32, L07802, doi:07810.01029/02004GL022018, 2005.

Jiang, X., Ku, W. L., Shia, R.-L., Li, Q., Elkins, J. W., Prinn, R. G., and Yung, Y. L.: Seasonal cycle of N2O: Analysis of data, Global Biogeochem. Cy., 21, GB1006, doi:10.1029/2006gb002691, 2007.

Keeling, C. D.: The concentration and isotopic abundances of carbon dioxide in rural and marine air, Geochim. Cosmochim. Acta, 24, 277–298, 1961.

Köppe, M., Hermann, M., Brenninkmeijer, C. A. M., Heintzenberg, J., Schlager, H., Schuck, T., Slemr, F., Sprung, D., van Velthoven, P. F. J., Wiedensohler, A., Zahn, A., and Ziereis, H.: Origin of aerosol particles in the mid latitude and subtropical upper troposphere and lowermost stratosphere from cluster analysis of CARIBIC data, Atmos. Chem. Phys., 9, 8413–8430, 2009.

Lai, S. C., Baker, A. K., Schuck, T. J., van Velthoven, P., Oram, D. E., Zahn, A., Hermann, M., Weigelt, A., Slemr, F., Brenninkmeijer, C. A. M., and Ziereis, H.: Pollution events observed during CARIBIC flights in the upper troposphere between South China and the Philippines, Atmos. Chem. Phys., 10, 1649–1660, 2010.

Lämmerzahl, P., Röckmann, T., Brenninkmeijer, C. A. M., Krankowsky, D., and Mauersberger, K.: Oxygen isotope composition of stratospheric carbon dioxide, Geophys. Res. Lett., 29, 1582, doi:1510.1029/2001GL014343, 2002.

Levin, I., Allison, C., Brand, W., Conway, Delmotte, M., Facklam, C., Francey, R., Hammer, S., Huang, L., Jordan, A., Langenfelds, R., Machida, T., Meijer, H., Mukai, H., Neubert, R., Sabasch, M., Schmidt, M., Steele, P., Steinberg, B., Ramonet, M., Rothe, M., Vaughn, B., and Worthy, D.: Five Years of International Flask Intercomparison (Sausage Flask ICP) 2002-2007, 14th WMO/IAEA Meeting of Experts on Carbon Dioxide Concentration and Related Tracers Measurement Techniques, Helsinki, Finland, 10–13 September 2007, 2007.

Levin, I. and Karstens, U.: Inferring high-resolution fossil fuel CO2 records at continental sites from combined $^14$CO2 and CO observations, Tellus B – Chem. Phys. Meteorol., 59, 245–250, 2007.

Levin, I., Hammer, S., Kromer, B., and Meinhardt, F.: Radiocarbon observations in atmospheric CO2: Determining fossil fuel CO2 over Europe using Jungfraujoch observations as background, Sci. Total Environ., 391, 211–216, 10.1016/j.scitotenv.2007.10.019, 2008.

Lintner, B. R., Buermann, W., Koven, C. D., and Fung, I. Y.: Seasonal circulation and Mauna Loa CO2 variability, J. Geophys. Res., 111, D13104, doi:10.1029/2005JD006535, 2006.

Masarie, K. A. and Tans, P. P.: Extension and integration of atmospheric carbon dioxide data into a globally consistent measurement record, J. Geophys. Res., 100, 11593–11610, 1995.

Matsueda, H., Machida, T., Sawa, Y., Nakagawa, Y., Hirotani, K., Ikeda, H., Kondo, N., and Goto, K.: Evaluation of atmospheric CO2 measurements from new flask air sampling of JAL airliner observations, Meteorol. Geophys., 59, 1–17, doi:10.2467/mripapers.2459.2461, 2008.

Matsueda, H. H., Inoue, Y., and Ishii, M.: Aircraft observation of carbon dioxide at 8–13 km altitude over the western Pacific from 1993 to 1999, Tellus, 1–21, 2002.

Miller, J. B., Tans, P. P., White, J. W. C., Conway, T. J., and Vaughn, B. W.: The atmospheric signal of terrestrial carbon isotopic discrimination and its implication for partitioning carbon fluxes, Tellus B, 55, 197–206, 2003.

Miyazaki, K., Patra, P. K., Takigawa, M., Iwasaki, T., and Nakazawa, T.: Global-scale transport of carbon dioxide in the troposphere, J. Geophys. Res., 113, D15301, doi:10.1029/2007JD009557, 2008.

Miyazaki, K., Machida, T., Patra, P. K., Iwasaki, T., Sawa, Y., Matsueda, H., and Nakazawa, T.: Formation mechanisms of latitudinal CO2 gradients in the upper troposphere over the subtropics and tropics, J. Geophys. Res., 114, D03306, doi:10.1029/2008JD010545, 2009.

Nevison, C. D., Kinnison, D. E., and Weiss, R. F.: Stratospheric influences on the tropospheric seasonal cycles of nitrous oxide and chlorofluorocarbons, Geophys. Res. Lett., 31, L20103, doi:10.1029/2004GL020398, 2004.

Nevison, C. D., Mahowald, N. M., Weiss, R. F., and Prinn, R. G.: Interannual and seasonal variability in atmospheric N2O, Global Biogeochem. Cy., 21, GB3017, doi:10.1029/2006GB002755, 2007.

Pan, L. L., Hintsa, E. J., Stone, E. M., Weinstock, E. M., and Randel, W. J.: The seasonal cycle of water vapor and saturation vapor mixing ratio in the extratropical lowermost stratosphere, Journal of Geophysical Research, 105, 26519–26530, 2000.

Pan, L. L., Randel, W. J., Gary, B. L., Mahoney, M. J., and Hintsa, E. J.: Definitions and sharpness of the extratropical tropopause: A trace gas perspective, J. Geophys. Res.-Atmos., 109, D23103, doi:10.1029/2004JD004982, 2004.

Pan, L. L., Bowman, K. P., Shapiro, M., Randel, W. J., Gao, R. S., Campos, T., Davis, C., Schauffler, S., Ridley, B. A., Wei, J. C., and Barnet, C.: Chemical behavior of the tropopause observed during the Stratosphere-Troposphere Analyses of Regional Transport experiment, J. Geophys. Res., 112, D18110,, doi:10.1029/2007jd008645, 2007.

Pan, L. L., Randel, W. J., Gille, J. C., Hall, W. D., Nardi, B., Massie, S., Yudin, V., Khosravi, R., Konopka, P., and Tarasick, D.: Tropospheric intrusions associated with the secondary tropopause, J. Geophys. Res., 114, D10302, doi:10.1029/2008jd011374, 2009.

Pataki, D. E., Ehleringer, J. R., Flanagan, L. B., Yakir, D., Bowling, D. R., Stil, C. J., Buchmann, N., Kaplan, J. O., and Berry, J. A.: The application and interpretation of Keeling plots in terrestrial carbon cycle research, Global Biogeochem. Cy., 17, 1022, doi:1010.1029/2001GB001850, 2003.

Patra, P. K., and Maksyutov, S.: Incremental approach to the optimal network design for CO2 surface source inversion, Geophys. Res. Lett., 29(10), 1459, doi:10.1029/2001GL013943, 2002.

Patra, P. K., Maksyutov, S., and Group Authors: Transcom 3 Modelers: Sensitivity of Optimal Extension of CO2 Observation Networks to Model Transport, Tellus, 55B, 498–511, 2003.

Quay, P., Sonnerup, R., Westby, T., Stutsman, J., and McNichol, A.: Changes in the 13C/12C of dissolved inorganic carbon in the ocean as a tracer of anthropogenic CO2 uptake, Global Biogeochem. Cy., 17(1), 1004 doi:10.1029/2001GB001817, 2003.

Rayner, P. J., Law, R. M., Allison, C. E., Francey, R. J., Trudinger, C. M., and Pickett-Heaps, C.: Interannual variability of the global carbon cycle (1992-2005) inferred by inversion of atmospheric CO2 and $^13$CO2 measurements, Global Biogeochem. Cy., 22, GB3008, doi:10.1029/2007gb003068, 2008.

Rhee, T. S., Brenninkmeijer, C. A. M., Mühle, J., van Velthoven, P. F. J., Hermann, M., Zahn, A., Oram, D. E., Scharffe, D. H., Koeppel, C., Fischer, H., and Lelieveld, J.: A case study of rapid mixing across the extratropical tropopause based on Civil Aircraft for the Regular Investigation of the Atmosphere Based on an Instrumented Container (CARIBIC) observations, J. Geophys. Res. - Atmos., 110, D22301, doi:22310.21029/22005JD005890, 2005.

Schuck, T. J., Brenninkmeijer, C. A. M., Slemr, F., Xueref-Remy, I., and Zahn, A.: Greenhouse gas analysis of air samples collected onboard the CARIBIC passenger aircraft, Atmos. Meas. Tech., 2, 449–464, 2009.

Schuck, T. J., Brenninkmeijer, C. A. M., Baker, A. K., Slemr, F., Velthoven, P. F. J. v., and Zahn, A.: Greenhouse Gas Relationships in the Indian Summer Monsoon Plume Measured by the CARIBIC 2 Passenger Aircraft, to be submitted, Atmos. Chem. Phys. Discuss., 10, 2031–2087, 2010.

Shia, R.-L., Liang, M.-C., Miller, C. E., and Yung, Y. L.: CO2 in the upper troposphere: Influence of stratosphere-troposphere exchange, Geophys. Res. Lett., 33, L14814, doi:10.1029/2006gl026141, 2006.

Still, C. J., Riley, W. J., Biraud, S. C., Noone, D. C., Buenning, N. H., Randerson, J. T., Torn, M. S., Welker, J., White, J. W. C., Vachon, R., Farquhar, G. D., and Berry, J. A.: Influence of clouds and diffuse radiation on ecosystem-atmosphere CO2 and CO$^18$O exchanges, J. Geophys. Res., 114, G01018, doi:10.1029/2007JG000675, 2009.

Stohl, A., Bonasoni, P., Cristofanelli, P., Collins, W., Feichter, J., Frank, A., Forster, C., Gerasopoulos, E., Gaggeler, H., James, P., Kentarchos, T., Kromp-Kolb, H., Kruger, B., Land, C., Meloen, J., Papayannis, A., Priller, A., Seibert, P., Sprenger, M., Roelofs, G. J., Scheel, H. E., Schnabel, C., Siegmund, P., Tobler, L., Trickl, T., Wernli, H., Wirth, V., Zanis, P., and Zerefos, C.: Stratosphere-troposphere exchange: A review, and what we have learned from STACCATO, J. Geophys. Res., 108D12, 8516, doi:10.1029/2002jd002490, 2003.

Strahan, S. E., Douglass, A. R., Nielsen, J. E., and Boering, K. A.: The CO2 seasonal cycle as a tracer of transport, J. Geophys. Res.-Atmos., 103, 13729–13741, 1998.

Turnbull, J. C., Miller, J. B., Lehman, S. J., Tans, P. P., Sparks, R. J., and Southon, J.: Comparison of 14CO2, CO, and SF6 as tracers for recently added fossil fuel CO2 in the atmosphere and implications for biological CO2 exchange, Geophys. Res. Lett., 33, L01817, doi:10.1029/2005gl024213, 2006. %

%White, J. W. C. and Vaughn, B. W.: University of Colorado, Institute of %Arctic and Alpine Research (INSTAAR), Stable Isotopic Composition of %Atmospheric Carbon Dioxide ($^13$C and $^18$O) from the NOAA ESRL Carbon %Cycle Cooperative Global Air Sampling Network, 1990–2007, Version: %2009-06-01, ftp://ftp.cmdl.noaa.gov/ccg/co2c13/flask/event/. 2009.

13th_WMO/IAEA_Meeting: 13th WMO/IAEA Meeting of Experts on Carbone Dioxide Concentration and Related Tracers Measurement Techniques, Boulder, Colorado, USA, (WMO TD No. 1359), WMO/GAW report No. 161, http://www.wmo.ch/web/arep/gaw/gawreports.html, Expert Group Recommendations, 19–22 September 2005.

Zahn, A., Brenninkmeijer, C. A. M., Asman, W. A. H., Crutzen, P. J., Heinrich, G., Fischer, H., Cuijpers, J. W. M., and van Velthoven, P. F. J.: Budgets of O3 and CO in the upper troposphere: CARIBIC passenger aircraft results 1997–2001, J. Geophys. Res.-Atmos., 107(D17), 4337, doi:10.1029/2001jd001529, 2002.

Zahn, A., Brenninkmeijer, C. A. M., and van Velthoven, P. F. J.: Passenger aircraft project CARIBIC 1997–2002, Part II: the ventilation of the lowermost stratosphere, Atmos. Chem. Phys. Discuss., 4, 1119–1150, 2004a.

Zahn, A., Brenninkmeijer, C. A. M., and van Velthoven, P. F. J.: Passenger aircraft project CARIBIC 1997–2002, Part I: the extratropical chemical tropopause, Atmos. Chem. Phys. Discuss., 4, 1091–1117, 2004b.