Atmospheric Measurement Techniques Discussions www.atmos-meas-tech-discuss.net 1867-8610 2 6 2009 10.5194/amtd-2-3127-2009 http://www.atmos-meas-tech-discuss.net/2/3127/2009/ http://www.atmos-meas-tech-discuss.net/2/3127/2009/amtd-2-3127-2009.html http://www.atmos-meas-tech-discuss.net/2/3127/2009/amtd-2-3127-2009.pdf 3127 3152 2009-12-04 High-accuracy continuous airborne measurements of greenhouse gases (CO₂ and CH₄) during BARCA H. Chen hchen@bgc-jena.mpg.de J. Winderlich C. Gerbig A. Hoefer C. W. Rella E. R. Crosson A. D. Van Pelt J. Steinbach O. Kolle V. Beck B. C. Daube E. W. Gottlieb V. Y. Chow G. W. Santoni S. C. Wofsy Max Planck Institute for Biogeochemistry, 07745 Jena, Germany Picarro, Inc., Sunnyvale, CA 94085, USA Department of Earth and Planetary Sciences and the Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA High-accuracy continuous measurements of greenhouse gases (CO₂ and CH₄) during the BARCA (Balanço Atmosférico Regional de Carbono na Amazônia) phase B campaign in Brazil in May 2009 were accomplished using a newly available analyzer based on the cavity ring-down spectroscopy (CRDS) technique. This analyzer was flown without a drying system or any in-flight calibration gases. Water vapor corrections associated with dilution and pressure-broadening effects for CO₂ and CH₄ were derived from laboratory experiments employing measurements of water vapor by the CRDS analyzer. Before the campaign, the stability of the analyzer was assessed by laboratory tests under simulated flight conditions. During the campaign, a comparison of CO₂ measurements between the CRDS analyzer and a nondispersive infrared (NDIR) analyzer on board the same aircraft showed a mean difference of 0.22±0.09 ppm for all flights over the Amazon rain forest. At the end of the campaign, CO₂ concentrations of the synthetic calibration gases used by the NDIR analyzer were determined by the CRDS analyzer. After correcting for the isotope and the pressure-broadening effects that resulted from changes of the composition of synthetic vs. ambient air, and applying those concentrations as calibrated values of the calibration gases to reprocess the CO₂ measurements made by the NDIR, the mean difference between the CRDS and the NDIR during BARCA was reduced to 0.05±0.09 ppm, with the mean standard deviation of 0.23±0.05 ppm. 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