A comparison of in-situ aircraft measurements of carbon dioxide

This discussion paper is/has been under review for the journal Atmospheric Measurement Techniques (AMT). Please refer to the corresponding final paper in AMT if available. Abstract In this paper we report vertical profiles of CO 2 measured with a cavity ring-down spectrometer (CRDS, Picarro, Inc., 2301-m) on a research aircraft from near ground level to 8 km above mean sea level (a.m.s.l.). The airborne platform employed in this study is an Alpha Jet aircraft operated from NASA Ames Research Center. Flights were un-5 dertaken to Railroad Valley, Nevada, USA, to coincide with overpasses of the Greenhouse Gases Observing Satellite (GOSAT). Ground based CO 2 was simultaneously measured using CRDS, also at the time and location of the airborne and satellite measurements. Results of three GOSAT coordinated aircraft profiles and ground based measurements in June 2011 are presented and discussed in this paper. The accuracy 10 of the CO 2 measurements has been determined based upon laboratory calibrations (WMO traceable standard) and pressure/temperature flight simulations in a test chamber. The 2-σ error bars for the CO 2 data presented here are ± 0.4 ppm. Our column CO 2 measurements, which include about 85 % of the tropospheric mass, are extrapolated , using two different techniques, to include the remainder of the tropospheric and 15 stratospheric CO 2. The data are then analyzed using the ACOS (Atmospheric CO 2 observations from space; JPL algorithm used to analyze XCO 2 from GOSAT data) averaging kernels. ACOS version 2.9 is used to interpret the GOSAT data in a collaborative effort between JPL and the GOSAT team. Column averaged CO 2 , XCO 2 , measured by GOSAT and analyzed from our data ranged from 388.1 to 390.5 ppm. Values of XCO 2 20 determined from our Alpha Jet measurements and from the GOSAT on three overflight days agree within 1 ppm or better (< 0.3 %).