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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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Atmos. Meas. Tech., 10, 2163-2181, 2017
https://doi.org/10.5194/amt-10-2163-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
12 Jun 2017
AirCore-HR: a high-resolution column sampling to enhance the vertical description of CH4 and CO2
Olivier Membrive1,2, Cyril Crevoisier1, Colm Sweeney3,4, François Danis1, Albert Hertzog1, Andreas Engel5, Harald Bönisch5, and Laurence Picon2 1Laboratoire de Météorologie Dynamique, IPSL, CNRS, École Polytechnique, Université Paris-Saclay, 91128, Palaiseau, France
2Laboratoire de Météorologie Dynamique, IPSL, CNRS, UPMC Université Paris 06, Sorbonne Universités, 75252, Paris, France
3Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, USA
4National Oceanic and Atmospheric Administration, Earth System Research Laboratory, NOAA/ESRL, Boulder, Colorado, USA
5Institute for Atmospheric and Environmental Sciences, University of Frankfurt, Frankfurt, Germany
Abstract. An original and innovative sampling system called AirCore was presented by NOAA in 2010 (Karion et al., 2010). It consists of a long (>  100 m) and narrow (<  1 cm) stainless steel tube that can retain a profile of atmospheric air. The captured air sample has then to be analyzed with a gas analyzer for trace mole fraction. In this study, we introduce a new AirCore aiming to improve resolution along the vertical with the objectives to (i) better capture the vertical distribution of CO2 and CH4, (ii) provide a tool to compare AirCores and validate the estimated vertical resolution achieved by AirCores. This (high-resolution) AirCore-HR consists of a 300 m tube, combining 200 m of 0.125 in. (3.175 mm) tube and a 100 m of 0.25 in. (6.35 mm) tube. This new configuration allows us to achieve a vertical resolution of 300 m up to 15 km and better than 500 m up to 22 km (if analysis of the retained sample is performed within 3 h). The AirCore-HR was flown for the first time during the annual StratoScience campaign from CNES in August 2014 from Timmins (Ontario, Canada). High-resolution vertical profiles of CO2 and CH4 up to 25 km were successfully retrieved. These profiles revealed well-defined transport structures in the troposphere (also seen in CAMS-ECMWF high-resolution forecasts of CO2 and CH4 profiles) and captured the decrease of CO2 and CH4 in the stratosphere. The multi-instrument gondola also carried two other low-resolution AirCore-GUF that allowed us to perform direct comparisons and study the underlying processing method used to convert the sample of air to greenhouse gases vertical profiles. In particular, degrading the AirCore-HR derived profiles to the low resolution of AirCore-GUF yields an excellent match between both sets of CH4 profiles and shows a good consistency in terms of vertical structures. This fully validates the theoretical vertical resolution achievable by AirCores. Concerning CO2 although a good agreement is found in terms of vertical structure, the comparison between the various AirCores yields a large and variable bias (up to almost 3 ppm in some parts of the profiles). The reasons of this bias, possibly related to the drying agent used to dry the air, are still being investigated. Finally, the uncertainties associated with the measurements are assessed, yielding an average uncertainty below 3 ppb for CH4 and 0.25 ppm for CO2 with the major source of uncertainty coming from the potential loss of air sample on the ground and the choice of the starting and ending point of the collected air sample inside the tube. In an ideal case where the sample would be fully retained, it would be possible to know precisely the pressure at which air was sampled last and thus to improve the overall uncertainty to about 0.1 ppm for CO2 and 2 ppb for CH4.

Citation: Membrive, O., Crevoisier, C., Sweeney, C., Danis, F., Hertzog, A., Engel, A., Bönisch, H., and Picon, L.: AirCore-HR: a high-resolution column sampling to enhance the vertical description of CH4 and CO2, Atmos. Meas. Tech., 10, 2163-2181, https://doi.org/10.5194/amt-10-2163-2017, 2017.
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Short summary
A new high-resolution AirCore system is presented. This system flown with stratospheric balloons allows us to sample atmospheric air during the descent. The analysis of trace gases (CO2 and CH4 in this case) in the collected air sample provides information on the vertical distribution along the atmospheric column. The continuous vertical profiles retrieved may contribute to several research topics concerning the observation of greenhouse gases and, more generally, carbon cycle studies.
A new high-resolution AirCore system is presented. This system flown with stratospheric balloons...
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