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  author = {{Membrive}, O. and {Crevoisier}, C. and {Sweeney}, C. and {Danis}, F. and 
	{Hertzog}, A. and {Engel}, A. and {B{\"o}nisch}, H. and {Picon}, L.
  title = {{AirCore-HR: a high-resolution column sampling to enhance the vertical description of CH$_{4}$ and CO$_{2}$}},
  journal = {Atmospheric Measurement Techniques},
  year = 2017,
  month = jun,
  volume = 10,
  pages = {2163-2181},
  abstract = {{An original and innovative sampling system called AirCore was presented
by NOAA in 2010 Karion et al.(2010). It consists of a long ( $\gt$ 100 m)
and narrow ( $\lt$ 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
CO$_{2}$ and CH$_{4}$, (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 CO$_{2}$ and CH$_{4}$ 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 CO$_{2}$ and CH$_{4}$ profiles) and captured
the decrease of CO$_{2}$ and CH$_{4}$ 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 CH$_{4}$ profiles and
shows a good consistency in terms of vertical structures. This fully
validates the theoretical vertical resolution achievable by AirCores.
Concerning CO$_{2}$ 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 CH$_{4}$ and 0.25 ppm for
CO$_{2}$ 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
CO$_{2}$ and 2 ppb for CH$_{4}$.
  doi = {10.5194/amt-10-2163-2017},
  adsurl = {https://ui.adsabs.harvard.edu/abs/2017AMT....10.2163M},
  adsnote = {Provided by the SAO/NASA Astrophysics Data System}