Séminaire

Colm Sweeney vient nous rendre une petite visite au LMD-X ce vendredi et en profitera pour donner un séminaire sur un nouveau système de mesure de profils (0-25km) de gaz à effet de serre : l'AirCore.

One of the primary focus of NOAA/ESRL/GMD Carbon Cycle Group is on vertical profiles of greenhouse gas measurements over North America. This program is dedicated to understanding both the transport and surface processes that determine greenhouse gas concentrations throughout the free troposphere. Regular flights from numerous sites across North America, as well as targeted, intensive sampling missions, have provided valuable important validation points for models and given new insights into large-scale transport of atmospheric air masses.

Among the new tools and platforms designed for collecting vertical profiles of CO2 and other trace gases, the AirCore is a simple and innovative atmospheric sampling system. It is based on a 150-m long stainless steel tube, open at one end and closed at the other, that relies on positive changes in ambient pressure for passive sampling of the atmosphere. The AirCore evacuates while ascending to a high altitude and collects a sample of the ambient air as it descends. It is sealed upon recovery and measured with a continuous analyzer for trace gas mole fraction. The AirCore tubing can be shaped into a variety of configurations to accommodate any sampling platform. Measurements of CO2 and CH4 mole fractions in laboratory tests indicate a repeatability and accuracy of better than 0.05 ppm for CO2 and 0.4 ppb for CH4 under a variety of conditions. Comparisons of AirCore data with continuous in situ and flask data in aircraft field tests indicate average absolute differences of 0.3 ppm and 5 ppb for CO2 and CH4, respectively, with no apparent bias. Accounting for molecular diffusion and flow-induced mixing, the expected measurement resolution for CO2 and CH4 is 110 m at sea level and 260 m at 8000 masl after three hours of storage, decreasing to 170 m and 400 m, respectively, after 9 hours. Validation tests confirm that the AirCore is a robust sampling device for many species on a variety of platforms including balloons, UAVs, and aircraft.

Thibaud Thonat

thibaud.thonat@lmd.polytechnique.fr