AirCore: An Innovative Atmospheric Sampling System

Abstract

This work describes the AirCore, a simple and innovative atmospheric sampling system. The AirCore used in this study is 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; for the testing done in this work it was shaped into a 0.75-m-diameter coil. Measurements of CO2 and CH4 mole fractions in laboratory tests indicate a repeatability and lack of bias to better than 0.07 ppm (one sigma) for CO2 and 0.4 ppb for CH4 under various conditions. Comparisons of AirCore data with flask data from aircraft flights indicate a standard deviation of differences of 0.3 ppm and 5 ppb for CO2 and CH4, respectively, with no apparent bias. Accounting for longitudinal mixing, the expected measurement resolution for CO2 is 110 m at sea level, 260 m at 8000 m, and 1500 m at 20 000 m ASL after 3 h of storage, decreasing to 170, 390, and 2300 m, after 12 h. Validation tests confirm that the AirCore is a robust sampling device for many species on a variety of platforms, including balloons, unmanned aerial vehicles (UAVs), and aircraft.