AirCore is an innovative high-altitude air sampling system that was first developed at NOAA in the USA. In principle, the AirCore consists of a long tubing in the shape of a coil, which is sealed at one end and open at the other. Deployed to a balloon, it rises up into the stratosphere to approximately 30 km. During ascent, the AirCore evacuates due to the decreasing ambient pressure. During descent the tube fills with ambient air and captures a continuous vertical profile. The length of the tubing and the laminar flow during sampling play a crucial role in preserving the continuous sample. The stratospheric air is stored near the sealed end of the AirCore, whereas the tropospheric air is stored near the open end.

Over time, the sampled air mixes due to molecular diffusion. Albeit, one can reconstruct the vertical profile if the AirCore sample is measured directly after landing. For analysis, we use a Picarro G2401 Cavity Ring-Down Spectrometer, which measures CO2, CH4, CO and water vapor in a continuous gas flow. The AirCore system of the Goethe University Frankfurt is described in detail in Engel et al., 2017. The total weight of our AirCore including the electronic system and the protective casing is approximately 2.5 kg – little enough to be deployed to small and economic weather balloons.

From AirCore measurements, we infer the mean age of air (link), a conceptual tool that provides information on time scales of stratospheric transport. We conducted AirCore measurements at the Meteorological Observatory Lindenberg, in Timmins in Canada and at the Sodankylä Geophysical Observatory in Finland. In order to investigate changes in stratospheric transport, regular AirCore measurements will allow us to monitor the long-term evolution of stratospheric mean age.