The proposed sensor can be used to provide "ground truth" information for several NASA initiatives on measurements of greenhouse and related gases in the atmosphere, including OCO2/ASCENDS, AURA/TES, and the TCCON sites. We propose to develop an AirCore sensor which will be hoisted aloft on a helium weather balloon to a nominal altitude of 70,000 ft. When the balloon reaches its target altitude, the payload (glider UAV plus AirCore sampler) will be released. The UAV (known as the Retriever) will then follow a prescribed spiraling descent path during which time the AirCore sampler will collect a continuous atmospheric sample. Upon UAV recovery, the AirCore sample will be analyzed.