Development of stratospheric whole air sampling system using LHe as a cryogen and its operation results for 15 years Original Research Article

The paper describes a balloon-borne cryogenic whole air sampler and some results in the stratosphere. The sampler can collect more than 20 liters STP of stratospheric air at 12 different altitudes, which range from 10 to 35 km. Such capability offers sufficient air for analysis of minor constituents and isotope ratios as well as for storage of air for future analysis. An important feature of the system is to use liquid helium as a cryogen because of its availability. It is, however, not easy to utilize its cooling capacity effectively compared to other cryogens such as liquid neon. The difficulty lies in the specific characteristic of liquid helium; that is small latent heat and large sensible heat. Some of the other details described here includes thermal design of the cryogenic system, a reliable onboard computer system for controlling the cryogen and the air sampling operation. The sampler has been used for more than 15 years without any major modification. Sampling performance of the system during 22 flights conducted since 1985 is also presented.