Development of a balloon-borne stratospheric air sampler.

为了弄清温室气体在平流层中的分布和变化，有必要开发一种可与小气球一起使用的小而轻的空气采样系统。为此，我们研制了一种利用高压霓虹气体绝热膨胀的新型低温空气采样器。在本研究中，我们制作了采样器的样机，并用三种冷冻头进行了空气采样实验。实验结果表明：在150~240秒的时间内，低温头部的温度降到了霓气液化点(27K)。空气样本的压力设定为25至200百帕，由采样系统以每分钟0.4至1.2标准落叶的速率进行低温采集。当样品压力为25和200百帕时，采集的空气样品总量分别约为6.0和3.0标准升。质量流量计测量的采样率随样品压力的不同而呈现不同的规律。当样品压力低于60百帕时，空气采样持续至少10分钟。另一方面，对于120百帕以上的空气样本，空气采样在采样开始后约3分钟结束。造成这种差异的原因似乎是，对于120百帕以上的空气样品，部分冷冻头的温度高于氧气的熔点。为了获得更多的空气样品，需要对冷冻头进行进一步的改进。

In order to clarify distributions and variations of greenhouse gases in the stratosphere, it is necessary to develop a small and light weight air sampling system that can be used with a small balloon. For this purpose, we have developed a new cryogenic air sampler using adiabatic expansion of high pressure neon gas. In the present study, we produced prototypes of the sampler and performed air sampling experiments with three kinds of cryo-head. The results obtained are summarized as follows :It was confirmed that the temperature at the cryo-head decreased down to the liquefied point of neon (27K) after 150 to 240 seconds of neon gas introduction. Air sample, of which pressure was set to be from 25 to 200 hPa, was collected cryogenically by the sampling system at a rate from 0.4 to 1.2 standard litters per minute. Total amount of the collected air sample was about 6.0 and 3.0 standard liters when the sample pressures were 25 and 200 hPa, respectively.The sampling rate measured by a mass flow meter showed different patterns depending on the sample pressure. When the sample pressure was below 60 hPa, the air sampling continued at least 10 minutes. On the other hand, for the air sample above 120 hPa, the air sampling terminated about 3 minutes after the sampling started. The cause of the difference was seemed to be the fact that the temperature of a part of the cryo-head was above the melting point of oxygen for the air sample above 120 hPa. To obtain more amount of air sample, further modifications should be made for the cryo-head.