Development of a balloon-borne stratospheric air sampler.

为了弄清平流层中温室气体的分布和变化，有必要研制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氖气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原型，并使用三种冷冻头进行了空气采样实验。结果表明：经150 ~ 240秒氖气注入后，低温头温度降至氖的液化点（27K）。空气样本的压力设定为25至200 hPa，由采样系统以每分钟0.4至1.2标准升的速率低温收集。当样品压力为25 hPa和200 hPa时，收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呈现出不同的模式。当样品压力低于60 hPa时，空气采样至少持续10分钟。另一方面，对于120 hPa以上的空气样品，在开始采样后约3分钟，空气采样终止。造成这种差异的原因似乎是冷冻头的一部分温度高于空气样品的氧气熔点（120 hPa以上）。为了获得更多的空气样品，应对冷冻头进行进一步的修改。

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.