Development of a balloon-borne stratospheric air sampler.

为了弄清平流层温室气体的分布和变化规律，有必要研制一种小型、轻量、可与小型气球配合使用的大气采样系统。为此，我们研制了一种利用高压氖绝热膨胀的低温空气采样器。在本研究中，我们制作了采样器的原型，并进行了空气采样实验与三种冷冻头。得到的结果总结如下：据证实，在低温头的温度下降到氖的液化点（27 K）后，150至240秒的氖气引入。空气样品的压力设定为25 ~ 200 hPa，通过采样系统以0.4 ~ 1.2标准升/分钟的速率低温采集。当采样压力为25和200 hPa时，采集的空气样品总量分别为6.0和3.0标准升，用质量流量计测量的采样率随采样压力的不同而呈现不同的模式。当样品压力低于60 hPa时，空气取样持续至少10分钟。另一方面，对于120 hPa以上的空气样品，空气采样在采样开始后约3分钟终止。造成差异的原因似乎是这样一个事实，即低温头的一部分的温度高于120 hPa以上的空气样品的氧气熔点。为了获得更多的空气样品，需要对低温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.