低温冷阱大气水汽收集技术及其在水稳定同位素研究中的应用

系统地介绍了低温冷阱大气水汽收集的基本原理、实验方法、实验过程中的误差估计以及该方法在水稳定同位素研究中的应用。基于低温条件下显著增加水汽凝结面和凝结时间的方法,使水汽完全凝结;利用水分在真空条件下升华/蒸发及其在低温条件下再凝结的原理,实现对水汽样品的转移收集。收集的水汽样品中稳定同位素值的误差主要来自两方面:(1)低温条件下玻璃冷阱中部分未冷凝的饱和水汽;(2)样品室温融化后,外界大气进入瓶内与融化后的水汽样品发生同位素平衡分馏;并分别对上述两种误差进行了理论估计。利用低温冷阱水汽收集和稳定同位素离线测试方法在以下三方面具有较重要的应用:(1)过量~(17)O是当前水稳定同位素研究的前沿,实现对大气水汽中过量~(17)O高精度测试是该方法的重要应用;(2)获取低水汽浓度地区高精度大气水汽稳定同位素测试数据;(3)验证激光光谱稳定同位素分析仪在线水汽稳定同位素测试数据。

Cold trap technique for collecting atmospheric water vapor and its applications in the study of water stable isotopes

This study systematically introduces the cold trap technique for use in the collection of atmospheric water vapor, including its basic principles, experimental methods, error estimates, and applications in the study of water stable isotopes. Atmospheric water vapor can condense completely in the cold trap by increasing both the condensation surface area (by filling with small glass beads) and the condensation time under conditions of cold temperature (?80℃). The condensed water sublimates or evaporates by heating the cold trap, and then the sublimated or evaporated water vapor re-condenses in a sample bottle under vacuum conditions and cold temperatures (?80℃). The error of the stable isotopic composition in the collected water vapor derives mainly from two aspects: the lost saturated vapor during collection and the ambient air in the bottle mixed with the sampled water. The magnitudes of the above two errors were estimated theoretically in the study. Water vapor collection using a cold trap has important applications in the study of water stable isotopes including achieving high-accuracy δ17O data in atmospheric water vapor, obtaining high-accuracy isotopic composition of atmospheric water vapor in the remote areas of polar ice sheets where vapor concentration is very low, and verifying the isotopic measurements of atmospheric water vapor by laser absorption spectrometers.