Abstract:

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.

Key words: cold trap, water vapor collection, water vapor stable isotopes