The Isotopic Composition of Water Vapor in the Upper Troposphere/Lower Stratosphere Region: Modeling, Analysis and Sampling

Abstract

The isotopic composition of water vapor in the upper troposphere/lower stratosphere:} Exact knowledge about the isotopic composition of water vapor in the tropopause region and the stratosphere provides important information for the understanding of atmospheric transport and photochemistry. The presented thesis describes with the help of models the processes governing the isotopic composition of atmospheric water vapor. The stable isotopologues - $HDO$, $H_2^{17}O$ and $H_2^{18}O$ - and the radioactive isotopologue $HTO$ are discussed. A complete analytical procedure has been developed for the purpose of precise measurements of the mentioned water isotopologues. For the stable isotopologues, it consists of three instruments: a continuous-flow system for the chemical decomposition of $H_2O$ to $H_2$ and $O_2$ for subsequent mass-spectrometrical analysis, a calibration unit for the production of water vapor with known isotopic composition, and a cryogenic sampling unit for operation aboard airplanes and balloons. The required sample amount could be reduced to about $100ng$. Further, experiments with a sampling unit for tritiated water vapor have been performed. With these apparatus, samples of atmospheric water vapor have been taken on 6 flights between New Zealand and Antarctica, and have later been analyzed in the laboratory.