The transport of water vapor near the tropopause and lower stratosphere, e.g. The inflow of tropospheric water vapor into the stratosphere and the vertical redistribution of stratospheric water vapor due to sedimentation of Polar Stratospheric Cloud (PSC) particles was investigated. In situ collection of up to six water vapor samples from flights operating between Christchurch and McMurdo were ... collected. During flight, the water vapor of 1-10m3 ambient air is frozen out by an liquid nitrogen cooled cold trap resulting in sample sizes of 0.05-0.5 g water each. The isotopic ratios D/H, T/H and 18O/16O of the water samples were measured. Due to very low stratospheric temperatures over Antarctica, water vapor forms condensates (PSC). Its on the surface of these particles where chemical processes can transform inactive halogen bearing species into active species leading to massive ozone destruction in early spring. Due to their mass, the PSC particles can descend in the earth's gravitational field, leading to a dehydration and denitrification of the polar vortex. Due to the low mixing ratios of water in the lower stratosphere, the errors associated with direct measurements of water vapour are too high to find evidence for dehydration and instead isotopic methods measuring rare hydrogen isotopes 2H (deuterium) and 3H (tritium) along with stable oxygen isotope measurements was used to find evidence of dehydration and therefore links between PSC cloud sedimentation and ozone chemistry.