•Volker Ebert¹, Holger Teichert¹, Carsten Giesemann¹, Harald Saathoff² und Ulrich Schurath^2
1Physikalisch-Chemisches Institut, Universität Heidelberg, Im Neuenheimer Feld 253, 69120 Heidelberg, volker.ebert@pci.uni-heidelberg.de
²Institut für Meteorologie und Klimaforschung, Forschungszentrum Karlsruhe, GmbH, 76021 Karlsruhe

A central parameter for the dynamics of atmospheric ice clouds is the time-dependent water super-saturation of the gasphase. Extractive measurement techniques can not directly detect this parameter due to their influence on the phase equilibrium between ice, liquid and solid H2O. Our new diod-laser-based in situ absorption spectrometer enables the selective, sampling-free and completely calibration-free detection of H2O-vapour in such cryogenic aerosols. A fiber-coupled diode laser in combination with an open 82m-White-cell and low temperature optics allowed a detection limit of 15ppb H2O (at p=1000-800mBar and a time resolution of 2s) by efficively avoiding disturbances by the high water content in the outside air. Using this device we recently successfully demonstrated during tests over several weeks in the aerosol chamber AIDA (at the Forschungszentrum Karlsruhe) at temperatures between 270 and 190K the first highly time resolved in situ detection of the dynamic H2O super saturation of the gasphase during ice particle formation processes in cryogenic aerosols.