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UP: Umweltphysik
UP 12: Poster: Atmosph
ärische Spurengase und Aerosole: Instrumentelles
UP 12.4: Poster
Tuesday, March 14, 2006, 14:00–16:00, C
On the in situ measurement of H2O isotopic ratios in the UT/LS by means of diode laser spectroscopy — •Christoph Dyroff1, Andreas Zahn1, Peter Werle1,2, and Wolfgang Freude3 — 1Forschungszentrum Karlsruhe (IMK), Germany — 2CNR-National Institute for Applied Optics, Florence, Italy — 3Universität Karlsruhe (IHQ), Germany
Studies of the isentropic transport of water vapour into the lower stratosphere, and the vertical transport into the tropopause region (extratropics) or the tropical transition layer (TTL) will contribute to an improved understanding of the water vapour budget in the upper troposphere and in the lower stratosphere (UT/LS). This will help to assess the potential change of water vapour and its impact to the Earth’s radiation budget and climate change.[1]
H2O mixing ratios typically range between a few thousand parts per million by volume (ppmv) in the tropical troposphere to about 5 ppmv in much dryer lower stratospheric regions, giving rise to the need for a high dynamic range as well as very low detection limits of the order of 1× 10−6 fractional absorbance to assess even high δ D values around −70 %. Suitable spectral regions, ranging from the near-infrared to the mid-infrared, as well as the constraints of their selection are presented. An instrumental design along with calibration procedures for the in situ measurement of the isotopic ratios δ 18O, δ 17O, and δ D in water vapour by means of tunable diode laser spectroscopy is given, and preliminary laboratory results are discussed.
[1] A. Zahn, J. Atmos. Chem., 39, 303-325 (2001).