Heidelberg 2015 – scientific programme

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UP: Fachverband Umweltphysik

UP 3: Meßtechnik

UP 3.5: Talk

Wednesday, March 25, 2015, 18:30–18:45, G/gHS

D/H Isotope Ratio Measurements of Atmospheric Volatile Organic Compounds — •Thomas Meisehen, Fred Bühler, Ralf Koppmann, and Marc Krebsbach — Institute for Atmospheric and Environmental Research, University of Wuppertal

Analysis of isotope ratios in volatile organic compounds (VOC) is a reliable method to allocate their sources, to estimate atmospheric residence times and investigate physical and chemical processes on various temporal and spatial scales. Most investigations yet focus on carbon isotope ratios. However, more detailed information can be gained by the ratio of deuterium (D) to hydrogen (H) in VOC, especially due to the high mass ratio.

We thoroughly set up and characterized a gas chromatograph pyrolysis isotope ratio mass spectrometer to measure the D/H ratios in atmospheric VOC. From about 200 L of air VOC were absorbed on Tenax^®TA to remove atmospheric CO₂. Our results show that the pyrolysis method has a significant impact on the D/H ratios. A pyrolysis temperature of at least 1723 K and conditioning of the ceramic tube on a regular basis is essential to obtain reproducible D/H isotope ratios. D/H ratios of the pure VOC used for a custom made gas standard mixture were determined independently by elemental analysis. Comparison of the results shows a good agreement. We further demonstrate the stability of our system and show that the sample preparation does not affect the isotope ratios. Combining measurements of carbon and hydrogen isotopes could lead to considerable improvement in our understanding of atmospheric processes in the future.