Atmos. Chem. Phys. Discuss., 11, 5811-5866, 2011
www.atmos-chem-phys-discuss.net/11/5811/2011/
doi:10.5194/acpd-11-5811-2011
© Author(s) 2011. This work is distributed
under the Creative Commons Attribution 3.0 License.
Review Status
This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Global modelling of H2 mixing ratios and isotopic compositions with the TM5 model
G. Pieterse1, M. C. Krol1,2, A. M. Batenburg1, L. P. Steele3, P. B. Krummel3, R. L. Langenfelds3, and T. Röckmann1
1Institute for Marine and Atmospheric Research Utrecht (IMAU), Utrecht, The Netherlands
2Department of Meteorology and Air Quality at Wageningen University, Wageningen, The Netherlands
3Centre for Australian Weather and Climate Research, CSIRO Marine and Atmospheric Research, Australia

Abstract. The isotopic composition of molecular hydrogen (H2) contains independent information for constraining the global H2 budget. To explore this, we have implemented hydrogen sources and sinks, including their isotopic composition, into the global chemistry transport model TM5. For the first time, a global model now includes a simplified but explicit isotope reaction scheme for the photochemical production of H2. We present a comparison of modelled results for the H2 mixing ratio and isotope composition with available measurements on the seasonal to inter annual time scales for the years 2001–2007. The base model results agree well with observations for H2 mixing ratios. For δD[H2], modelled values are slightly lower than measurements. A detailed sensitivity study is performed to identify the most important parameters for modelling the isotopic composition of H2. The results show that on the global scale, the discrepancy between model and measurements can be closed by adjusting the default values of the isotope effects in deposition, photochemistry and the stratosphere-troposphere exchange within the known range of uncertainty. However, the available isotope data do not provide sufficient information to uniquely constrain the global isotope budget. Therefore, additional studies focussing on the isotopic composition near the tropopause and on the isotope effects in the photochemistry and deposition are recommended.

Citation: Pieterse, G., Krol, M. C., Batenburg, A. M., Steele, L. P., Krummel, P. B., Langenfelds, R. L., and Röckmann, T.: Global modelling of H2 mixing ratios and isotopic compositions with the TM5 model, Atmos. Chem. Phys. Discuss., 11, 5811-5866, doi:10.5194/acpd-11-5811-2011, 2011.
 
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