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Open questions about the atmospheric hydrogen cycle

Open questions about the atmospheric hydrogen cycle. Thomas Röckmann Utrecht University The Netherlands. Overview. Introduction The global budget of H 2 Isotope information A new top-down approach Open questions and research needs. What do we want to understand?.

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Open questions about the atmospheric hydrogen cycle

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  1. Open questions about the atmospheric hydrogen cycle Thomas Röckmann Utrecht University The Netherlands

  2. Overview Introduction The global budget of H2 Isotope information A new top-down approach Open questions and research needs

  3. What do we want to understand? A forum to discuss the European research strategy concerning the environmental impacts of a future hydrogen economy

  4. Risks in the stratosphere H2 produces H2O in the stratosphere H2O forms polar stratospheric clouds PSCs necessary ingredient for O3 hole Tromp et al., 2003, 10-12% leak rate Warwick et al., 5% leak rate and feedbacks

  5. Chances in the troposphere • Substitution of CO2 by H2 will • reduce CO2 emissions • reduce particle emissions • reduce SOx emissions • reduce CO and NOx emissions • Effects on tropospheric ozone Schultz et al., 2003

  6. But also some risks Higher H2 levels expected due to leakage NOx reduction will lead to decrease in OH

  7. Potential impact Of H economy on H2 budget

  8. Atmospheric observations data from [Novelli et al., 1999] (until 1997) and Paul Novelli, personal communication).

  9. CMDL vs AGAGE

  10. AGAGE NH vs. SH

  11. Global budget/Sources and sinks of H2 after [Novelli et al., 1999]

  12. Bottom-up approach (Novelli et al., 1999) H2 from CH4: NMHC: (sum over all compounds): Fossil fuel combustion: Biomass burning:

  13. Sinks: OH: Soils: Sanderson et al.

  14. All sources/sinks have error bars >30% after [Novelli et al., 1999]

  15. Additional information from isotope measurements? data from [Gerst and Quay, 2000; 2001; Rahn et al., 2002a; 2002b; Röckmann et al, 2002]

  16. Top-down approach Near-tropopause samples (CARIBIC project) “The overwhelming role of soils in the global atmospheric hydrogen cycle“ T. S. Rhee, C. A. M. Brenninkmeijer and T. Röckmann, Atmos. Chem. Phys. Discuss., 5, 11215–11248, 2005.

  17. H2 concentrations Comparison to surface data

  18. Seasonal cycles: Mixing ratios and isotopes

  19. Isotope fractionation constants NH: sink dominated

  20. Relative sink strengths NH soil sink fraction is 877% NH OH sink: 9.4 1.3 Tg/yr NH soil sink: 62  10 Tg/yr

  21. SH soil sink Use effective soil area including snow cover extent

  22. What controls SH seasonality Sink effect does NOT dominate Transport from the NH during SH winter (movement of ITCZ and monsoon) Isotope information: Not so much biomass burning??? Photochemistry

  23. Results for individual sources

  24. Information on dD from biomass burning Data points from Gerst and Quay (pine needles and branches)

  25. dD map from: IAEA

  26. Results for individual sources

  27. Global average NH source Very close to 10‰from Rayleigh approach Confirmation that NH is sink dominated Calculate NH average source signature (include strat-trop exchange) DQ-NH~5‰

  28. Atmospheric budget and lifetime of H2 The overwhelming role of soils in the global atmospheric hydrogen cycle T. S. Rhee, C. A. M. Brenninkmeijer and T. Röckmann, Atmos. Chem. Phys. Discuss., 5, 11215–11248, 2005.

  29. Box model results SH green NH red Rahn and Horowitz, unpublished results

  30. Comparison to data

  31. Open questions about the atmospheric hydrogen cycle Can we understand spatial/temporal variability of H2? Is there a long-term trend? What are the strengths of sources/sinks? What is the role/mechanism of the soil sink? How will it change in a changing climate?

  32. Research needs • More information on soil sink (Randerson model) • Latitude, temperature, etc. dependence • Independent top-down approaches • Reliable H2/CO emission ratios from ff • Determination of seasonal isotope cycles at stations in the SH, tropics, NH • Source/sink isotope signatures (NMHC, CH4, HCHO photolysis, bb, ff, soils) • Better incorporation of measurements into global/regional models

  33. Thanks to Tae Siek Rhee Carl Brenninkmeijer Thom Rahn John Mak Peter van Velthoven Paul Novelli

  34. H2-concentration measurement with IRMS system

  35. Schematic view of the system

  36. Global budget/Sources and sinks of H2 Langenfelds et al., 2003 Novelli et al., 1999

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