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Water isotopes in the atmosphere

Water isotopes in the atmosphere. Arno de Lange 22 November 2006 Werkbespreking. Science with TELIS. Ozone chemistry Stratospheric water Transport UTLS ( U pper T roposphere L ower S tratosphere) HNO 3 and NAT ( N itric A cid T rihydrate = HNO 3 ·3 H 2 O)

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Water isotopes in the atmosphere

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  1. Water isotopes in the atmosphere Arno de Lange 22 November 2006 Werkbespreking

  2. Science with TELIS Ozone chemistry Stratospheric water Transport UTLS (Upper Troposphere Lower Stratosphere) HNO3 and NAT (Nitric Acid Trihydrate = HNO3·3 H2O) Central questions pertaining to stratospheric water: • What is the origin of stratospheric water? • Does the amount of stratospheric water increase? • If so, why? Werkbespreking, 22 November 2006

  3. How to get insight? Water dynamics Phase transitions H2O (g)  H2O (s) Chemical reactions CH4 + OH  CH3 + H2O Transport • Different rates for different isotopes • Measuring enrichment/depletion gives insight in the different processes Werkbespreking, 22 November 2006

  4. What is an isotope again? Werkbespreking, 22 November 2006

  5. Chemical bonding Hydrogen Oxygen H2O Hydrogen Chemical bonding is determined by electronic configuration Chemical reactions are governed by electronic configuration Werkbespreking, 22 November 2006

  6. Mass matters • Kinetic energy kT = ½ mv2 • Heavier isotopes have lower diffusion velocity • Heavier isotopes have a lower collision frequency  lower reaction rate • Binding energy Zero point energy for heavier isotopes is lower • HDO and H218O have lower vapor pressures than H216O Werkbespreking, 22 November 2006

  7. Isotope ratios and concentration Isotope (abundance) ratio R = abundance of rare isotope / abundance of abundant isotope For instance RHDO = [HDO] / [H216O]  3  10-4 Enrichment d = R/Rref – 1 ( 1000 ‰) For instance Rref = 3.0  10-4 RHDO = 2.9  10-4 d = 2.9/3.0 – 1 = –33 ‰ Werkbespreking, 22 November 2006

  8. Standard Mean Ocean Water Early references Average ocean water and melted snow Refined in 60s by US National Bureau of Standards SMOW (Standard Mean Ocean Water) However, the physical integrity of the U.S. standards soon came into question - Wikipedia Recalibrated reference (1967) by IAEA V-SMOW (Vienna Standard Mean Ocean Water) Werkbespreking, 22 November 2006

  9. Evaporation 1 HDO in vapor will be depleted by 78.4‰, because HDO is heavier than H2O Werkbespreking, 22 November 2006

  10. Evaporation 2 Higher temperature = more evaporation (both H2O and HDO) Increase with temperature in favour for HDO Werkbespreking, 22 November 2006

  11. Evaporation 3 • Latitude • Elevation • Distance to coast Average dD of precipitation in North America Werkbespreking, 22 November 2006

  12. Rainout effect • Water vapor is depleted with respect to ocean water • Rain is enriched with respect to atmospheric vapor • Vapor is depleted after rainfall • Vapor gets more depleted with every rainfall Werkbespreking, 22 November 2006

  13. Evaporation 4 Werkbespreking, 22 November 2006

  14. Global Meteoric Water Line GMWL: 2d=818d+10‰ Precipitation 1 1 2 2 3 3 Water vapor 1 1 2 2 3 3 Werkbespreking, 22 November 2006

  15. Evaporation Table is only valid for systems in equilibrium! Relative humidity > 95% slope ~8 Relative humidity < 25% slope ~4 Werkbespreking, 22 November 2006

  16. Deviations from GMWL Werkbespreking, 22 November 2006

  17. d17O vs. d18O Werkbespreking, 22 November 2006

  18. Stratospheric water Oxygen exchange Transport Dry stratosphere (1%) Ice lofting Graduate ascend Methane oxidation Influx from troposphere Humid troposphere (70%) Out flux into troposphere Werkbespreking, 22 November 2006

  19. Tropospheric water influx in tropics Aridity of stratosphere unexplained • Two mechanisms of dehydration • Ice lofting by convective processes (ice is produced in troposphere) • Gradual ascend of air parcels (ice is produced along the way) • Two different mechanisms = different isotopic signatures • Dehydration is function of tropopause temperature dD/d18O ratio in upper troposphere • Expectation: dD/d18O  8 • Measurement: dD/d18O  5 TELIS: • Check dD/d18O in upper troposphere/lower stratosphere • Check tape recorder effect of depletion Werkbespreking, 22 November 2006

  20. Tape recorder effect of H2O (non isotopic) Werkbespreking, 22 November 2006

  21. Water by oxidation Creation of water by oxidation of CH4 and H2 • Enriched in HDO with respect to tropospheric water • Oxidation mainly in upper stratosphere and mesosphere • Enters stratosphere mainly in polar regions TELIS: • Check if dD increases with altitude in polar region • Check HDO profile in polar summer (Thomas found an hitherto unexplained anomaly) Werkbespreking, 22 November 2006

  22. Oxygen exchange reactions Oxygen exchange reactions with O2, O3, HOx, NOx • Ozone anomaly may be transferred to water • > 99% of all oxygen atoms that end up in H2O stem from OH TELIS: • Check d17O/d18O to see if ozone anomaly is transferred Werkbespreking, 22 November 2006

  23. TELIS H218O Werkbespreking, 22 November 2006

  24. TELIS HDO Werkbespreking, 22 November 2006

  25. Conclusion • Isotopes in general can help to assess different processes • Stratospheric isotopic water measurements give insight in: • UTLS transport • Oxidation processes • Oxygen exchange mechanisms • TELIS can contribute to answer these questions, because: • dD gives if, and how much depletion occurs • dD vs. d18O (or d17O) gives insight in influx mechanism and methane oxidation • d17O vs. d18O gives insight in oxygen exchange mechanisms and ozone anomaly transfer Werkbespreking, 22 November 2006

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