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Natural and Anthropogenic Impacts on the Stable Isotopes of Oxygen of Ice-Core NO 3 −

Natural and Anthropogenic Impacts on the Stable Isotopes of Oxygen of Ice-Core NO 3 −. Wendell Walters & Greg Michalski December 10, 2013 AGU Fall Meeting 2013. Overview of Study . NO 3 − stable isotopes serve as proxies: Oxygen: atmosphere’s oxidation capacity

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Natural and Anthropogenic Impacts on the Stable Isotopes of Oxygen of Ice-Core NO 3 −

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  1. Natural and Anthropogenic Impacts on the Stable Isotopes of Oxygen of Ice-Core NO3− Wendell Walters & Greg Michalski December 10, 2013 AGU Fall Meeting 2013

  2. Overview of Study • NO3− stable isotopes serve as proxies: • Oxygen:atmosphere’s oxidation capacity • Determine changes in oxidation capacity following: • Explosive volcanic eruptions • Natural climate change • Anthropogenic Inputs • Few studies for time periods prior to 1800’s • Preliminary data indicates shift in modern oxidation capacity

  3. Outline • Background - Stable Isotopes - Using O isotopes of NO3− as proxy for oxidation capacity • Method - RIDS 95A Ice Core - Extraction & analysis method • Results - δ18O & Δ17O Data - Comparison to other studies • Summary • Future Work

  4. Stable Isotopes • Anharmonic Oscillator • Ratio of isotopes in natural samples can vary • Fractionate • Driven by differences in mass • Delta Notation: • δ(‰)isotopeX = [(Rsample/Rstandard) – 1]•1000 • Where R = heavyX/lightX

  5. ∆17O – Mass Independent Fractionation (MIF) • Oxygen has 3 stable isotopes: • 16O,17O, & 18O • Mass dependent fractionation: δ17O = 0.52•δ18O Figure Adapted from Michalski et al. 2011 • Notable exception is formation of O3 • MIF Measurement: Δ17O = δ17O − 0.52•δ18O • Δ17O transferred in O3 oxidation reactions

  6. ∆17O in Atmospheric NO3− NOx Polar Sources: Stratosphere Snowpack Continental

  7. ∆17O in Atmospheric NO3− NOx Polar Sources: Stratosphere Snowpack Continental R1: XONO2 + H2O → HNO3; Δ17O ≈ 40‰

  8. ∆17O in Atmospheric NO3− NOx Polar Sources: Stratosphere Snowpack Continental R1: XONO2 + H2O → HNO3; Δ17O ≈ 40‰ R2: NO2 + OH → HNO3; Δ17O ≈ 20‰

  9. ∆17O in Atmospheric NO3− NOx Polar Sources: Stratosphere Snowpack Continental R1: XONO2 + H2O → HNO3; Δ17O ≈ 40‰ R2: NO2 + OH → HNO3; Δ17O ≈ 20‰

  10. ∆17O in Atmospheric NO3− NOx Polar Sources: Stratosphere Snowpack Continental R1: XONO2 + H2O → HNO3; Δ17O ≈ 40‰ R2: NO2 + OH → HNO3; Δ17O ≈ 20‰ R3: NO3 + NO2↔ N2O5 + H2Osurface→ 2HNO3; Δ17O ≈ 35‰

  11. ∆17O in Atmospheric NO3− NOx Polar Sources: Stratosphere Snowpack Continental R1: XONO2 + H2O → HNO3; Δ17O ≈ 40‰ R2: NO2 + OH → HNO3; Δ17O ≈ 20‰ R3: NO3 + NO2↔ N2O5 + H2Osurface→ 2HNO3; Δ17O ≈ 35‰ R4: NO3 + VOC → HNO3; Δ17O ≈ 38‰

  12. ∆17O(NO3−) Previous Measurements David Mase: “Using Computer Models of Stable Isotope Abundance to Trace and Understand NOx Transfer to HNO3” Thursday 1:40 – 6:30pm Hall A-C (Moscone South) Midwest NO3 Rainwater Study • NO2+ OH → HNO3; Δ17O ≈ 20‰ • NO3 + NO2 ↔ N2O5 + H2Osurface→ 2HNO3; ∆17O ≈ 35‰ • NO3+ VOC → HNO3; Δ17O ≈ 38‰

  13. RIDS Ice Core • Sampling site located at 78°44'S, 116°20'W • 148-meter core • Dated from 1506-1995 • Broken into 1 meter subsections representing 2-3 year resolution RIDS 95A Mayewski, Paul A., Karl J. Kreutz, Mark Twickler, Sallie Whitlow, and Loren D. Meeker. 2005. Ross Ice Drainage System (RIDS) Glaciochemical Analysis. Boulder, CO: National Snow and Ice Data Center

  14. NO3− Extraction & Analysis Δ17O = δ17O − 0.52•δ18O

  15. Isotope Calibration Precision: δ18O ± 0.5‰ δ17O ± 0.6‰ Δ17O ± 0.8‰ Δ17O = δ17O − 0.52•δ18O

  16. δ18O (NO3−) Subject to fractionation: • Photolysis in snow-pack • HNO3(g) ↔ NO3−(aq) partitioning

  17. Δ17O (NO3−) Δ17Oavg ≈ 23‰ Post-depositional fractionation minimized in Δ17O (NO3−) (McCabe et al., 2005)

  18. Previous Δ17O (NO3−) Studies Δ17Oavg ≈ 31.5‰ Savarino et al., 2007. • Modern Δ17O (NO3−) much higher • Possibly related to: • Aerosol and heterogeneous chemistry • Halogen chemistry • Higher stratosphere nitrate contribution

  19. Previous Δ17O (NO3−) Studies Δ17O(NO3−) open squares Alexander et al., 2004. Measureable oxidation changes using Δ17O as a proxy

  20. Summary • Precise method for δ18O and Δ17O analysis of ice-core NO3− • Δ17O of NO3− proxy for measuring shifts in oxidation capacity • Oxidation capacity shift in southern hemisphere

  21. Future Work • Finish analyzing remaining RIDS cores • Δ17O transfer studies of NOx oxidation • Develop analytical methods to increase resolution for future ice core studies

  22. Acknowledgements Advisor: Dr. Greg Michalski Lab Manager: Dr. Bethany Theiling Lab Mates: • Dr. KrystinRiha • Dave Mase

  23. Questions? Wendell Walters Email: waltersw@purdue.edu Address: 550 Stadium Mall Drive 4169 Hampton Hall West Lafayette, IN 47907

  24. Supplementary • Mass Independent Fractionation in O3 O + O2→ O3* + M → O3 + M* • Asymmetric O3* has a longer lifetime • Heidenreich and Thiemens 1983 • Morton et al. 1990

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