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D 17 O Sulfate as a Proxy for Paleo Atmospheric Chemistry: Getting it Right at the Poles

D 17 O Sulfate as a Proxy for Paleo Atmospheric Chemistry: Getting it Right at the Poles. Becky Alexander Harvard University Telluride Atmospheric Chemistry Workshop August 10, 2004. Source: National Ice Core Laboratory. Source: National Ice Core Laboratory. Overview.

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D 17 O Sulfate as a Proxy for Paleo Atmospheric Chemistry: Getting it Right at the Poles

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  1. D17O Sulfate as a Proxy for Paleo Atmospheric Chemistry: Getting it Right at the Poles Becky Alexander Harvard University Telluride Atmospheric Chemistry Workshop August 10, 2004 Source: National Ice Core Laboratory

  2. Source: National Ice Core Laboratory Overview  D17O sulfate and the oxidation efficiency of the atmosphere  Vostok D17O sulfate climate record  Global model simulations using D17O sulfate tracer  Importance of alkalinity in rates of chemical transformation, climate, and D17O simulation  Polar perspective: How are we doing? Where are we going? From L. Barrie

  3. Oxidizing Power of the Atmosphere Climate change ? OH hn, H2O Primary Emissions DMS, SO2, CH4, … Secondary Species CO2, H2SO4, O3, … Primary Species H S, SO , CH , CO, 2 2 4 DMS, CO , NO, N O, 2 2 particulates Continental Biomass Marine Volcanoes Biogenics burning Biogenics

  4. Current knowledge of the past oxidative capacity of the atmosphere 60 Summit 6 50 40 4 O3 (ppb) H2O2 (mM) 30 2 20 Sigg & Neftel, 1991 10 0 0 1750 1850 1950 2000 1800 1900 1870 1890 1910 1930 1950 1970 1990 Year AD Measurements H2O2 O3 Year AD

  5. Ice Age Relative to preindustrial Holocene Industrial Era Relative to preindustrial Holocene Model Estimates of Past OH and O3 O3 OH Martinerie et al., 1995 Karol et al., 1995 Thompson et al., 1993

  6. Stable Isotope Measurements: Tracers of source strengths and/or chemical processing of atmospheric constituents (‰) = [(Rsample/Rstandard) – 1]  1000 R = minorX/majorX 18O: R = 18O/16O 17O: R = 17O/16O Standard = SMOW (Standard Mean Ocean Water) (CO2, CO, H2O, O2, O3, SO42-….) d17O/d18O 0.5 D17O =d17O– 0.5*d18O = 0

  7. Mass-Independent Fractionation +D17O -D17O D17O=d17O– 0.5*d18O 0 O + O2 O3* Mass-dependent fractionation line: d17O/d18O  0.5 Thiemens and Heidenreich, 1983 d17O/d18O 1

  8. Source ofD17OSulfate Aqueous Gas SO2 in isotopic equilibrium with H2O : D17Oof SO2 = 0 ‰ 1) SO32-+ O3 (D17O=35‰) SO42-D17O = 8.75 ‰ 2) HSO3-+ H2O2(D17O=1.7‰) SO42-D17O= 0.85 ‰ 3) SO2 + OH(D17O=0‰) SO42-D17O= 0 ‰ D17Oof SO42- a function relative amounts of OH, H2O2, and O3 oxidation Savarino et al., 2000

  9. Gas versus Aqueous-Phase Oxidation SO42- H2O2 CCN SO2 OH H2SO4 New particle formation OH NO3 Light scattering DMS Phytoplankton

  10. Vostok Ice Core D17O nssSO42- D17O (‰) DTs DTs data: Kuffey and Vimeux, 2001, Vimeux et al., 2002 Alexander et al., 2002

  11. Climate Variations in the Oxidation Pathways of Sulfate Formation DTs % OH Age (kyr) OH (gas-phase) oxidation greater in glacial period compared to interglacial

  12. Vostok sulfate explanation CCN H2SO4 SO42- OH O3 Transport SO2 Wet and dry deposition OH NO3 DMS Antarctica Ocean

  13. GEOS-CHEM http://www-as.harvard.edu/chemistry/trop/geos/index.html • Global 3-D model of atmospheric chemistry • Driven by assimilated meteorology (1987 –present). • 4ºx5º horizontal resolution • Includes aqueous and gas phase chemistry: • S(IV) + OH (gas-phase) • S(IV) + O3/H2O2 (in-cloud, pH=4.5) • Off-line sulfur chemistry (uses monthly mean OH and O3 fields from a full chemistry, coupled aerosol simulation)

  14. D17O of oxidants Tropospheric D17O values O3: 35‰ H2O2: 1.7‰ OH: 0‰ Photochemical Box Model Lyons, GRL, 2001 60 50 O3 40 Altitude (km) 30 HO2 20 OH Measured O3 Tropopause 10 10 20 0 30 40 50 60 Rainwater H2O2 HO2+HO2H2O2+O2 D17OSMOW (‰)

  15. D17O sulfate: GEOS-CHEM and measurements Whiteface Mtn, NY fogwater 0.3 ‰ Davis, CA fogwater 4.3 ‰ Site A, Greenland ice core 0.5-3‰ La Jolla aerosol 0.2-1.4‰ White Mtn, CA aerosol 1-1.7‰ La Jolla rainwater 1.1 ‰ INDOEX aerosol 0.5-3‰ Desert dust traps 0.3-3.5‰ South Pole aerosol 0.8-2‰ Vostok & Dome C ice cores 1.3-4.8‰ 0.0‰ 2.3‰ 4.6‰ January 2001 July 2001 Missing O3 oxidation source

  16. Sea-salt aerosols and atmospheric chemistry SO42- H2O2, O3 O3 Sea-salt aerosol CCN SO2 OH H2SO4 New particle formation OH NO3 Light scattering DMS Phytoplankton

  17. pH dependency of O3 oxidation and its effect on D17O of SO42- H2O2 H2O2 O3 O3 Sea-spray Lee et al., 2001

  18. OH• Acids: H2SO4(g) HNO3(g) RCOOH(g) SO2(g)  SO42- ? Na+, Cl-, CO32- pH=8 CO2(g) Alkalinity in the Marine Boundary Layer

  19. Subsidence other aerosols (acid or neutral) NH3(g) RCOOH(g) HNO3(g) Sea-salt aerosol CO32- O3 Deposition CO2(g) Emission GEOS-CHEM Sea-salt Alkalinity http://www-as.harvard.edu/chemistry/trop/geos/index.html Free troposphere Marine Boundary Layer Subsidence Cloud SO42- H2O2 H2SO4(g) OH SO2 OH NO3 DMS Emission

  20. INDOEX cruises – D17O sulfate Pre-INDOEX Jan. 1997 INDOEX March 1998

  21. Pre-INDOEX Cruise January 1997 ITCZ Alexander et al., 2004, manuscript in preparation

  22. INDOEX Cruise March 1998 ITCZ Alexander et al., 2004, manuscript in preparation

  23. Effect of sea-salt chemistry on SO2 and sulfate concentrations Percent (%) change (yearly average): - Case1 Case2 ´ | 100 | Case1 60°N SO2 60°S 60°N SO42- 60°S 180°W 180°E Alexander et al., 2004, manuscript in preparation

  24. Effect of sea-salt chemistry on gas-phase sulfate production rates 0% 100% 50% Mar/Apr/May Jun/Jul/Aug Sep/Oct/Nov Dec/Jan/Feb Alexander et al., 2004, manuscript in preparation

  25. Southern Hemisphere Perspective Vostok (PIH) 3‰ Alexander et al., 2002 South Pole aerosols 0.8-2‰ Michalski, Alexander and Thiemens, unpublished data

  26. Northern Hemisphere Perspective Site A (1930-1980) 1.9‰ Alert 1.0‰ Alexander et al., 2004 McCabe and Thiemens, unpublished data

  27. Arctic Measurements Alert (82°N, 85°W) Measurements GEOS-CHEM Measurements: Justin McCabe, UCSD, personal communication

  28. ?? Mn2+, Fe3+ SIV + ½ O2 SVI D17O = 0‰ Arctic Night-time Chemistry From Sirois and Barrie, 1999 xV (ng m-3) xMn (ng m-3)

  29. Conclusions Increased (30-80% range) gas-phase formed sulfate during the glacial period  positive climate feedback?  Change in OH/O3 concentrations? D17O shows importance of alkalinity in determining rates of reactions  implications for climate effect of sulfate aerosols Alert: Night time chemistry?

  30. Future Directions This is just the beginning! Higher resolution data over various timescales  WAISCORES Other sources of alkalinity Source: www.nasa.gov Paleoclimate global model simulations using oxygen isotope tracers: interpret and quantify existing data sets direct future measurement sites

  31. Acknowledgements Daniel Jacob Rokjin Park Bob Yantosca Qinbin Li Mark Thiemens Justin McCabe Greg Michalski Charles Lee Karl Kreutz Joël Savarino Robert Delmas

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