1.  17 O proxy for atmospheric chemistry: Towards model interpretation of the ice core record Becky Alexander NOAA Postdoctoral Fellow Harvard University March 25, 2005

2. Outline Atmospheric chemistry and the oxidation capacity of the atmosphere: climate ↔ chemistry Sulfate  17 O from the Vostok record GEOS-CHEM  17 O simulations Future plans Department of Atmospheric Sciences, University of Washington, Seattle

3. Secondary Species CO 2, H 2 SO 4, O 3, … Oxidizing Power of the Atmosphere Volcanoes Marine Biogenics Biomass burning Continental Biogenics Primary Species H 2 S, SO 2, CH 4, CO, DMS, CO 2, NO, N 2 O, particulates Climate change OH h  H 2 O Primary Emissions DMS, SO 2, CH 4, …

4. O3O3 OH Model Estimates of Past OH and O 3 Industrial Era Relative to preindustrial Holocene LGM Relative to preindustrial Holocene Karol et al., 1995 Thompson et al., 1993 Martinerie et al., 1995

5. Glacial/Interglacial CH 4 variations Kaplan, 2002 Wetland CH 4 emissions Present day LGM Wetland CH 4 emissions 24% less in LGM. Not enough to explain glacial/interglacial change (~50%) in atmospheric CH 4 concentrations.

6. The Vostok Ice Core Record: Aerosols SO 4 2- (ppb) [SO 4 2- ] tracks [MSA - ] suggesting a predominant DMS (oceanic biogenic) source (Legrand et al., 1991)  D (‰)  D from Jouzel et al., 1987 [SO 4 2- ] from M. Legrand

7. Sulfur Cycle in the Atmosphere Surface DMSCS 2 H2SH2S SO 2 SO 4 2- OH O 3, H 2 O 2 OH, NO 3 MSA OH

8. Radiative Forcing: Greenhouse Gases and Aerosols IPCC report, 2001

9. Effects of Aerosols on Climate Direct Effect Indirect Effect    Reflection Refraction Absorption Ramanathan et al., 2001 Aerosol number density (cm -3 ) Cloud droplet number density (cm -3 ) Great Smoky Mountains Visibility: 150 milesVisibility: 15 miles

10. New Particle Formation SO 2 + OH (+O 2 + H 2 O)  H 2 SO 4 (g) (+HO 2 ) CCN > ~ 0.1  m H2OH2O NH 3 ? H 2 SO 4 (g) Condensation RCOOH Activation Water vapor Updraft velocity Aerosol number density Size distribution Chemical composition From Boucher and Lohmann, 1995 nssSO 4 2- (mg m -3 ) CDNC (m -3 ) HSO 3 - + H 2 O 2 /O 3  SO 4 2-

11. SMOW Air O 2 Mass-Dependent Fractionation Mass-dependent fractionation line:  17 O/  18 O  0.5  17 O  18 O Basaltic and sedimentary rocks Rain and cloud water  17 O /  18 O  1 Mass-dependent fractionation line:  17 O/  18 O  0.5 O + O 2  O 3 * Thiemens and Heidenreich, 1983 Mass-Independent Fractionation  17 O  17 O  17 O =  17 O – 0.5 *  18 O  0

12. Source of  17 O Sulfate SO 2 in isotopic equilibrium with H 2 O :  17 O of SO 2 = 0 ‰ 1) SO 3 2- + O 3 (  17 O=35‰)  SO 4 2-  1 7 O = 8.8 ‰  17 O of SO 4 2- a function relative amounts of OH, H 2 O 2, and O 3 oxidation Savarino et al., 2000 3) SO 2 + OH (  17 O=0‰)  SO 4 2-  17 O = 0 ‰ 2) HSO 3 - + H 2 O 2 (  17 O=1.7‰)  SO 4 2-  17 O = 0.9 ‰ Aqueous Gas

13. Analytical Procedure SO 4 2- Ag 2 SO 4 Decontamination ConcentrateIon ChromatographIonic separation

14. Ag 2 SO 4  O 2 + SO 2 Removable quartz tube 1050°C magnet To vacuum GC SO 2 trap He flow Sample loop 5A mol.sieve vent SO 2 port O 2 port Analytical Procedure Isotope Ratio Mass Spectrometer

15. Vostok Ice Core  17 O nssSO 4 2-  T s data: Kuffey and Vimeux, 2001, Vimeux et al., 2002 Alexander et al., 2002  17 O (‰) TsTs

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

17. Antarctica Ocean DMS OHNO 3 SO 2 OH H 2 SO 4 O3O3 SO 4 2- Transport Wet and dry deposition Vostok sulfate explanation CCN

18. Sulfate Formation Pathways in GEOS-CHEM SO 2 H 2 SO 4 OH DMS OHNO 3 H 2 O 2, O 3 SO 4 2- pH = 4.5 Gas-phase Aqueous-phase Park et al., 2004 http://www-as.harvard.edu/chemistry/trop/geos/index.html

19. Lee et al., 2001 H2O2H2O2 O3O3 pH dependency of O 3 oxidation and its effect on  17 O of SO 4 2-

20. GEOS-CHEM  17 O Sulfate Simulation SO 2 + OH (gas-phase)  17 O=0‰ S(IV) + H 2 O 2 (in-cloud)  17 O=0.9‰ S(IV) + O 3 (in-cloud)  17 O=8.8‰ Assume constant, global  17 O value for oxidants  17 O ‰ methodreference O3O3 35 Photochemical model Lyons 2001 H2O2H2O2 1.3-2.2 (1.7) Rainwater measurements Savarino and Thiemens 1999 OH0 ExperimentalDubey et al., 1997

21.  17 O sulfate: GEOS-CHEM January 2001 July 2001 0.0‰2.3‰4.6‰ 0 2 4 6 8 01234  17 O sulfate (‰) H 2 O 2 (ppbv) HSO 3 -, H 2 O 2, O 3

22.  17 O sulfate: GEOS-CHEM and measurements January 2001July 2001 0.0‰2.3‰4.6‰ Davis, CA fogwater 4.3 ‰ Whiteface Mtn, NY fogwater 0.3 ‰ White Mtn, CA aerosol 1-1.7‰ La Jolla rainwater 1.1 ‰ La Jolla aerosol 0.2-1.4‰ South Pole aerosol 0.8-2‰ Site A, Greenland ice core 0.5-3‰ Vostok & Dome C ice cores 1.3-4.8‰ Desert dust traps 0.3-3.5‰ INDOEX aerosol 0.5-3‰ Alert 1.0‰

23. Alkalinity in the Marine Boundary Layer Na +, Cl -, HCO 3 - /CO 3 2- pH=8 Acids: H 2 SO 4 (g) HNO 3 (g) RCOOH(g) SO 2 (g)  SO 4 2- O3O3 CO 2 (g) H + + HCO 3 -  H 2 OCO 2

24. DMS SO 2 Free troposphere H 2 SO 4 (g) OH Cloud other aerosols (acid or neutral) O3O3 CO 2 (g) H2O2H2O2 Emission Marine Boundary Layer Subsidence OH NO 3 Sea-salt aerosol HCO 3 - /CO 3 2- Emission RCOOH(g) HNO 3 (g) Subsidence Deposition NH 3 (g) GEOS-CHEM Sea-salt Alkalinity http://www-as.harvard.edu/chemistry/trop/geos/index.html SO 4 2-

25. March 1998 January 1997 Na + [  g m -3 ] 31 11975 0 13 INDOEX Cruises High volume air sampler GEOS-CHEM Sea-Salt Pre-INDOEX Jan. 1997INDOEX March 1998

26. Pre-INDOEX Cruise January 1997 Alexander et al., 2005

27. INDOEX Cruise March 1998 Alexander et al., 2005

28. GEOS-CHEM Alkalinity Budget f SO2 f HNO3 f excess 0.10.30.50.7

29. [SO 2 ] % decrease [SO 4 2- ] % increase SO 2 + OH % decrease 10305070 5 GEOS-CHEM Sulfur Budget Marine DMS and Climate Charleson et al., 1987; Shaw 1985

30. 0.0 1.63.24.7 6.3 ‰ JanuaryJuly GEOS-CHEM: Seasonal Variability in  17 O Sulfate South Pole aerosol 0.8-2‰ Alert aerosol 1‰

31. Arctic Haze Formation Sulfate ng m -3 Picture from L. Barrie Sirois et al., 1999

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

33. Arctic Night-time Chemistry S IV + ½ O 2  S VI Mn 2+, Fe 3+  17 O = 0‰ ?? From Sirois and Barrie, 1999 xV (ng m -3 )

34. GEOS-CHEM Measurements GEOS-CHEM [Fe(III)] = 0.5  mol/l [Mn(II)] = 0.05  m/l Measurements Alert: Metal Catalysis? GEOS-CHEM [Fe(III)] = 0.5  mol/l [Mn(II)] = 0.05  m/l [Fe(III)] = 5.0  mol/l [Mn(II)] = 0.5  m/l Measurements

35. Metals: Greenland ice core record Hong et al., 1996 Candelone et al., 1995 GRIP Summit 1773 1992

36. Conclusions “Minor” oxidants significant in polar regions during winter. Important for interpreting ice core records. Alkaline sea-salt aerosols impact sulfate formation and hence radiative properties of sulfate aerosols.

37. Some Future Directions Fe, Si, … CaCO 3 CO 2 (g) Acids: H 2 SO 4 (g) HNO 3 (g) RCOOH(g) SO 2 (g)  SO 4 2- Dust (Fe) From Meskhidze et al., 2005 Oceanic Phytoplankton

38. Some Future Directions NASA GISS general circulation model (GCM) GEOS-CHEM chemical transport model (CTM) Wetland CH 4 emissions (BIOME4) Present day LGM David Rind (Columbia/NASA) Loretta Mickley Shiliang Wu Jed Kaplan

39. Acknowledgements Mark H. Thiemens Charles C.W. Lee Justin McCabe Joël Savarino Robert Delmas Daniel Jacob Rokjin Park Loretta Mickley Bob Yantosca Daly Postdoctoral Fellowship (EPS)