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Becky Alexander Harvard University Department of Earth and Planetary Sciences

Investigating the influence of the marine biosphere on climate: Oxygen isotope measurements and model simulations. Becky Alexander Harvard University Department of Earth and Planetary Sciences. USC May 4, 2004. Overview. Sulfate aerosols: Importance and uncertainties

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Becky Alexander Harvard University Department of Earth and Planetary Sciences

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  1. Investigating the influence of the marine biosphere on climate: Oxygen isotope measurements and model simulations Becky Alexander Harvard University Department of Earth and Planetary Sciences USC May 4, 2004

  2. Overview • Sulfate aerosols: Importance and uncertainties • D17O sulfate: Resolve uncertainties • GEOS-CHEM: Global 3D model • INDOEX: INDian Ocean EXperiment • Sulfate formation in the marine boundary layer (MBL): Seasalt, biogenic DMS, Climate • Future Plans

  3. Contributes to the formation of acid rain Anthropogenic emissions are 2 to 3 times that of natural sources Importance of Atmospheric Sulfate Transcontinental transport Park et al., 2004 Cooling effect on climate

  4. CS2 DMS H2S Atmospheric Sulfur Budget OH, NO3 OH SO2 SO42- O3, H2O2 OH MSA Surface

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

  6. Effects of Aerosols on Climate Cloud droplet number density (cm-3) Indirect Effect l0 Reflection Aerosol number density (cm-3) l0 l0 Ramanathan et al., 2001 Absorption Refraction Direct Effect

  7. Atmospheric Aerosol Formation and Photosynthetic Rate Mt. Pinatubo volcano hn Gu et al., 2003

  8. OH NO3 DMS Phytoplankton Biology and Aerosol Climate Effects SO42- O3, H2O2 CCN OH SO2 New particle formation H2SO4 Light scattering Biological regulation of the climate?

  9. Mass-Dependent Fractionation (‰) = [(Rsample/Rstandard) – 1]  1000 18O: R = 18O/16O; 17O: R = 17O/16O d17O/d18O 0.5

  10. 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

  11. 16 O2 + O(3P) O3* 16 17 or 18 E Rotational States Vibrational States Vibrational States Rotational States v=i+1 v=i+1 v = i v = i De De Explanation of Mass-independent Effect Symmetry C2v Symmetry Cs 17 or 18 16 16 Non-RRKM (Rice-Rampsberger-Kassell-Marcus) transition state theory: r(asymm) /r(symm) = 1.18 Gao and Marcus, 2001

  12. 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 (‰)

  13. 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

  14. GEOS-CHEM http://www-as.harvard.edu/chemistry/trop/geos/index.html • Global 3-D model of atmospheric chemistry • 4ºx5º horizontal resolution, 26-30 layers in vertical • Driven by assimilated meteorology (1987 –present). • 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)

  15. GEOS-CHEM D17O Sulfate Simulation Use constant, global D17O value for oxidants SO2 + OH (gas phase) D17O=0‰ S(IV) + H2O2 (in cloud, pH=4.5) D17O=0.85‰ S(IV) + O3 (in cloud, pH=4.5) D17O=8.75‰

  16. 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

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

  18. O3 oxidation on sea-salt aerosols Sea-salt emissions are a function of wind speed pH = 8, O3 oxidation dominant Sea salt flux to atmosphere (Gong et al., 2002): 1.01 x 104 Tg/year  11.1 Tg(S)/year Global DMS emissions (Seinfeld and Pandis, 1998): 15-25 Tg(S)/year 44 -74% of SO2 (from DMS) oxidized to sulfate by O3 on sea-salt aerosols

  19. 0.0 Tg 0.59 Tg 1.17 Tg INDOEX GEOS-CHEM sea-salt emissions July 1997 January 1997

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

  21. Ag2SO4  O2 + SO2 He flow Removable quartz tube magnet To vacuum 1050°C SO2 trap SO2 port vent Sample loop 5A mol.sieve O2 port To vacuum GC Analytical Method High volume air sampler Ion Chromatograph Ionic separation H2SO4 Isotope Ratio Mass Spectrometer vent O2 loop 5A mol.sieve

  22. Pre-INDOEX Cruise January 1997 ITCZ

  23. Enhanced pH of sea-salt aerosols over sea water? Laskin et al. Science (2003): OH(g) + Cl-(interface) (HO…Cl-)interface (HO…Cl-)interface +(HO…Cl-)interface  Cl2 + 2OH- k(OH-)  k(SO42-)

  24. Pre-INDOEX Cruise January 1997

  25. INDOEX Cruise March 1998 ITCZ

  26. 0% 50% 100% Chemical effect of sea-salt on SO2 and SO42- concentrations Percent (%) change in concentrations (yearly average) Case A: SO2/SO42- concentration without sea-salt chemistry Case B: With sea-salt chemistry SO2 (decrease) SO42- (small increase)

  27. 0% 100% 50% Effect of sea-salt chemistry on gas-phase sulfate production rates Percent (%) decrease (seasonal average): Mar/Apr/May Jun/Jul/Aug Dec/Jan/Feb Sep/Oct/Nov

  28. Aqueous-phase O3 Sulfate Formation in the Marine Boundary Layer H2O2 Aqueous-phase CCN Gas-phase DMS OH New particle formation SO2 H2SO4 NO3 OH Light scattering Phytoplankton

  29. Lessons from INDOEX and GEOS-CHEM • The evolution of alkalinity depends on atmospheric acidity and has a short (< 1hour) atmospheric lifetime. • Sulfate formation on sea-salt chemistry should be included in models estimating the radiative effects of sulfate from DMS emissions. • The acidification of the atmosphere, particularly in the Northern Hemisphere, may have increased the effectiveness of the marine biological control on climate. Ship SO2 in North Atlantic 106 kg S 6.6 3.3 0

  30. D17O sulfate: GEOS-CHEM and measurements Desert dust traps 0.3-3.5‰ Davis, CA fogwater 4.3 ‰ pH=6.2 Whiteface Mtn, NY fogwater 0.3 ‰ pH=2.9 Site A, Greenland ice core 2‰ January 1997 July 1997 Vostok & Dome C ice cores 1.3-4.8‰ La Jolla rainwater 1.1 ‰ pH=5.1 La Jolla aerosol 0.2-1.4‰ White Mtn, CA aerosol 1-1.7‰ South Pole aerosol 0.8-2‰ INDOEX aerosol 0.5-3‰

  31. Future Plans – Dust

  32. SO2 Oxidation, Iron Mobilization, and Oceanic Productivity Mwskhidze et al., 2003

  33. Future Plans – Organic Aerosols Current understanding is very limited! d13C is the only isotope system measured. OH, O3 NO3 Formic acid Acetic acid… a-pinene b-pinene ~100 ppt in remote MBL!

  34. Acknowledgements Mark H. Thiemens Charles Lee Daniel Jacob Dan Schrag Ann Pearson Rokjin Park Qinbin Li Bob Yantosca V. Ramanathan Joël Savarino NOAA Climate and Global Change Postdoctoral Fellowship Daly Postdoctoral Fellowship (Department of Earth and Planetary Sciences, Harvard University)

  35. Atmospheric Aerosol Formation and Photosynthetic Rate Mt. Pinatubo volcano Aerosol Optical Depth Gu et al., 2003

  36. Explanation of Mass-Independent Effect O + O2 O3* + M  O3 Assymetric: 18O16O16O* Symmetric: 16O18O16O* XYX Non-RRKM (Rice-Rampsberger-Kassell-Marcus) transition state theory: X+YX XY+X XYZ r(asymm) /r(symm) = 1.18 X+YZ XY+Z Gao and Marcus, 2001

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