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Paleo-oxidant variations and atmospheric aerosol formation: The ice-core record

Paleo-oxidant variations and atmospheric aerosol formation: The ice-core record. Becky Alexander Harvard University Department of Earth and Planetary Sciences. USC May 3, 2004. Outline.

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Paleo-oxidant variations and atmospheric aerosol formation: The ice-core record

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  1. Paleo-oxidant variations and atmospheric aerosol formation: The ice-core record Becky Alexander Harvard University Department of Earth and Planetary Sciences USC May 3, 2004

  2. Outline Antarctic ice core record: Atmospheric composition and climate variations on the glacial/interglacial timescale  What controls the composition of the atmosphere? (importance of ocean, biosphere, and oxidizing power of the atmosphere)  How does this impact climate change? (greenhouse gases and aerosols)  What have we learned from the O-isotope record of sulfate? Greenland ice core record: Atmospheric composition variations in the Industrial Era  How have humans impacted atmospheric chemistry?  When did the anthropogenic era begin?

  3. CO2 (ppbv) dD (‰) CH4 (ppbv) 0 50 100 150 200 250 300 350 400 Age (kyr BP) From Kotlyakov et al., 2001 The Vostok Ice Core Record: Greenhouse gases

  4. Milankovitch Cycles Eccentricity Periodicity ~100,000 years Tilt Periodicity ~41,000 years What drives changes in CO2 and CH4 concentrations from glacial to interglacial periods? Precession Periodicity ~22,000 years

  5. Glacial/Interglacial CO2 variations Dust deposition and Chlorophyll Biological productivity: nutrients + DIC  POM Euphotic zone POM -0.8 0.0 0.8 Correlation coefficient from Erickson et al., 2000 Jouzel et al., 1993 “Iron hypothesis” Martin, 1990 adapted from Ridgwell, 2002

  6. Glacial/Interglacial CH4 variations Wetland CH4 emissions Present day Wetland CH4 emissions 24% less in LGM. Not enough to explain glacial/interglacial change in atmospheric CH4 concentrations. Changes in atmospheric chemistry leading to CH4 destruction? LGM Kaplan, 2002

  7. Oxidizing Power of the Atmosphere Climate change ? OH hn, H2O Primary Emissions DMS, SO2, CH4, … Secondary Species CO2, H2SO4, O3, … To what extent is the oxidizing power of the atmosphere controlled by the biosphere? Model simulations by Thompson et al. (1993), using the Vostok CH4 constraint, calculate 32% greater OH concentrations during the LGM. 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

  8. The Vostok Ice Core Record: Aerosols dD (‰) SO42- (ppb) dD from Jouzel et al., 1987 [SO42-] from M. Legrand [SO42-] tracks [MSA-] suggesting a predominant DMS (oceanic biogenic) source

  9. Aerosol Climate Effects SO42- O3, H2O2 CCN SO2 OH New particle formation H2SO4 Does the marine biosphere regulate the climate through the production of DMS? OH NO3 Light scattering DMS Phytoplankton

  10. NOx NOx HNO3 HNO3 O3, NO hu, O(1D) O2, H2O HO2 H2SO4 H2SO4 H2SO4 SOx SOx SOx Oxidants in the Sulfur Cycle CH4 CO HC NOx O3 H2O2 OH

  11. Key Questions How has the oxidation capacity of the atmosphere varied in the past (glacial/interglacial cycles)? How have anthropogenic emissions affected the oxidation capacity of the atmosphere? What can we expect in the future?

  12. 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

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

  14. Conservative Tracers in Ice cores Na+ SO42- Composition of gas bubbles SO42- very stable (D17O) oxidant concentrations  oxidation capacity of the atmosphere?

  15. 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

  16. 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

  17. All D17O measurements in the atmosphere O3 strat. 100 O3 trop. 75 CO2 strat. 50 NO3 25 N2O 10 H2O2 CO 5 SO4 10 20 50 100 d17O (‰) d18O (‰)

  18. 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

  19. Analytical Procedure Decontamination Concentrate Ion Chromatograph Ionic separation H2SO4 Ag2SO4

  20. Analytical Procedure 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 Isotope Ratio Mass Spectrometer Faster, smaller sample sizes, O and S isotopes in same sample

  21. Vostok Ice Core Climatic D17O (SO42-) fluctuations D17O (‰) DTs DTs data: Kuffey and Vimeux, 2001, Vimeux et al., 2002 Alexander et al., 2002

  22. Vostok 3-isotope plot slope1

  23. Vostok sulfate three-isotope plot Vostok trendline Tropospheric O3 Vostok trendline Vostok trendline Vostok trendline Vostok trendline Tropospheric O3 Tropospheric O3 Tropospheric O3 100% O3 H2O2 H2O2 Mass-Dependent line 100% OH Mass-Dependent line Mass-Dependent line Mass-Dependent line Mass-Dependent line H2O/OH 100% O3 oxidation: D17O (SO4) = ¼ * 35‰ = 8.75‰ 100% OH oxidation: D17O (SO4) = 0 ‰ H2O/OH 100% H2O2 oxidation: D17O(SO4) = ½*1.7‰ = 0.85 ‰ D17O range = 1.3 – 4.8 ‰

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

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

  26. Lessons from Vostok OH D17O of sulfate varies with climate, reflects variations in oxidant concentrations and/or cloud processing efficiency Increased (30-80% range) gas-phase formed sulfate during the glacial period  positive climate feedback?

  27. Site A, Greenland Ice Core GISP2 Site A nssSO42- (ppb) GISP2 Site A Alexander et al., 2004 Mayewski et al., 1997

  28. Atmospheric nitrate formation D17O of HNO3 a function of HO2/O3 and the terminal reaction The D17O of HNO3 depends also on the dilution factor due to the terminal reaction NO2 + OH  HNO3 NO2 + O3 NO3 + RH  HNO3 NO3 + NO2 N2O5 + H2O(aq) 2HNO3 D17O of NOx is a function of HO2/O3 oxidation NO NO2 + HO2/O3 NO2/NO3 + HO/O2

  29. Site A, Greenland D17O (‰) D17O (‰) nssSO42- D17O (‰) NO3-

  30. Preindustrial Biomass Burning Alexander et al., 2004 Savarino and Legrand, 1997

  31. SIV + O3 SVI SIV + H2O2 SVI SIV + O3 SVI SIV + H2O2 SVI N2O5 + H2O 2HNO3 Biomass burning emissions NO2 + OH HNO3 SO2 + OH + H2O H2SO4 NMHC O3 (aq) NO2 + O3 NO3 + O2 NO3 + HC HNO3 NO3 + NO2 N2O5 N2O5 + H2O(aq) 2HNO3 NOx SO2 NMHC O3 NO+H/RO2 NO2 + H/RO NO+O3 NO2 + O2 DMS NMHC NMHC NMHC NMHC Wet/Dry Deposition Ash, … Wet/Dry Deposition North America Greenland Ocean

  32. Conclusions Large biomass burning signal in D17O of sulfate and nitrate  anthropogenic effects on atmospheric chemistry began prior to the Industrial Revolution D17O of sulfate varies with climate, reflects variations in oxidant concentrations and/or cloud processing efficiency Increased (30-80% range) gas-phase formed sulfate during the glacial period  positive climate feedback?

  33. Future Directions This is just the beginning! Higher resolution data over various timescales  WAISCORES Aerosol and snow pit samples from the Canadian Arctic  interactions between the Arctic climate, sea ice, marine productivity, and the formation of Arctic haze Global model simulations using oxygen isotope tracers: interpret and quantify existing data sets direct future measurement sites

  34. Acknowledgements Mark H. Thiemens Charles Lee Greg Michalski Peter Zmolek Phoebe Glazer Joël Savarino Robert Delmas J.R. Petit Karl Kreutz Jeff Severinghaus Allison Shaw Mark Twickler Geoffrey Hargreaves James Farquhar

  35. Glacial/Interglacial CO2 variations From Gildor and Tziperman, 2001 “Sea-ice switch”

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