1. Marine biogenic emissions, sulfate formation, and climate: Constraints from oxygen isotopes Becky Alexander Harvard University Department of Earth and Planetary Sciences 6 th summer institute July 21, 2004

2. Marine biogenic emissions, sulfate formation and climate  17 O sulfate: Aerosol oxidation pathways INDOEX: INDian Ocean Experiment GEOS-CHEM: Global 3D model Overview

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

4. 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 )

5. Marine Biologic DMS and Climate Charleson et al. (1987) SO 2 H 2 SO 4 OHNew particle formation CCN Light scattering DMS OHOH NO 3 Phytoplankton H2O2H2O2 SO 4 2- O3O3 Sea-salt aerosol

6. Alkalinity in the Marine Boundary Layer Na +, Cl -, CO 3 2- pH=8 CO 2 (g) Acids: H 2 SO 4 (g) HNO 3 (g) RCOOH(g) SO 2 (g)  SO 4 2- OH ?

7. Stable Isotope Measurements: Tracers of source strengths and/or chemical processing of atmospheric constituents  (‰) = [(R sample /R standard ) – 1]  1000 R = minor X/ major X  18 O: R = 18 O/ 16 O  17 O: R = 17 O/ 16 O Standard = SMOW (Standard Mean Ocean Water) (CO 2, CO, H 2 O, O 2, O 3, SO 4 2- ….)  17 O /  18 O  0.5  17 O =  17 O – 0.5*  18 O = 0

8. Mass-Independent Fractionation  17 O /  18 O  1 Thiemens and Heidenreich, 1983  17 O  17 O  17 O =  17 O – 0.5 *  18 O  0 O + O 2  O 3 * Mass-dependent fractionation line:  17 O/  18 O  0.5

9. 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 = 8.75 ‰  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 = 0.85 ‰ Aqueous Gas

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

11. Pre-INDOEX Jan. 1997INDOEX March 1998 INDOEX cruises

12. Analytical Method High volume air sampler H 2 SO 4 Ion ChromatographIonic separation O 2 loop 5A mol.sieve vent Isotope Ratio Mass Spectrometer 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

13. 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 CO 3 2- Emission HNO 3 (g) RCOOH(g) Subsidence Deposition NH 3 (g) GEOS-CHEM Sea-salt Alkalinity http://www-as.harvard.edu/chemistry/trop/geos/index.html SO 4 2- OH

14. Pre-INDOEX Cruise January 1997 ITCZ

15. INDOEX Cruise March 1998 ITCZ

16. GEOS-CHEM Alkalinity Budget 60°N 60°S 180°W180°E ƒ SO 2 ƒ excess

17. Effect of sea-salt chemistry on SO 2 and sulfate concentrations |100|   Case1 Case2Case1 Percent (%) change (yearly average): SO 2 SO 4 2- 180°W 180°E 60°N 60°S 60°N 60°S

18. 50% 0%100% Effect of sea-salt chemistry on gas-phase sulfate production rates Mar/Apr/MayJun/Jul/Aug Sep/Oct/NovDec/Jan/Feb

19. Conclusions  Sulfate formation in sea-salt aerosols is limited by: Low to mid-latitudes: sea-salt flux to the atmosphere (wind) Mid to high-latitudes: gas-to-particle transfer rate of SO 2  SO 2 plays dominant role in titrating sea-salt alkalinity   17 O constraint indicates no significant regeneration of alkalinity through NaCl + OH reaction  Large decreases in SO 2 concentrations (70%) and the rate of gas-phase sulfate production (60%) in the MBL  Inclusion of sea-salt chemistry in global models is important for interpretation of Antarctic ice core  17 O sulfate measurements

20. Acknowledgements Mark H. Thiemens Charles Lee V. Ramanathan Joël Savarino Daniel Jacob Rokjin Park Qinbin Li Bob Yantosca

21. Mwskhidze et al., 2003 Source: www.nasa.gov SO 2 Oxidation, Iron Mobilization, and Oceanic Productivity