Marine biogenic emissions, sulfate aerosol formation, and climate: Constraints from oxygen isotopes Becky Alexander Harvard University University of Wisconsin, Madison February 21, 2005

Overview Introduction to aerosols, climate, and oxygen isotopes (Mass-independent fractionation) Chemistry and climate interactions on the glacial/interglacial timescale Influence of sea-salt aerosol alkalinity in sulfate aerosol formation  climate implications or 18

Radiative Forcing: Greenhouse Gases and Aerosols IPCC report, 2001

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 )

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

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

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 )

Marine Biologic DMS and Climate Charleson et al. (1987), Shaw (1985) SO 2 H 2 SO 4 OHNew particle formation CCN Light scattering DMS OHNO 3 Phytoplankton H2O2H2O2 SO 4 2- O3O3 Sea-salt aerosol

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

Mass-Independent Fractionation (MIF)  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

Symmetry C 2v Symmetry C s 17 or or 18 E Vibrational States Rotational States DeDe v = i v=i+1 Rotational States Vibrational States DeDe v = i v=i+1 O 2 + O( 3 P) O 3 * Symmetry Based Explanation of MIF

SO 4 CO N2ON2O H2O2H2O2 NO 3 CO 2 strat. O 3 trop. O 3 strat.  18 O  17 O  17 O Measurements in the Atmosphere

Source of  17 O Sulfate SO 2 in isotopic equilibrium with H 2 O :  17 O of SO 2 = 0 ‰ 1) SO 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., ) SO 2 + OH (  17 O=0‰)  SO 4 2-  17 O = 0 ‰ 2) HSO H 2 O 2 (  17 O=1.7‰)  SO 4 2-  17 O = 0.9 ‰ Aqueous GasS(IV) = SO 2, HSO 3 -, SO 3 2-

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  17 O meas = ƒ OH *0‰ + ƒ H2O2 *0.9‰ + ƒ O3 *8.8‰ ƒ OH + ƒ H2O2 + ƒ O3 = 1

GEOS-CHEM Global 3-D model of atmospheric chemistry 4ºx5º horizontal resolution, layers in vertical Driven by assimilated meteorology (1987 –present). Includes aqueous and gas phase chemistry: S(IV) + OH (gas-phase) S(IV) + O 3 /H 2 O 2 (in-cloud, pH=4.5) Off-line sulfur chemistry (uses monthly mean OH and O 3 fields from a full chemistry, coupled aerosol simulation)

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, sea-salt)  17 O=8.8‰ Assume constant, global  17 O value for oxidants  17 O ‰ methodreference O3O3 35 Photochemical model Lyons 2001 H2O2H2O (1.7) Rainwater measurements Savarino and Thiemens 1999 OH0 ExperimentalDubey et al., 1997

 17 O sulfate: GEOS-CHEM and measurements January 2001July ‰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 ‰ South Pole aerosol 0.8-2‰ Site A, Greenland ice core 0.5-3‰ Vostok & Dome C ice cores ‰ Desert dust traps ‰ INDOEX aerosol 0.5-3‰ Alert 1.0‰

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-

Pre-INDOEX Jan. 1997INDOEX March 1998 INDOEX cruises

Analytical Method High volume air sampler SO 4 2- 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

pre-INDOEX 1997 INDOEX Latitude (°N) nssSO 4 2-  17 O (‰) Na + (  g/m 3 ) bulk fine coarse

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 SO 4 2-

March 1998 January 1997 Na + [  g m -3 ] Model Sea-salt (Na + ) Concentrations dF/dr = 1.373u r -3 ( r 1.05 ) exp(-B 2 )  = (0.380 log r)/0.65 Monahan et al., 1986 (particles m -2 s -1  m -1 )

INDOEX 1998 nssSO 4 2-  17 O (‰) Latitude (°N) Model not including sea-salt chemistry Model including sea-salt chemistry Observations pre-INDOEX 1997 INDOEX 1998

GEOS-CHEM Alkalinity Budget f SO2 f HNO3 f excess

[SO 2 ] % decrease [SO 4 2- ] % increase SO 2 + OH % decrease GEOS-CHEM Sulfur Budget

Excess Alkalinity Sources? OH chemistry Na +, Cl - OH (g) + Cl - (interface)  (HO…Cl - ) interface (HO…Cl - ) interface + (HO…Cl - ) interface  Cl 2 + 2OH - 2OH 2OH - Cl 2 Laskin et al., 2003

Excess Alkalinity Sources? Biogenic CaCO 3 Coccolithophore phytoplankton cell Image credit: Dr Jeremy R. Young, the Natural History Museum of London Coccolithophore bloom in the Bering Sea Image credit: NASA

Latitude (°N) nssSO 4 2-  17 O (‰) Model with excess alkalinity Observations Model with doubled alkalinity supply Excess alkalinity (OH chemistry) Biogenic alkalinity (CaCO 3 )

SeaWiFS Ocean Color (NASA) January 1998March 1998

Dust Alkalinity Fe, Si, … CaCO 3 CO 2 (g) Acids: H 2 SO 4 (g) HNO 3 (g) RCOOH(g) SO 2 (g)  SO 4 2- > 1: Fe mobilization Meskhidze et al., 2005

SO 2 Oxidation, Iron Mobilization, and Oceanic Productivity From Meskhidze et al., 2005

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 Decreases in SO 2 concentrations and the rate of gas- phase sulfate production ( %) in the MBL Inclusion of sea-salt chemistry in global models is important for interpretation of Antarctic ice core  17 O sulfate measurements

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

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

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, …

Acknowledgements Mark H. Thiemens Charles Lee Joël Savarino Daniel Jacob Rokjin Park Qinbin Li Bob Yantosca Duncan Fairlie