Marine biogenic emissions, sulfate aerosol formation, and climate:

Constraints from oxygen isotopes

Becky Alexander

Harvard University

University of Wisconsin, Madison

February 21, 2005

OverviewOverview

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

16

16 17 or 18

Radiative Forcing: Greenhouse Radiative Forcing: Greenhouse Gases and AerosolsGases and Aerosols

IPCC report, 2001

Effects of Aerosols on ClimateEffects of Aerosols on ClimateDirect Effect

Indirect Effect

Reflection

RefractionAbsorption

Ramanathan et al., 2001

Aerosol number density (cm-3)

Clo

ud

dro

ple

t n

um

be

r d

en

sity

(cm

-3)

Atmospheric SulfateAtmospheric 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 transportPark et al., 2004

Sulfur Cycle in the AtmosphereSulfur Cycle in the Atmosphere

Surface

DMSCS2

H2SSO2 SO4

2- OH

O3, H2O2

OH, NO3

MSA

OH

New Particle FormationNew Particle Formation

SO2 + OH (+O2 + H2O) H2SO4(g) (+HO2)

CCN> ~ 0.1 m

H2O

NH3?

H2SO4(g)

Condensation

RCOOH

Activation

Water vaporWater vapor

Updraft velocityUpdraft velocity

Aerosol number densityAerosol number density

Size distributionSize distribution

Chemical compositionChemical composition

From Boucher and Lohmann, 1995

nssSO42- (mg m-3)

CD

NC

(m

-3)

Marine Biologic DMS and ClimateMarine Biologic DMS and ClimateCharleson Charleson et alet al. (1987), Shaw (1985). (1987), Shaw (1985)

SO2 H2SO4OH New particle

formation

CCN

Light scattering

DMSOH NO3

Phytoplankton

H 2O 2

SO42-

O3

Sea-salt aerosol

Stable Isotope Measurements: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-….)

17O/18O 0.5

Mass-Independent Fractionation (MIF)Mass-Independent Fractionation (MIF)

17O/18O 1

-80

-60

-40

-20

0

20

40

60

-100 -80 -60 -40 -20 0 20 40 60 8018O

17O

Product Ozone

Residual Oxygen

Starting Oxygen

Thiemens and Heidenreich, 1983

17O

17O

17O = 17O – 0.5*18O 0

O + O2 O3*

Mass-dependent fractionation line: 17O/18O 0.5

Symmetry C2v Symmetry Cs

17 or 18

16 16

16

16 17 or 18E Vibrational

StatesRotational

States

De

v = i

v=i+1

RotationalStates

VibrationalStates

De

v = i

v=i+1

O2 + O(3P) O3

*

Symmetry Based Explanation of MIFSymmetry Based Explanation of MIF

25

10

5

50

75

100

10 20 50 100

SO4

CO

N2O

H2O2

NO3

CO2 strat.

O3

trop.

O3

strat.

18O

17O

1717OO Measurements in the AtmosphereMeasurements in the Atmosphere

Source ofSource of 1717OO SulfateSulfateSO2 in isotopic equilibrium with H2O :

17O of SO2 = 0 ‰

1) SO32- + O3 (17O=35‰) SO4

2- 17O = 8.8 ‰

17O of SO42- a function relative amounts of OH, H2O2, and O3 oxidation

Savarino et al., 2000

3) SO2 + OH (17O=0‰) SO42- 17O = 0 ‰

2) HSO3-+ H2O2 (17O=1.7‰) SO4

2- 17O = 0.9 ‰ Aqueous

Gas

S(IV) = SO2, HSO3-, SO3

2-

pH dependency of OpH dependency of O33 oxidation and oxidation and

its effect on its effect on 1717O of SOO of SO442-2-

1.0E-15

1.0E-14

1.0E-13

1.0E-12

1.0E-11

1.0E-10

1.0E-09

1.0E-08

1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

pH

Oxi

dat

ion

rat

e (M

/sec

)

H2O2

O3

1.0E-151.0E-141.0E-13

1.0E-121.0E-111.0E-101.0E-091.0E-08

1.0E-071.0E-061.0E-051.0E-041.0E-03

1.0E-021.0E-011.0E+00

1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

pH

Oxi

dat

ion

rat

e (M

/sec

)

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

17

O (

‰)

H2O2

O3

Lee et al., 2001 Sea-spray

17Omeas = ƒOH*0‰ + ƒH2O2*0.9‰ + ƒO3*8.8‰

ƒOH + ƒH2O2 + ƒO3 = 1

GEOS-CHEMGEOS-CHEM

• 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)

http://www-as.harvard.edu/chemistry/trop/geos/index.html

GEOS-CHEM GEOS-CHEM 1717O Sulfate SimulationO Sulfate Simulation

SO2 + OH (gas phase) 17O=0‰

S(IV) + H2O2 (in cloud) 17O=0.9‰

S(IV) + O3 (in cloud, sea-salt) 17O=8.8‰

Assume constant, global 17O value for oxidants

17O ‰ method reference

O3 35 Photochemical model

Lyons 2001

H2O2 1.3-2.2 (1.7)

Rainwater measurements

Savarino and Thiemens 1999

OH 0 Experimental Dubey et al., 1997

1717O sulfate: GEOS-CHEM and measurementsO sulfate: GEOS-CHEM and measurements

January 2001 July 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‰

Alkalinity in the Marine Boundary LayerAlkalinity in the Marine Boundary Layer

Na+, Cl-, CO3

2-

pH=8CO2(g)

Acids:

H2SO4(g)

HNO3(g)

RCOOH(g)

SO2(g) SO42-

Pre-INDOEX Jan. 1997 INDOEX March 1998

INDOEX cruisesINDOEX cruises

Analytical MethodAnalytical Method

High volume air samplerSO4

2-

Ion Chromatograph Ionic separation

O2 loop 5A mol.sieve

vent

Isotope Ratio Mass Spectrometer

Ag2SO4 O2 + SO2

Removable quartz tube

1050°C

magnet

To vacuum

To vacuumGC

SO2 trap

He flow

Sample loop 5A mol.sieve

ventSO2 port

O2 port

pre-INDOEX 1997 INDOEX 1998

9

0

1

2

3

4

5

6

7

8

-15 -10 -5 0 5 10 15 -15 -10 -5 0 5 10 15

Latitude (°N)

0

1

2

3

4

5

6

7

8

nss

SO

42

- 1

7 O (

‰)

Na

+ (g

/m3)

bulk

finecoarse

DMS

SO2

Free troposphere

H2SO4(g)

OH

Cloud other aerosols

(acid or neutral)

O3

CO2(g)

H 2O

2

Emission

Marine Boundary Layer

Subsidence

OH NO3

Sea-salt aerosol CO3

2-

Emission

HNO3(g)RCOOH(g)

Subsidence

Deposition

NH3(g)

GEOS-CHEM Sea-salt AlkalinityGEOS-CHEM Sea-salt Alkalinityhttp://www-as.harvard.edu/chemistry/trop/geos/index.html

SO42-

March 1998

January 1997

Na+ [g m-3]31 119750 13

Model Sea-salt (NaModel Sea-salt (Na++) Concentrations) ConcentrationsdF/dr = 1.373u10

3.41r-3(1+0.057r1.05)101.19exp(-B2)

= (0.380 log r)/0.65

Monahan et al., 1986 (particles m-2 s-1 m-1)

INDOEX 1998

nss

SO

42

- 1

7O

(‰

)

Latitude (°N)

Model not including sea-salt chemistry

Model including sea-salt chemistry

Observations

pre-INDOEX 1997

INDOEX 1998

GEOS-CHEM Alkalinity BudgetGEOS-CHEM Alkalinity Budget

fSO2

fHNO3

fexcess

0.1 0.3 0.5 0.7

[SO2] % decrease

[SO42-] % increase

SO2 + OH % decrease

10 30 50 705

GEOS-CHEM Sulfur BudgetGEOS-CHEM Sulfur Budget

Excess Alkalinity Sources?Excess Alkalinity Sources?

OH chemistryOH chemistry

Na+, Cl-

OH(g) + Cl-(interface) (HO…Cl-)interface

(HO…Cl-)interface + (HO…Cl-)interface Cl2 + 2OH-

2OH•

2OH-

Cl2

Laskin et al., 2003

Excess Alkalinity Sources?Excess Alkalinity Sources?

Biogenic CaCOBiogenic CaCO33

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)

nss

SO

42

- 1

7O

(‰

)

Model with excess alkalinity

Observations

Model with doubled alkalinity supply

Excess alkalinity

(OH chemistry)

Biogenic alkalinity

(CaCO3)

SeaWiFS Ocean ColorSeaWiFS Ocean Color(NASA)(NASA)

January 1998 March 1998

Dust AlkalinityDust Alkalinity

Fe, Si, …

CaCO3

CO2(g)

Acids:

H2SO4(g)

HNO3(g)

RCOOH(g)

SO2(g) SO42-

> 1: Fe mobilizationAlkalinity

Acid

Meskhidze et al., 2005

SOSO22 Oxidation, Iron Mobilization, Oxidation, Iron Mobilization,

and Oceanic Productivityand Oceanic Productivity

From Meskhidze et al., 2005

ConclusionsConclusions

•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 SO2

•Decreases in SO2 concentrations and the rate of gas-phase sulfate production (10 - 30%) in the MBL

•Inclusion of sea-salt chemistry in global models is important for interpretation of Antarctic ice core 17O sulfate

measurements

Vostok Ice Core Vostok Ice Core

1717O (SOO (SO442-2-) variability) variability

Ts data: Kuffey and Vimeux, 2001, Vimeux et al., 2002

Alexander et al., 2002

0

1

2

3

4

5

6

0 20 40 60 80 100 120 140

Age (kyr)

17O

-6

-5

-4

-3

-2

-1

0

1

2

3

Ts

17O

(‰

)

Ts

Climate Variations in the Oxidation Climate Variations in the Oxidation Pathways of Sulfate FormationPathways of Sulfate Formation

OH (gas-phase) oxidation greater in glacial period compared to interglacial

Age (kyr)

% O

H

0

10

20

30

40

50

60

70

80

90

0 20 40 60 80 100 120 140

Age (kyr)

-6

-5

-4

-3

-2

-1

0

1

2

3

T

s

Secondary Species

CO2, H2SO4, O3, …

Oxidizing Power of the AtmosphereOxidizing Power of the Atmosphere

VolcanoesMarine Biogenics

Biomass burning

Continental Biogenics

Primary Species H2S, SO2, CH4, CO, DMS, CO2, NO, N2O,

particulates

?

Climate change

OHhH2O

Primary Emissions

DMS, SO2, CH4, …

AcknowledgementsAcknowledgements

Mark H. Thiemens

Charles Lee

Joël Savarino

Daniel Jacob

Rokjin Park

Qinbin Li

Bob Yantosca

Duncan Fairlie