Investigating the influence of the Investigating the influence of the marine biosphere on climate: marine biosphere on climate:

Oxygen isotope measurements and Oxygen isotope measurements and model simulationsmodel simulations

Becky Alexander

Harvard University

Department of Earth and Planetary Sciences

USC May 4, 2004

• Sulfate aerosols: Importance and uncertainties 17O 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

OverviewOverview

Importance of Atmospheric SulfateImportance of Atmospheric Sulfate

Cooling effect on climate

Contributes to the formation of acid rain

Anthropogenic emissions are 2 to 3 times that of natural sources

Transcontinental transportPark et al., 2004

Surface

DMSCS2

H2SSO2 SO4

2- OH

O3, H2O2

OH, NO3

MSA

OH

Atmospheric Sulfur BudgetAtmospheric Sulfur Budget

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

IPCC report, 2001

Effects of Aerosols on ClimateEffects of Aerosols on ClimateDirect Effect

Reflection

RefractionAbsorption

Indirect Effect

Ramanathan et al., 2001

Aerosol number density (cm-3)

Clo

ud

dro

ple

t n

um

be

r d

en

sity

(cm

-3)

Atmospheric Aerosol Formation Atmospheric Aerosol Formation and Photosynthetic Rateand Photosynthetic Rate

Mt. Pinatubo volcano

Gu et al., 2003

h

Biology and Aerosol Climate EffectsBiology and Aerosol Climate Effects

SO2 H2SO4

OH New particle formation

CCN

Light scattering

DMS

OH NO3

Phytoplankton

O 3, H 2

O 2

SO42-

Biological regulation of the climate?

Mass-Dependent FractionationMass-Dependent Fractionation(‰) = [(Rsample/Rstandard) – 1] 1000

18O: R = 18O/16O; 17O: R = 17O/16O

17O/18O 0.5

Mass-Independent FractionationMass-Independent Fractionation

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

*

Explanation of Mass-independent EffectExplanation of Mass-independent Effect

Non-RRKM (Rice-Rampsberger-Kassell-Marcus) transition state

theory:

(asymm) /(symm) = 1.18

Gao and Marcus, 2001

Alt

i tu

de

(km

)

17OSMOW (‰)

0 10 20 30 40 50 60

10

20

30

40

50

60

Measured O3

HO2

OH

O3

Rainwater H2O2

HO2+HO2H2O2+O2

Tropopause

1717O of oxidantsO of oxidantsPhotochemical Box Model

Lyons, GRL, 2001

Tropospheric 17O values

O3: 35‰

H2O2: 1.7‰

OH: 0‰

Source ofSource of 1717OO SulfateSulfate

SO2 in isotopic equilibrium with H2O :

17O of SO2 = 0 ‰

1) SO32- + O3 (17O=35‰) SO4

2- 17O = 8.75 ‰

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 = 0.85 ‰ Aqueous

Gas

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, pH=4.5) 17O=0.85‰

S(IV) + O3 (in cloud, pH=4.5) 17O=8.75‰

Use constant, global 17O value for oxidants

17O ‰ method reference

O3 35 Photochemical model

Lyons 2001

H2O2 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‰

Missing O3 oxidation source

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

OO33 oxidation on sea-salt aerosols oxidation on sea-salt aerosols

Sea-salt emissions are a function of wind speed

pH = 8, O3 oxidation dominant1

4

iit D

rAk i

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

GEOS-CHEM sea-salt emissionsGEOS-CHEM sea-salt emissions

0.0 Tg 0.59 Tg 1.17 Tg

January 1997 July 1997

INDOEX

Pre-INDOEX Jan. 1997 INDOEX March 1998

INDOEX cruises – INDOEX cruises – 1717O sulfateO sulfate

Analytical MethodAnalytical Method

High volume air sampler

H2SO4

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 CruisePre-INDOEX CruiseJanuary 1997

0

0.5

1

1.5

2

2.5

3

3.5

-15.0 -10.0 -5.0 0.0 5.0 10.0 15.0

Latitude (degrees)

SO

42-

nss

17

O (

‰)

0

0.5

1

1.5

2

2.5

3

3.5

-15.0 -10.0 -5.0 0.0 5.0 10.0 15.0

Latitude (degrees)

SO

42-

nss

17

O (

‰)

0

0.5

1

1.5

2

2.5

3

3.5

-15.0 -10.0 -5.0 0.0 5.0 10.0 15.0

Latitude (degrees)

SO

42-

nss

17

O (

‰)

ITCZ

Enhanced pH of sea-salt aerosols Enhanced pH of sea-salt aerosols over sea water?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-)

0

1

2

3

4

5

6

7

8

9

-15.0 -10.0 -5.0 0.0 5.0 10.0 15.0

Latitude (degrees)

SO

42-

nss

17

O (

‰)

Pre-INDOEX CruisePre-INDOEX CruiseJanuary 1997

0.00

0.50

1.00

1.50

2.00

2.50

-15 -10 -5 0 5 10 15Latitude (degrees)

SO

42

- ns

s 1

7 O (

‰)

0.00

0.50

1.00

1.50

2.00

2.50

-15 -10 -5 0 5 10 15Latitude (degrees)

SO

42

- ns

s 1

7 O (

‰)

0.00

0.50

1.00

1.50

2.00

2.50

-15 -10 -5 0 5 10 15Latitude (degrees)

SO

42

- ns

s 1

7 O (

‰)

INDOEX Cruise INDOEX Cruise

March 1998

ITCZ

0% 50% 100%

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)

|100|

CaseA

CaseBCaseA

Chemical effect of sea-salt on SOChemical effect of sea-salt on SO22 and and

SOSO442-2- concentrations concentrations

50%0% 100%

Effect of sea-salt chemistry on gas-phase Effect of sea-salt chemistry on gas-phase sulfate production ratessulfate production rates

|100|

CaseA

CaseBCaseA

Mar/Apr/May Jun/Jul/Aug

Sep/Oct/Nov Dec/Jan/Feb

Percent (%) decrease (seasonal average):

Sulfate Formation in the Marine Sulfate Formation in the Marine Boundary LayerBoundary Layer

DMS OHNO3 SO2 H2SO4OH

New particle formation

CCN

H2O2

Light scattering

Gas-phaseAqueous-phase

Aqueous-phase

O3

Phytoplankton

Lessons from INDOEX and GEOS-CHEMLessons from INDOEX and GEOS-CHEM•The evolution of alkalinity depends on atmospheric acidity and has a

short (< 1hour) atmospheric lifetime.

•The acidification of the atmosphere, particularly in the

Northern Hemisphere, may have increased the effectiveness of the

marine biological control on climate.

•Sulfate formation on sea-salt chemistry should be included in models estimating the radiative

effects of sulfate from DMS emissions.

Ship SO2 in North Atlantic

0 3.3 6.6 106 kg S

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

La Jolla rainwater 1.1 ‰ pH=5.1

Davis, CA fogwater 4.3 ‰ pH=6.2

INDOEX aerosol 0.5-3‰

La Jolla aerosol 0.2-1.4‰

White Mtn, CA aerosol 1-1.7‰

South Pole aerosol 0.8-2‰

Vostok & Dome C ice cores 1.3-4.8‰

Whiteface Mtn, NY fogwater 0.3 ‰ pH=2.9

Site A, Greenland ice core 2‰January 1997 July 1997

Desert dust traps 0.3-3.5‰

Future Plans – DustFuture Plans – Dust

Mwskhidze et al., 2003

SOSO22 Oxidation, Iron Mobilization, Oxidation, Iron Mobilization,

and Oceanic Productivityand Oceanic Productivity

Future Plans – Organic AerosolsFuture Plans – Organic Aerosols

Current understanding is very limited!

13C is the only isotope system measured.

-pinene -pinene

OH, O3

NO3

Formic acid Acetic acid…

~100 ppt in remote MBL!

AcknowledgementsAcknowledgements

NOAA Climate and Global Change Postdoctoral Fellowship

Daly Postdoctoral Fellowship (Department of Earth and Planetary Sciences, Harvard University)

Daniel Jacob

Dan Schrag

Ann Pearson

Rokjin Park

Qinbin Li

Bob Yantosca

Mark H. Thiemens

Charles Lee

Joël Savarino

V. Ramanathan

Atmospheric Aerosol Formation Atmospheric Aerosol Formation and Photosynthetic Rateand Photosynthetic Rate

Gu et al., 2003

Mt. Pinatubo volcano Aerosol Optical Depth

Explanation of Mass-Independent EffectExplanation of Mass-Independent Effect

(asymm) /(symm) = 1.18

O + O2 O3* + M O3

Assymetric: 18O16O16O* Symmetric: 16O18O16O*

Gao and Marcus, 2001

Non-RRKM (Rice-Rampsberger-Kassell-

Marcus) transition state theory:

XY+X X+YX

XY+Z X+YZ

XYX

XYZ