modeling and measurements of oxygen isotope tracers of sulfate formation: implications for the...
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Modeling and measurements of Modeling and measurements of oxygen isotope tracers of sulfate oxygen isotope tracers of sulfate
formation: Implications for the sulfur formation: Implications for the sulfur budget in the marine boundary layerbudget in the marine boundary layer
Becky Alexander, Rokjin Park, Daniel J. Jacob, Robert M. Yantosca
Harvard University, Department of Earth and Planetary Sciences
Joël Savarino, Charles. C.W. Lee, Mark H. Thiemens
University of California, San Diego, Department of Chemistry and Biochemsitry
Mian Chin
NASA Goddard Space Flight Center
AGU, Fall 2003
Mass-Dependent FractionationMass-Dependent Fractionation
-60
-40
-20
0
20
40
60
-100 -80 -60 -40 -20 0 20 40 60 80 100
18O
17O
SMOWRain and Cloud Water
Basaltic and Sedimentary Rocks
-80
-60
-40
-20
0
20
40
60
80
-100 -80 -60 -40 -20 0 20 40 60 80 100
18O
17O
Starting O2
Experimental:
O + O2 O3*Thiemens and Heidenreich 1983
Residual O2
Product O3
Measured: Tropospheric O3
Mass-Independent Fractionation:
17O/18O1
Mass-Independent FractionationMass-Independent Fractionation
Mass-Dependent Fractionation:
17O/18O0.5
17O 30‰
Mass-Independent Fractionation:
17O=17O-0.5*18O
Source ofSource of 1717OO SulfateSulfate
SO2 in isotopic equilibrium with H2O :
17O of SO2 = 0 ‰
1) SO2 + O3 (17O=30-35‰) 17O ~ 8-9 ‰
17O of SO42- a function relative amounts of OH, H2O2, and O3 oxidation
Savarino et al., 2000
3) SO2 + OH (17O=0‰) 17O = 0 ‰
2) SO2+ H2O2 (17O=1-2‰) 17O ~ 0.5-1 ‰ Aqueous
Gas
Aqueous versus Gas Phase OxidationAqueous versus Gas Phase Oxidation
Biological regulation of the climate?
(Charlson et al., 1987)
DMSOH
NO3 SO2 H2SO4OH
New particle formation
CCN
H2O2
Light scattering
Gas-phaseAqueous-phase
Aqueous-phase
O3
pH dependency of OpH dependency of O33 oxidation and its oxidation and its
effect on 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
Pre-INDOEX Jan. 1997 INDOEX March 1998
INDOEX cruises – INDOEX cruises – 1717O sulfateO sulfate
•Sulfate collected on front deck with a High Volume Air Sampler
•Collection time of ~48 hours per sample
•Laboratory conversion: SO42- O2
•Triple isotope mass-spectrometer (17O, 18O)
GEOS-CHEMGEOS-CHEM
• Global 3-D model of atmospheric chemistry and transport
•4ºx5º horizontal resolution, 26-30 layers in vertical
• Driven by assimilated meteorology
•Off-line sulfur chemistry (uses monthly mean OH and O3 fields from a coupled chemistry/aerosol simulation)
•Includes aqueous and gas phase chemistry:
S(IV) + OH (gas-phase)
S(IV) + O3/H2O2 (in-cloud, pH=4.5)
S(IV) + O3 (sea-salt aerosols, function of sea-salt
alkalinity flux to the atmosphere)Modeled after results from Chamedies and Stelson (1992)
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=0.85‰
S(IV) + O3 (in cloud, sea-salt) 17O=8.75‰
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
Pre-INDOEX Sagar Kanya Cruise #120Pre-INDOEX Sagar Kanya Cruise #120
January 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
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 Sagar Kanya Cruise #133INDOEX Sagar Kanya Cruise #133
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
Effect of sea-salt chemistry on SOEffect of sea-salt chemistry 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):
Aqueous versus Gas Phase OxidationAqueous versus Gas Phase Oxidation
Biological regulation of the climate?
(Charlson et al., 1987)
DMSOH
NO3 SO2 H2SO4OH
New particle formation
CCN
H2O2
Light scattering
Gas-phaseAqueous-phase
Aqueous-phase
O3
ConclusionsConclusions
•Sulfate17O provides information on relative oxidation pathways (gas OH versus aqueous O3,H2O2) in the atmosphere
•Measurements from INDOEX show that O3 oxidation is an important mechanism for sulfate formation over the ocean
•The magnitude and trend of 17O sulfate can be represented in the GEOS-CHEM model only with the addition of chemical formation in sea-salt aerosols
•Sulfate17O measurements provide an additional constraint for chemical transport models improve our understanding of sulfur chemistry and the sulfur budget
AcknowledgementsAcknowledgements
Funding:
Measurements: NSF
Modeling: NASA
NOAA CGC Postdoctoral Fellowship (B. Alexander)
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