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Transcript of Marine biogenic emissions, sulfate aerosol formation, and climate: Constraints from oxygen isotopes...
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