1717O proxy of anthropogenic O proxy of anthropogenic influences on atmospheric influences on atmospheric reactivity: Towards model reactivity: Towards model
interpretation of the ice core recordinterpretation of the ice core recordBecky Alexander, Rokjin J. Park, Daniel J. Jacob
Harvard University
Justin McCabe and Mark H. Thiemens
University of California, San Diego
Joël Savarino
Laboratoire de Glaciologie et Geophysique de l’Environement
American Chemical Society
August 25, 2004
Source: National Ice Core Laboratory
OverviewOverview
Oxidation capacity of the atmosphere
17O sulfate
Greenland ice core record (Milcent and Site A)
GEOS-CHEM Model – What controls 17O variability in Arctic?
– How well does it agree with measurements?
Non-photochemical sulfate production in Arctic
Secondary Species
HNO3, HCHO, 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
OH
Primary Emissions
NOx, Isoprene, SO2, CH4, …
Industry
hH2O
Current knowledge of the past Current knowledge of the past oxidative capacity of the atmosphereoxidative capacity of the atmosphere
Measurements
Year AD
Year AD
1870 1890 1910 1930 1950 1970 19900
10
20
30
40
50
60
O3 (
ppb)
H2O
2 (M
)
Sigg & Neftel, 1991
Summit
0
2
4
6
1750 20001850 19501800 1900
H2O2 O3
Source ofSource of 1717OO SulfateSulfateSO2 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
Greenland, Site AGreenland, Site A
SO
42
- nss
[pp
b]
40
50
60
70
80
90
100
110
120
1680 1730 1780 1830 1880 1930 1980
Year (AD)
0
50
100
150
200
250
NO
3- [
ppb]
Alexander et al., 2004
GISP data from Mayewski et al., 1997 and NSIDC
Greenland, Site A Greenland, Site A 1717OO
Alexander et al., 2004
PIH:
17O SO42- = 1.0‰
Present: 17O SO42- = 1.9‰
Milcent + Site A Milcent + Site A 1717OO
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
1200 1300 1400 1500 1600 1700 1800 1900 2000Year (AD)
17O(‰)
nssSO42-
17 O
ns
s SO
42
- (‰
)
Milcent data: Alexander, Savarino and Thiemens, unpublished data
17Omeas = ƒOH*0‰ + ƒH2O2*0.85‰ + ƒO3*8.75‰
ƒOH + ƒH2O2 + ƒO3 = 1
GEOS-CHEM: Global 3D CTMGEOS-CHEM: Global 3D CTMhttp://www-as.harvard.edu/chemistry/trop/geos/index.html
Bey et al., 2001; Park et al., 2004, Alexander et al., 2004, manuscript in preparation
SO2H2SO4
OH New particle
formation
CCN
Light scattering
DMSOH NO3
H 2O 2
, O 3
SO42-
O3
Sea-salt aerosol
pH = 4.5
0.0 1.6 3.2 4.7 6.3 ‰
January July
GEOS-CHEM: Seasonal GEOS-CHEM: Seasonal Variability in Variability in 1717O SulfateO Sulfate
0
2
4
6
8
0 1 2 3 4
17O
sul
fate
(‰
)
H2O2 (ppbv)
HSO3-,
H2O2, O3
Northern Hemisphere PerspectiveNorthern Hemisphere Perspective
Site A (1930-1980) 1.9‰1.9‰
Alert 1.0‰1.0‰
McCabe, Savarino and Thiemens, unpublished data
Alexander et al., 2004
Arctic MeasurementsArctic Measurements
Measurements: Justin McCabe, UCSD, personal communication
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
1 2 3 4 5 6 7 8 9 10 11 12
Month
17 O
(‰
)
GEOS-CHEM
Measurements
Alert (82°N, 85°W)
Arctic Night-time ChemistryArctic Night-time Chemistry
SIV + ½ O2 SVI
Mn2+, Fe3+
17O = 0‰
??
From Sirois and Barrie, 1999
xV (ng m-3) xMn (ng m-3)
Savarino et al., 2001
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
1 2 3 4 5 6 7 8 9 10 11 12
Month
17 O
(‰
)
GEOS-CHEM
Measurements
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
1 2 3 4 5 6 7 8 9 10 11 12
Month
17 O
(‰
)
GEOS-CHEM
[Fe(III)] = 0.5 mol/l [Mn(II)] = 0.05 m/l
Measurements
Alert: Metal Catalysis?Alert: Metal Catalysis?
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
1 2 3 4 5 6 7 8 9 10 11 12
Month
17 O
(‰
)
GEOS-CHEM
[Fe(III)] = 0.5 mol/l [Mn(II)] = 0.05 m/l
[Fe(III)] = 5.0 mol/l [Mn(II)] = 0.5 m/l
Measurements
ConclusionsConclusions
17O provides first conservative constraint on anthropogenic impacts on the oxidation capacity of the
atmosphere
Need a global model to interpret quantitatively
GEOS-CHEM 17O sulfate variability in high Northern latitudes controlled by H2O2/OH concentrations in present
day. Preindustrial?
Alert measurements indicate non-photochemical source of sulfate in present day atmosphere
AcknowledgementsAcknowledgements
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