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Milcent data: Alexander, Savarino and Thiemens, unpublished data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