Building a Global Modeling Capability Building a Global Modeling Capability for Mercury with GEOS-CHEMfor Mercury with GEOS-CHEM

Noelle Eckley SelinNoelle Eckley Selin

EPS DayEPS Day12 March 200512 March 2005

THE MERCURY CYCLE: CURRENT

Wet & DryDeposition 2600

ATMOSPHERE5000

SURFACE SOILS1,000,000 OCEAN

289,000

NetWet & DryDeposition1900

Net Oceanic Evasion

1500

Net burial200

Land emissions1600

Quantities in Mg/yearUncertainty ranges in parenthesesAdapted from Mason & Sheu, 2002

AnthropogenicEmissions 2400

Extraction from deep reservoirs2400

River200

(1800-3600) (700-3500)(1680-3120)

(1680-3120)

(1300-2600)(700-3500)

Hg0

1.7 ng/m3

GaseousPhase

AqueousPhase Hg0

Henry’s Constant 0.11 M/atm

Particulate Phase

Oxidation Hg2+

10-200 pg/m3

HgP

1-100 pg/m3

Hg2+

k=8.7(+/-2.8) x 10-14 cm3 s-1 (Sommar et al. 2001)k=9.0(+/-1.3) x 10-14 cm3 s-1(Pal & Ariya 2004)

k=3(+/-2) x 10-20 cm3 s-1 (Hall 1995)Reported rate constants up to k=1.7 x 10-18 cm3 s-1

Henry’s Constant 1.4x106 M/atm

OH

O3

Oxidation

HO2

??Reduction

SO3

k=1.1-1.7 x 104 M-1 s-1 (Pehkonen & Lin 1998)Shouldn’t occur (Gårdfeldt & Jonsson 2003)

k=0.0106 (+/- 0.0009) s-1

(vanLoon et al. 2000)Occurs only where high sulfur, low chlorine

Oxalate?

What does this mean for global modeling?What does this mean for global modeling?

• Use observations from latitudinal gradient, seasonal cycles, and short-term variability to constrain uncertainties

• Potential for application of inverse modeling? (Chris Holmes…)

• GEOS-CHEM simulation– Oxidation reactions: “best guess” from the published

literature– Aqueous reduction: photochemically mediated, fixed

reaction rate, proportional to [OH](g)

ATMOSPHERE

Hg04260

Hg(II)(trop.)280

Via OH:10236Via OH:10236

Dry Deposition

Ocean Emissions

Land (Natural) Emissions

Anthropogenic Emissions

Land Re-emissions

Hg(P)2

775775 204204

Via O3: 2377Via O3: 2377

1500150014461446

500500

20002000

Dry DepositionWet Deposition

Wet Deposition

10411041

53275327

191191

1111

MERCURY BUDGET IN GEOS-CHEM

Inventories in MgRates in Mg/yr

k=8.7 x 10-14 cm3 s-1

k=3 x 10-20 cm3 s-1

τ = 0.77 yr τ = 7 days τ = 3.5 daysNet ox: 5489

Reduction7124

TGM: Model vs. MeasurementsTGM: Model vs. Measurements

+

Continental sources in South America?Cruise data in the Pacific – inconsistent with OkinawaUnderestimate of concentrations over the oceans

Comparing Model with Measurements: Comparing Model with Measurements: Hemispheric Average TGMHemispheric Average TGM

• Ratio of NH/SH in measurements: 1.49 +/- 0.12 (Temme et al. 2003)

• Northern hemisphere average measurement ≈ 1.7 ng/m3

• Northern hemisphere average GEOS-CHEM: 1.62 ng/m3

• Ratio of NH/SH in GEOS-CHEM simulation: 1.5– Shows that Hg lifetime in GEOS-CHEM is realistic

Temme et al. 2003: black dots GEOS-CHEM: red line

Mace Head

0

0.5

1

1.5

2

2.5

1 2 3 4 5 6 7 8 9 10 11 12Month

TGM

(ng/

m3)

MeasuredModeled

Delta

1.451.5

1.551.6

1.651.7

1.751.8

1.851.9

1.95

1 2 3 4 5 6 7 8 9 10 11 12Month

TGM

(ng/

m3)

MeasuredModeled

St. Andrew

0

0.5

1

1.5

2

2.5

1 2 3 4 5 6 7 8 9 10 11 12

Month

TGM

(ng/

m3)

MeasuredModeled

Rörvik

0

0.5

1

1.5

2

2.5

1 2 3 4 5 6 7 8 9 10 11 12

Month

TGM

(ng/

m3)

MeasuredModeled

Alert

0

0.5

1

1.5

2

2.5

1 2 3 4 5 6 7 8 9 10 11 12

Month

TGM

(ng/

m3)

MeasuredModeled

Kejimkujik

0

0.5

1

1.5

2

2.5

1 2 3 4 5 6 7 8 9 10 11 12

Month

TGM

(ng/

m3)

MeasuredModeled

Cheeka Peak

0.000.200.400.600.801.001.201.401.601.802.00

1 2 3 4 5 6 7 8 9 10 11 12Month

TGM

(ng/

m3)

MeasuredModeled

Cape Point

0

0.2

0.4

0.60.8

1

1.2

1.4

1.6

1.8

1 2 3 4 5 6 7 8 9 10 11 12Month

TGM

(ng/

m3)

MeasuredModeled

Okinawa

0

1

2

3

4

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29

Day (April 2004)

Hg0

(ng/

m3)

Measured

Modeled

Mt. Batchelor

1.5

1.6

1.7

1.8

1.9

2

2.1

2.2

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29

Day (April 2004)

Hg0

, ng/

m3

MeasuredModeled

Data from Dan Jaffe

Banic et al. 2003: aircraft measurements ofHg0 over Ontario

Vertical Profiles of Mercury

GEOS-CHEM:Vertical profile over Ontario

GEOS-CHEM: Latitudinal average Hg0

Hg(II) in the stratosphere?Hg(II) in the stratosphere?

Supported by preliminary aircraftMeasurements…

Wet Deposition: Model vs. MeasurementsWet Deposition: Model vs. Measurements

Wet Depo. over United States, Modeled v. Measured

y = 2.1504x - 6.5583R2 = 0.7701

0

10

20

30

40

50

0 5 10 15 20 25

Measured Wet Dep, ug/m2/a

Mod

eled

wet

dep

, ug

/m2/

a

High Hg deposition in tropical regions;Gradient with latitude

Overestimate of deposition:Too much Hg(II)

Future plans for GEOS-CHEM Hg simulationFuture plans for GEOS-CHEM Hg simulation

• Land and ocean re-emission parameterization: tracing emissions from source to receptor

Source Region

Chemistry and Deposition

Land or Ocean Surface

Reemission

ReceptorRegion

Emissions“tagged” bysource andregion

Deposition“tagged” bysource andregion

Source tag maintained throughdeposition and reemission process

Ocean emissions model: collaboration with Sarah Strode, Lyatt Jaegle @ Univ. of Washington

Old Mercury920,000 preindustrial 80,000 postindustrial

New Mercury

Wet and Dry Deposition

Historical DepositionEmissions Emissions

“Old Mercury” soil concentrations initialized based on historical deposition patterns of natural, anthropogenic sources

Quantities in Mg

Re-emission Modeling in GEOS-CHEMRe-emission Modeling in GEOS-CHEM

Lifetime of “old mercury”: about 1000 yrs

Lifetime of “new mercury: weeks to months

Future Plans: “Mercury Depletion Future Plans: “Mercury Depletion Events” (MDEs) in the ArcticEvents” (MDEs) in the Arctic

• Episodic depletion of TGM at polar sunrise

• Correlates with Arctic O3 depletion events

• Mechanism: conversion to Hg(II) and subsequent deposition

• Proposed mechanism: reaction with BrO?

AMAP, 2003

Changing Contaminant PathwaysChanging Contaminant Pathways

AMAP, 2003

Incoming solar radiation Precipitation

(Rain/Snow)

Ice Cover and gas exchange

Air transport patterns

Collaborators/AcknowledgmentsCollaborators/Acknowledgments

• Advisor: Prof. Daniel Jacob• Rokjin Park• Sarah Strode & Lyatt Jaegle @ Univ. of

Washington• Chris Holmes• Bob Yantosca

Anthropogenic SourcesAnthropogenic Sources

Source: Pacyna and Pacyna, 2002

Historical Record of Mercury from Historical Record of Mercury from Ice CoreIce Core

• Pre-industrial concentrations indicate natural source

• Episodic volcanic input

• Mining emerges• Industrialization, and

recent decrease

Source: USGS

New vs. Old MercuryNew vs. Old Mercury

Source: Hintelmann et al. 2002