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

Noelle Eckley Selin, Noelle Eckley Selin,

Rokjin J. Park, Daniel J. JacobRokjin J. Park, Daniel J. Jacob

• Constraining the global budget of mercury and atmospheric processes

• Providing boundary conditions for CMAQ

• Understanding the behavior of mercury in the Arctic

• Tracing pathways of intercontinental mercury pollution

• Evaluating the impact of climate change on mercury pathways

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

(1300-5400) (320-8000)(1680-3120)

(1680-3120)

(950-3800)(300-7500)

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)One measured value in literature

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

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?

• GEOS-CHEM: 2 simulations– “Original” simulation: best guess from the published

literature– “Improved” simulation: adjust oxidations to latitudinal

gradient and observations

ATMOSPHERE: 4621

Hg04272

Hg(II)347

Via OH: 2769Via OH: 2769

Dry Deposition

Ocean Emissions

Land (Natural) Emissions

Anthropogenic Emissions

Land Re-emissions

Hg(P)2

775775 204204

Via O3: 2444Via O3: 2444

1500150014461446

500500

20002000

Dry DepositionWet Deposition

Wet Deposition

22272227

36733673

160160

4343

MERCURY BUDGET IN GEOS-CHEM

Inventories in MgRates in Mg/yr

k=1.98 x 10-14 cm3 s-1

k=3 x 10-20 cm3 s-1

τ = 0.82 yr τ = 21 days τ = 3.4 days

Measured Improved GEOS-CHEM Original GEOS-CHEM

Delta, BC

0

0.5

1

1.5

2

2.5

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

Month

TG

M (

ng

/m3

)

Alert

0

0.5

1

1.5

2

2.5

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

Month

TG

M (

ng

/m3

)

Mace Head

0

0.5

1

1.5

2

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

Month

TG

M (

ng

/m3

)

Cape Point

0

0.5

1

1.5

2

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

Month

TG

M (

ng

/m3

)

St. Anciet, PQ

0

0.5

1

1.5

2

2.5

3

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

Month

TG

M (

ng

/m3

)

Pallas, Finland

0

0.5

1

1.5

2

2.5

3

3.5

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

Month

TG

M (

ng

/m3

)

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)

• Ratio of NH/SH in optimized GEOS-CHEM simulation: 1.49– Shows that Hg lifetime in GEOS-CHEM is realistic

Lamborg et al. 2002 GEOS-CHEM

TGM: Model vs. MeasurementsTGM: Model vs. Measurements

Guiyang, China:Measured: 9.00Modeled: 2.98

+

Model is high at northern midlatitudes: overestimate of sources?

Underestimate of sourcesIn Asia?

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

U.S. Mercury Deposition Network vs. GEOS-CHEM

y = 1.1368x - 0.9671

R2 = 0.7454

0

5

10

15

20

25

0 5 10 15 20 25

Measured Wet Deposition (ug/m2/yr)

Mo

de

led

We

t D

ep

os

itio

n

(ug

/m2

/yr)

High Hg deposition in tropical regions;Gradient with latitude

Overestimate of deposition:Reduction in sources needed (14%)?

Mean Seasonal Variation of TGM Concentrations at Northern Midlatitudes

0

0.5

1

1.5

2

2.5

3

Winter Spring Summer Fall

Season

TG

M (

ng

/m3

)

Measured

Modeled

Overestimate between 7-25% (depending on season): overestimate of sources?

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