Mercury Source Attribution atGlobal, Regional and Local Scales

Christian Seigneur,

Krish Vijayaraghavan, Kristen Lohman,

and Prakash Karamchandani

AER

San Ramon, California

Multi-scale Modeling ofAtmospheric Mercury

TEAM: continentalmodel coarse grid

CTM global model

TEAM fine-scale model grid

TRUE & ROMEplume models

Global Emissions of Mercury (Mg/y)

Asia, 1138

Oceania, 48

Africa, 246

Natural, 1067

Reemissions, 3201

North America, 200

South America, 176

Europe, 326

Total = 6402 Mg/y

Anthropogenic,2134

Anthropogenic Emissions of Mercury\(Mg/y per 1ox1o grid cell)

-180.00 -150.00 -120.00 -90.00 -60.00 -30.00 0.00 30.00 60.00 90.00 120.00 150.00 180.00

-60.00

-30.00

0.00

30.00

60.00

0.001 to 0 .005

0.005 to 0 .010

0.010 to 0 .050

0.050 to 0 .100

0.100 to 21.000

Anthropogenic Emissions ofMercury (Mg/y)

Asia

Africa

USA

Europe

WorldWorld

Powerplants

Incinerators

United StatesUnited States

MobileSources

Non-u

tility

coal

bur

nChlor-alkaliMining

OthersourcesS. America

Atmospheric Chemistry of Mercury

Gas phase Hg(0) Hg(II) Hg(p)oxidation

Hg(0) Hg(II)

Hg(p)

Hg(p)

oxidation

reduction

Aqueous phase

adsorption to soot

Global Modeling of MercuryHg(0) Concentration (ng/m3)

Hg Annual Deposition (g/m2-y)2004 Base Simulation

Performance Evaluation Model vs. Wet Deposition Data

30 MDN sitesfor annualwet depositionof mercury in 1998

R2 = 0.55

Error = 26%

Bias = +12% 0

5

10

15

20

25

0 5 10 15 20 25

Measured (g/m2-y)

Sim

ula

ted

(g

/m2 -y

)

1:1.5 line

1.5:1 line

1:1 line

Contribution (%) of sources other than U.S. anthropogenic sources to Hg deposition

Evidence for Reduction of Hg(II) to Hg(0)in Power Plant Plumes

• 14% average reduction of Hg(II) per hour measured near Atlanta, GA (Edgerton et al., 2004; average over different seasons, from different plants, and over different travel times)

• Bowen plant in GA: Airplane measurements showed 16% reduction after 1.5 hours

• Pleasant Prairie plant in WI: Airplane measurements showed 66% reduction at a distance of 8 km

• Plume chamber experiments: 2/3 of Hg(II) reduced to Hg(0)

Effect of changing Mercury Speciation inEmissions from Coal-fired Power Plants

on TEAM Performance

* 30 sites

8%11%12% Bias

24%26%26% Error

0.570.560.55 R2

67% Hg(II) reduced to

Hg(0)

14% Hg(II) reduced to

Hg(0) Base Case

Performance Statistics*

Hg annual deposition (g/m2-y) simulation with 2/3 plume HgII reduction

•Lower mercurydeposition in theNortheast

•Contribution oflocal & regionalsources to totalmercury depositionis reduced

Grid models overestimatethe local impacts of point sources

TRUE - Local modelingwith a plume model formulation

Emissions are instantaneouslymixed in a large volume andvertical dispersionis overestimated

Example of TEAM gridded domainoverlaid by the TRUE plume model

The blue areaof TRUEhas the samesurface area asthe purple areaof TEAM(278 km2)

Comparison of mercury deposition forTEAM and TRUE within a 278 km2 area

Power plant Mercury deposition ratioTEAM/TRUE

A 2.1

B 1.8

C 2.0

D 1.8

E 1.5

Percentage of power plant emissionsdeposited within a 50 km radius (8000 km2)

% emissions deposited*Power plantTEAM TRUE

A 5% 4%

B 4% 4%

C 4% 3%

D 4% 3%

E 4% 4%

*without Hg(II) reduction; percentages could be lower with Hg(II) reduction

Calculated contributions of power plants to mercury deposition within a 50 km radius (8000 km2)

Power plant contribution*Power plantTEAM TRUE

A 10% 8%

B 6% 5%

C 3% 2%

D 1% 1%

E 1% 1%

*without Hg(II) reduction; percentages could be lower with Hg(II) reduction

Conclusions

• The multiscale modeling system reproduces well major spatial patterns in observed Hg wet deposition fluxes

• However, wet deposition is overpredicted in the Northeast in 1998

Conclusions

• There is direct and circumstantial evidence for reduction of Hg(II) to Hg(0) in power plant plumes

• Incorporating the effect of this reduction improves model performance

• Current mercury models do not account for this possible reduction and likely overestimate the impact of controls

Conclusions

• Grid models overpredict local deposition compared to plume models by a factor of ~ 2 on average because vertical dispersion of material aloft is overestimated in grid models

• Typically, less than 5% of power plant mercury emissions are deposited within a 50 km radius

• Power plants were estimated to contribute from 1 to 10%to total mercury deposition within a 50 km radius

Conclusions

• The local potential impacts of elevated point sources are better assessed by plume models than grid models; the most rigorous treatment would be to use a plume-in-grid model, such as those developed for O3 and PM

• Mercury models should be evaluated for dry deposition

• Sensitivity to uncertainties in mercury chemistry should be investigated

Acknowledgements

• Funding was provided by EPRI (Leonard Levin, Project Manager) and Southern Company (John Jansen, Project Manager)