Mercury Source Attribution at Global, Regional and Local Scales Christian Seigneur, Krish Vijayaraghavan, Kristen Lohman, and Prakash Karamchandani AER San Ramon, California

Multi-scale Modeling of Atmospheric Mercury TEAM: continental model coarse grid CTM global model TEAM fine-scale model grid TRUE & ROME plume models

Global Emissions of Mercury (Mg/y) Total = 6402 Mg/y Anthropogenic, 2134

Anthropogenic Emissions of Mercury\ (Mg/y per 1 o x1 o grid cell)

Anthropogenic Emissions of Mercury (Mg/y) Asia Africa USA Europe World Power plants Incinerators United States Mobile Sources Non-utility coal burn Chlor-alkali Mining Other sources S. America

Atmospheric Chemistry of Mercury Gas phase Hg(0)Hg(II) Hg(p) oxidation Hg(0) Hg(II) Hg(p) oxidation reduction Aqueous phase adsorption to soot

Global Modeling of Mercury Hg(0) Concentration (ng/m 3 )

Hg Annual Deposition (  g/m 2 -y) 2004 Base Simulation

Performance Evaluation Model vs. Wet Deposition Data 30 MDN sites for annual wet deposition of mercury in 1998 R 2 = 0.55 Error = 26% Bias = +12%

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 in Emissions from Coal-fired Power Plants on TEAM Performance * 30 sites 8%11%12% Bias 24%26% Error R2 R2 67% Hg(II) reduced to Hg(0) 14% Hg(II) reduced to Hg(0) Base Case Performance Statistics*

Hg annual deposition (  g/m 2 -y) simulation with 2/3 plume Hg II reduction Lower mercury deposition in the Northeast Contribution of local & regional sources to total mercury deposition is reduced

Grid models overestimate the local impacts of point sources TRUE - Local modeling with a plume model formulation Emissions are instantaneously mixed in a large volume and vertical dispersion is overestimated

Example of TEAM gridded domain overlaid by the TRUE plume model The blue area of TRUE has the same surface area as the purple area of TEAM (278 km 2 )

Comparison of mercury deposition for TEAM and TRUE within a 278 km 2 area

Percentage of power plant emissions deposited within a 50 km radius (8000 km 2 ) *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 km 2 ) *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 O 3 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)