Harshita Karamchandani Placement, Masters Project and Travels…..
Mercury Source Attribution at Global, Regional and Local Scales Christian Seigneur, Krish...
-
date post
22-Dec-2015 -
Category
Documents
-
view
220 -
download
0
Transcript of Mercury Source Attribution at Global, Regional and Local Scales Christian Seigneur, Krish...
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
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
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