1 modeling the atmospheric transport and deposition of mercury dr. mark cohen noaa air resources...

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Modeling the Atmospheric Transportand Deposition of Mercury

Dr. Mark CohenNOAA Air Resources Laboratory

Silver Spring, Maryland

Mercury Workshop, Great Lakes Biennial Meeting, Kingston, Ontario, Canada June 9, 2005

1. Atmospheric mercury modeling

3. What do atmospheric mercury models need from us?

2. Why do we need atmospheric mercury models?

4. Some preliminary results for Lake Ontario

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Three “forms” of atmospheric mercuryElemental Mercury: Hg(0)

• ~ 95% of total Hg in atmosphere• not very water soluble• long atmospheric lifetime (~ 0.5 - 1 yr); globally distributed

Reactive Gaseous Mercury (“RGM”)• a few percent of total Hg in atmosphere• oxidized mercury: Hg(II)• HgCl2, others species?• somewhat operationally defined by measurement method• very water soluble• short atmospheric lifetime (~ 1 week or less);• more local and regional effects

Particulate Mercury (Hg(p)• a few percent of total Hg in atmosphere• not pure particles of mercury…

(Hg compounds associated with atmospheric particulate)• species largely unknown (in some cases, may be HgO?)• moderate atmospheric lifetime (perhaps 1~ 2 weeks)• local and regional effects• bioavailability?

CLOUD DROPLET

cloud

PrimaryAnthropogenic

Emissions

Hg(II), ionic mercury, RGM

Elemental Mercury [Hg(0)]

Particulate Mercury [Hg(p)]

Re-emission of previously deposited anthropogenic

and natural mercury

Hg(II) reduced to Hg(0) by SO2 and sunlight

Hg(0) oxidized to dissolved Hg(II) species by O3, OH,

HOCl, OCl-

Adsorption/desorptionof Hg(II) to/from soot

Naturalemissions

Upper atmospherichalogen-mediatedheterogeneous oxidation?

Polar sunrise“mercury depletion events”

Br

Dry deposition

Wet deposition

Hg(p)

Vapor phase:

Hg(0) oxidized to RGM and Hg(p) by O3, H202, Cl2, OH, HCl

Multi-media interface

Atmospheric Mercury Fate Processes

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NOAA HYSPLIT MODEL

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0.1o x 0.1o subgrid for near-field analysis

sourcelocation

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0.1o x 0.1o subgrid for near-field analysis

sourcelocation

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0 - 15 15 - 30 30 - 60 60 - 120 120 - 250

distance range from source (km)

0.001

0.01

0.1

1

10

100

hyp

oth

etic

al 1

kg

/da

y so

urc

ede

posi

tion

flux

(ug/

m2-

yr)

for Hg(II) emit

Hg(p) emitHg(0) emit

Logarithmic

Why is emissions speciation information critical?

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0 - 15 15 - 30 30 - 60 60 - 120 120 - 250


0

10

20

30

40

hyp

oth

etic

al 1

kg

/da

y so

urc

ede

posi

tion

flux

(ug/

m2-

yr)

for Hg(II) emit


Linear


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0 - 15 15 - 30 30 - 60 60 - 120 120 - 250


0

10

20

30

40

hyp

oth

etic

al 1

kg

/da

y so

urc

ede

posi

tion

flux

(ug/

m2-

yr)

for Hg(II) emit


Linear

Logarithmic

0 - 15 15 - 30 30 - 60 60 - 120 120 - 250


0.001

0.01

0.1

1

10

100

hyp

oth

etic

al 1

kg

/da

y so

urc

e

deposi

tion f

lux

(ug/m

2-y

r) f

or Hg(II) emit


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Geographic Distribution of Largest Anthropogenic Mercury Emissions Sources in the U.S. (1999) and Canada (2000)

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coal elec gen (GL_states)57.7%waste incin (GL_states)

21.0%

other fuel (GL_states)8.1%

manuf/other (GL_states)4.3%

metals (GL_states)0.8%

coal elec gen (GL_provinces)1.7%

waste incin (GL_provinces)2.1%

other fuel (GL_provinces)1.0%

manuf/other (GL_provinces)1.3%

metals (GL_provinces)2.1%

Emissions of Ionic Mercury (RGM) from Different AnthropogenicSource Sectors in Great Lakes States and Provinces (~1999-2000)

[Total RGM emissions = 13.4 metric tons/year]

Why do we need atmospheric mercury models?

to get comprehensive source attribution information --- we don’t just want to know how much is depositing at any given location, we also want to know where it came from…

to estimate deposition over large regions, …because deposition fields are highly spatially variable, and one can’t measure everywhere all the time…

to estimate dry deposition

to evaluate potential consequences of alternative future emissions scenarios

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EmissionsInventories

MeteorologicalData

Scientific understanding ofphase partitioning, atmospheric chemistry, and deposition processes

Ambient data for comprehensive model evaluation and improvement

What do atmospheric mercury models need?

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some challenges facing mercury modeling

emissions inventories

• need all sources

• accurately divided into different Hg forms

• U.S. 1996, 1999, 2003 / CAN 1995, 2000, 2005

• temporal variations (e.g. shut downs)

meteorological data

• precipitation not well characterized

scientific understanding

• what is RGM? what is Hg(p)?

• accurate info for known reactions?

• do we know all significant reactions?

• natural emissions, re-emissions?

ambient data for model evaluation

• Mercury Deposition Network (MDN) is great, but:

• also need RGM, Hg(p), and Hg(0) concentrations

• also need data above the surface (e.g., from aircraft)

• also need source-impacted sites (not just background)

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0 50 100 150 200 250 300 350

day of year

0

10

20

30

40

50

60

70

80

90

100

ug/m

2-ye

ar if

dai

ly d

ep c

ontin

uted

at

sam

e ra

te

daily value

weekly average

Illustrative example of total deposition at a location~40 km "downwind" of a 1 kg/day RGM source

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• U.S. 1996, 1999, 2003 / CAN 1995, 2000, 2005


meteorological data












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• U.S. 1996, 1999, 2003 / CAN 1995, 2000, 2005


meteorological data












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• U.S. 1996, 1999, 2003 / CAN 1995, 2000, 2005


meteorological data












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1 7 13 19 25 31 37 43 49

week of 1996

0.01

0.1

1

10

cum

ula

tive

wet

dep

os

itio

n (

ug

/m2)

measured

modeled

Comparison of Modeled vs. Measured Cumulative Wet Depositionat Underhill Center, VT during 1996

05-Feb-96 05-Apr-96 04-Jun-96 03-Aug-96 02-Oct-96 01-Dec-96 30-Jan-97

0

500

1000

1500

2000cu

mul

ativ

e H

g w

et d

epos

ition

(ng

/m2)

St. Anicet modeledSt. Anicet measured

Sites with 1996 mercury wet deposition data in the Great Lakes region

Seem to be getting reasonable results near Lake Ontario, but need to do much more evaluation…

Maybe we just got lucky!

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Where does the mercury come from that’s deposited directly onto Lake Ontario?

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Fraction of total Modeled depositionContributed by aParticular source

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American Ref-Fuel (Niagara) Homer City

KeystoneNiagara Falls Incin.NANTICOKE TGS

Phoenix ServicesKMS Peel Incin.Niagara MohawkC. R. Huntley Shawville Montour Dunkirk Eastlake Mt. Storm

Toronto Sewage Sludge Incin.Bruce MansfieldMedusa CementConesville CardinalUniv. of RochesterW. H. SammisJohn E AmosJERRITT CANYONDOFASCO (Hamilton)Lubrizol Corp.

NY PA

PA NY CAN

MD CAN

NY NY PA PA NY OH WV CAN PA PA OH OH NY OH WV NV CAN OH

0% 20% 40% 60% 80%

Cumulative Fraction of Hg Deposition

0

5

10

15

20

25R

an

k

coal-fired elec gen

other fuel combustion

waste incineration

metallurgical

manufacturing/other

Top 25 Contributors to Hg Deposition Directly to Lake Ontario based on 1999-2000 U.S./Canadian emissions

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Some Next Steps

Expand model domain to include global sources

Additional model evaluation exercises ... more sites, more time periods, more variables [Measurements in Chesapeake Bay region]

Sensitivity analyses and examination of atmospheric Hg chemistry (e.g. marine boundary layer, upper atmosphere)

Simulate natural emissions and re-emissions of previously deposited Hg

Use more highly resolved meteorological data grid

Dynamic linkage with ecosystem cycling models

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Conclusions

Impacts are episodic & depend on form of mercury emitted

Source-attribution information is important

Modeling needed to get source-attribution information

Not enough monitoring data to evaluate and improve models

Many uncertainties but useful model results are emerging

Models don’t have to be perfect to give useful information

1 modeling the atmospheric transport and deposition of mercury dr. mark cohen noaa air resources...

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