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Source-attribution for atmospheric mercury deposition:Where does the mercury in mercury deposition come from?

Dr. Mark CohenNOAA Air Resources Laboratory

Silver Spring, Maryland, mark.cohen@noaa.gov

http://www.arl.noaa.gov/ss/transport/cohen.html

Presentation given via speakerphone to a meeting of the Mercury Working Group, Office of Air Quality,

Indiana Department of Environmental Management (IDEM)April 21, 2005

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For mercury, how important is atmospheric deposition relative to other loading pathways?

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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?

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modeling the fate and transport

of atmosphericmercury

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CLOUD DROPLET

cloud

PrimaryAnthropogenicEmissions

Reactive Gaseous Mercury: RGM

Elemental Mercury: Hg(0)

Particulate Mercury: Hg(p)Atmospheric Fate Processes for Hg

Dry and Wet Deposition

Hg(0) oxidized to dissolvedRGM by O3, OH, HOCl, OCl-

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

Re-emission of natural AND previously depositedanthropogenic mercury

Adsorption/desorptionof Hg(II) to/from soot

Hg(p)

“DRY” (low RH)ATMOSPHERE:

Hg(0) oxidized to RGMby O3, H202, Cl2, OH, HCl

Polar sunrise“mercury depletion events”

Br

Upper atmospherichalogen-mediatedheterogeneous oxidation?

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some illustrative modeling

results

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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

The impact of any given mercury emissions source on any receptor is highly variable, both in space and in time

Think about the weather and then add in all the chemistry and physics of mercury’s interactions with the weather

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The impact of any given mercury emissions source on any receptor is highly dependent on the “type” of mercury emitted

Elemental mercury - Hg0 - is not readily dry or wet deposited, and its conversion to ionic Hg or Hg(p) is relatively slow

Particulate mercury – Hg(p) - is moderately susceptible to dry and wet deposition

Ionic mercury – also called Reactive Gaseous Mercury or RGM – is very easily dry and wet deposited

Conversion of RGM to Hg0 in plumes?

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0.1o x 0.1o subgrid for near-field analysis

sourcelocation

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13

14

15

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Estimated Speciation Profile for 1999 U.S.Atmospheric Anthropogenic Mercury Emissions

Very uncertain for most sources

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Each type of source has a very different emissions speciation profile

Even within a given source type, there can be big differences – depending on process type, fuels and raw materials, pollution control equipment, etc.

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Estimated 1999 U.S. Atmospheric Anthropogenic Mercury Emissions

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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]

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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

depo

sitio

n flu

x (u

g/m

2-yr

)

Hg(II) emit, 50 mHg(II) emit, 250 mHg(II) emit, 500 mHg(p) emit; 250 mHg(0) emit, 250 m

Source at Lat = 42.5, Long = -97.5; simulation for entire year 1996 using archived NGM meteorological data

Deposition flux within different distance ranges from a hypothetical 1 kg/day source

Hypothesized rapid reduction of Hg(II) in plumes? If true, then dramatic impact on modeling results…

There can be large local and regional impacts

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0 500 1000 1500 2000 2500 3000

distance range from source (km)

0%

20%

40%

60%

80%

100%

cum

ulat

ive

frac

tion

depo

site

d Hg(II) emit, 250 mHg(p) emit, 250 mHg(0) emit, 250 m

Source at Lat = 42.5, Long = -97.5; simulation for entire year 1996 using archived NGM meteorological data

Cumulative fraction deposited out to different distance ranges from a hypothetical source

250 km

At the same time, medium to long range transport can’t be ignored

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There are a lot of sources…

Large spatial and temporal variations

Each source emits mercury forms in different proportions

A lot of different sources can contribute significant amounts of mercury through atmospheric deposition to any given receptor

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

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Getting the source-apportionment information we all want is difficult

With measurements alone, generally impossible

Coupling measurements with back-trajectory analyses yields only a little information

Comprehensive fate and transport modeling – “forward” from emissions to deposition – holds the promise of generating detailed source-receptor information

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11/0111/02

11/0311/04

11/0511/06

11/0711/08

11/0911/10

11/1111/12

11/1311/14

11/1511/16

day (1999)

0

20

40

60

80

100

120

conc

entr

atio

n (p

g/m

3)

Measured Modeled (background = 0) Modeled (with background)

Comparison of measured vs. modeled TPMZingst

There are a lot of uncertainties in current comprehensive fate and transport models... Nevertheless, many models seem to be performing reasonably well, i.e., are able to explain a lot of what we see

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somesource-receptorresults for the Great Lakes

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Cohen, M., Artz, R., Draxler, R., Miller, P., Poissant, L., Niemi, D., Ratte, D., Deslauriers, M., Duval, R., Laurin, R., Slotnick, J., Nettesheim, T., McDonald, J. “Modeling the Atmospheric Transport and Deposition of Mercury to the Great Lakes.” Environmental Research 95(3), 247-265, 2004.

Note: Volume 95(3) is a Special Issue: "An Ecosystem Approach to Health Effects of Mercury in the St. Lawrence Great Lakes", edited by David O. Carpenter.

Note: results in this paper are for 1996;

Results shown in the following slides have been updated to 1999

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Emissions sources which are among the top-25 model-estimated contributors to

one or more of the Great Lakes

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Geographical Distribution of 1999 Direct Deposition Contributions to Lake Michigan

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0 - 100100 - 200

200 - 400400 - 700

700 - 10001000 - 1500

1500 - 20002000 - 2500

> 2500

Distance Range from Lake Michigan (km)

0

10

20

30

40

50

Em

issi

on

s (m

etri

c to

ns/

year

)

0

1

2

3

4

5

Dep

osi

tio

n F

lux

(ug

/m2-

year

)

Emissions Deposition Flux

Emissions and Deposition Contributions from Different Distance Ranges Away From Lake Michigan

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Top 25 Contributors to 1999 Hg Deposition Directly to Lake Michigan

Pleasant PrairieJoliet 29

J.H. CampbellWaukegan

MARBLEHEAD LIME CO.Will County

JERRITT CANYON LWD

South Oak CreekPowerton

Superior Special ServicesCLARIAN HEALTHCrawfordR.M. Schahfer Joliet 9Rockport

Marblehead Lime (South Chicago)BALL MEMORIAL FiskState LineEdgewaterVULCAN MCCOOK LIMEMonroe Power PlantMonticelloParkview Mem. Hosp.

WI IL

MI IL IL IL NV KY WI IL WI IN IL IN IL IN IL IN IL IN WI IL MI TX IN

0% 20% 40% 60% 80%

Cumulative Fraction of Hg Deposition

0

5

10

15

20

25

Ra

nk

coal-fired elec gen

other fuel combustion

waste incineration

metallurgical

manufacturing/other

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source-attribution –

the “big picture”

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Freemont Glacier, Wyoming

source: USGS, Shuster et al., 2002

Natural vs. anthropogenicmercury?

Studies show that anthropogenic activities have typically increased bioavailable Hg concentrations in ecosystems by afactor of 2 – 10

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Average mercury accumulation rate relative to pre-industrial (1800-1850)accumulation rate in five lakes in Northern Alaska (based on sediment cores)

from Fitzgerald et al. (2005), “Modern and Historic Atmospheric Mercury Fluxes in Northern Alaska: Global Sources and Arctic Depletion” Environ Sci Tech 39, 557-568

Hg flux / pre-industrial Hg flux

another example of atmospheric deposition flux increasing due to anthropogenic emissions

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What is the relative importance of global,

national, regional, and local sources?

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?

Data used by EPA to support recent Clean Air Mercury Rule

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Data from Seigneur et al. (2004) model paper

Percentage US Contribution to Deposition

10 20 30 40 50 60 70 80 90Est

imate

d T

ota

l De

posi

tion (

ug m-2

yr-1

)

0

10

20

30

40

50

60

70

r2 = 0.53

the Seigneur et al. (2004) paper shows that, for regions where deposition is high, the impact of local/regional sources is the main cause for these elevated concentrations.

(slide courtesy of Rob Mason, Univ. of CT)

[Seigneur et al., (2004), “Global Source Attribution for Mercury Deposition in the United States”, ES&T 38, 555-569.]

1999 Hg Emissions

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Results from the EPA REMSAD Mercury model

Source: slide developed by Anne Pope for the Hg Roundtable conference call April 21, 2005

Percent non-US for 1998

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Jan-96Feb-96

Mar-96Apr-96

May-96Jun-96

Jul-96Aug-96

Sep-96Oct-96

Nov-96Dec-96

0.01

0.1

1

10

100

cum

ulat

ive

depo

sitio

n (u

g H

g/m

2)

measuredmodeled

Cumulative Wet Deposition at MDN_MD_13

Modeled vs. Measured Wet Deposition at Mercury Deposition Network Site MD_13 during 1996

HYSPLIT modeling has shown thatin areas of significant local and regional anthropogenic sources,ambient measurements can be explained reasonably well by considering only these local and regional anthropogenic sources.

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For areas without large emissions sources

the deposition may be relatively low, but what deposition there is may largely come from

natural and global sources

For areas with large emissions sources

the deposition will be higher and be more strongly influenced by these large

emissions sources...

Source-apportionment answers depend a lot on where you are

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What is the relative importance of global, national, regional, and local sources?

Possible answers are emerging as our understanding improves, but

there is no scientific consensus yet...

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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

(more!) Monitoring needed for model evaluation & refinement

Many uncertainties but useful model results are emerging – these HYSPLIT model results are being extended to include global & natural emissions, and re-emissions

The question of the relative importance of global vs. national vs. regional vs. local sources is complex – the answer depends on location and on what model one is using...