The Atmospheric Deposition of Mercury to the Great Lakes

Dr. Mark Cohen Physical Scientist

NOAA Air Resources LaboratorySilver Spring, Maryland

Presentation at An Ecosystem Approach to the Health Effects

of Mercury in the Great Lakes BasinFebruary 26-27, 2003

Cleary International Conference CenterWindsor, Ontario

• Atmospheric Processes for Mercury

• Key questions regarding atmospheric deposition

• Methodological approaches to answer these questions

• Preliminary results of an atmospheric modeling analysis

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

PrimaryAnthropogenicEmissions

Elemental Mercury: Hg(0)

Reactive Gaseous Mercury: RGM

Particulate Mercury: Hg(p)

Atmospheric FateProcesses for Hg

Dry and WetDeposition

Hg(0) oxidized to dissolved RGM by O3, HOCl, OCl-

Hg(II) reduced to Hg(0) by SO2 and HO2

Hg(p)

“DRY” (low RH)ATMOSPHERE

Re-emissionof natural AND previouslydepositedanthropogenicmercury

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

desorptionof Hg(II) to/from soot

Halogen-mediated oxidationon the surface of ice crystals

cloud

Key questions regarding atmospheric deposition:

1. How much is being deposited in each Lake?

2. How important is direct deposition to a given lakerelative to indirect loading via deposition to thelake’s watershed?

3. How important is atmospheric deposition relative to other loading pathways (e.g., direct discharge to the Lake or its tributaries)

4. What is the relative importance of the contributionsfrom local, regional, national, continental, and global sources?

5. What is the relative importance of contributions fromdifferent types of sources, e.g, coal fired utilities,incinerators, natural emissions, etc.?

We need to know all these things to efficiently directaction to reduce the contamination levels in a given lake.

lake superiorlake huron

lake michiganlake erie

lake ontariogulf of maine

0

200

400

600

800

tota

l dep

ositi

on (k

g/ye

ar)

these preliminary modelpredictions

measurement-basedestimates (Lake Mich MassBalance, ca 1995)

Total Atmospheric Deposition Mass of Mercury

lake superiorlake huron

lake michiganlake erie

lake ontariogulf of maine

0

5

10

15

20

tota

l flu

x (g

/km

2-ye

ar)

these preliminary modelpredictions

measurement-based estimates(Lake Mich Mass Balance, ca1995)

Total Atmospheric Deposition Flux of Mercury

Estimated atmospheric deposition of mercury to the Great Lakes and the Gulf of Maine

• We don’t have data for all the lakes

• In general, insufficient measurements and modeling analysis to obtain accurate, timely estimates of this simple mass balance information for the Great Lakes

• Many uncertainties in the existing estimates,e.g., significance of watershed processing

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

Atmospheric deposition almost certainly

plays a very significantrole in the mercury

contaminationof the Great Lakes

1995 Global Hg Emissions Inventory, courtesy of Josef Pacyna, NILU,

Norway (2001)

fuel combustion

waste incineration

manufacturing/other

0.00 0.10 0.20 0.30

Emissions (grams per person per year)

United StatesCanada

U.S. emissions from a hybrid EPA inventory, representing 1996 for some sources, 1999 for othersThe Canadian emissions estimates are from an Environment Canada inventory for 1995

Per Capita Emissions of Mercury(aggregated source categories)

coal combustion, electric gen.

coal combustion, comm./ind.

natural gas comb.

oil combustion (non-mobile)

mobile sources

other fuel combustion

medical waste incin

municipal waste incin

hazardous waste incin

industrial waste incin

waste incineration, other

chloralkali

chemical manufacturing, other

metallurgical processes

mining

cement/concrete

pulp/paper

lamp manuf. and breakage

other manufacturing

other

0.00 0.05 0.10 0.15 0.20 0.25

Emissions (grams per person per year)

United StatesCanada

U.S. emissions from a hybrid EPA inventory, representing 1996 for some sources, 1999 for othersThe Canadian emissions estimates are from an Environment Canada inventory for 1995

Per Capita Emissions of Mercury

Modelevaluation

Modelevaluation

Mercury Monitoring in Ambient Air

• Mercury Deposition Network:weekly wet deposition measurements;many sites in the U.S. and Canada;data are easily available through the web

• CAMNET – Hg(0) ambient air concentrationsat a number of locations (Canada)

• While several research programs measureRGM and Hg(p), there is no systematic networkcollecting publicly accessible data for thesecompounds, analogous to the MDN.

• Unfortunate, because:• (1) they are important for dry deposition;• (2) they are needed for model evaluation

• Mercury is not included in theIntegrated Atmospheric DepositionNetwork (IADN)… (but may be soon)

We are generally not actually interested in the concentration or deposition at a single monitoring site…

We are just using the few monitoring sites that we might have to give us a clue as to what the total impact might be…

We are interested in the deposition to an entire water body, or to a particular ecosystem

There are large spatial variations in wet deposition

Source: M. Landis and G. Keeler, Atmospheric Mercury Deposition toLake Michigan during the Lake Michigan Mass Balance Study.Environmental Science and Technology 36:4518-4524, 2002

There are large spatial variations indry deposition and re-emission

Source: A. Vette, M. Landis and G. Keeler, Deposition and Emissions of Gaseous Mercury to and from Lake Michigan during the Lake MichiganMass Balance Study (July, 1994-October 1995).Environmental Science and Technology 36:4525-4532, 2002

Modelevaluation

Modelevaluation

Can’t reliably estimate the amount of deposition or source-receptor relationships using monitoring alone…

Modeling can potentially give you these answers, but

cannot be done credibly without using monitoring

to ground-truth the results

Overall Project Goal

Develop atmospheric mercury source-receptor information for the Great Lakes, the Gulf of Maine, and other selected receptors, to estimate the amount of deposition and the relative contributions of different

source regions(local, regional, national, continental, global)

source categories(e.g., coal combustion, waste incineration, etc.)

…to the atmospheric deposition to any given receptor

Overall Methodology

Start with atmospheric mercury emissions inventory

Perform atmospheric fate and transport modeling of these emissions (using a modified version of NOAA’s HSYPLIT model)

Keep track of source-receptor informationduring the modeling

Evaluate the modeling by comparison of the predictions against ambient monitoring data

If model is performing satisfactorily, report source-receptor results from the simulations

(Similar to earlier work with dioxin and atrazine)

Transfer Coefficients for Hg are strongly influenced by the “type” of Hg emitted

[Hg(II) has much greaterlocal impacts than Hg(0)]

lake superiorlake huron

lake michiganlake erie

lake ontariogulf of maine

0

200

400

600

800

tota

l dep

ositi

on (k

g/ye

ar)

these preliminary modelpredictions

measurement-basedestimates (Lake Mich MassBalance, ca 1995)

Total Atmospheric Deposition Mass of Mercury

lake superiorlake huron

lake michiganlake erie

lake ontariogulf of maine

0

5

10

15

20

tota

l flu

x (g

/km

2-ye

ar)

these preliminary modelpredictions

measurement-based estimates(Lake Mich Mass Balance, ca1995)

Total Atmospheric Deposition Flux of Mercury

Estimated atmospheric depositionof mercury to the Great Lakes

0 - 1

00

100

- 200

200

- 400

400

- 700

700

- 100

0

1000

- 15

00

1500

- 20

00

2000

- 25

00

> 25

00

Distance Range from Lake (km)

0%

5%

10%

15%

20%

25%

30%

Frac

tion

of T

otal

emissions

Percent of Total 1996 Emissions of MercuryArising From Within Different Distance Ranges From Lake Superior

(U.S. and Canadian direct anthropogenic emissions only)

0 - 1

00

100

- 200

200

- 400

400

- 700

700

- 100

0

1000

- 15

00

1500

- 20

00

2000

- 25

00

> 25

00

Distance Range from Lake (km)

0%

10%

20%

30%

40%

Frac

tion

of T

otal

emissions deposition

Percent of Total 1996 Emissions or Deposition of MercuryArising From Within Different Distance Ranges From Lake Superior

(U.S. and Canadian direct anthropogenic emissions only)

Contributions of different overall source sectorsto the atmospheric deposition of mercury in 1996

per capita flux, i.e., nanograms of mercurydeposited per km2 of lake per person per year

fuels incin. metals other0

10

20

30

40

ng/k

m2-

pers

on-y

ear U.S. Canada

Lake Michigan

“fuels" = fuel combustion;"incin." = waste incineration;

"metals" = metallurgcial processes

Some concluding observations

For the Great Lakes, atmospheric depositionof mercury is almost certainly a very significant loading pathway.

processes are complex, and there is stillmuch work to do to iron out the details…

Both monitoring and modeling must be usedtogether to answer the key questions we needanswered about atmospheric depositionof mercury to the Great Lakes

magnitude relative importancesource-receptor relationships

Preliminary results for source receptor relationshipssuggest the importance of coal-fired power plants,over at least a regional and national scales