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Out-of-state and Natural Contributions to Baseline Atmospheric Mercury Deposition in Alaska Krish Vijayaraghavan, Jaegun Jung and Ralph Morris ENVIRON.

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Presentation on theme: "Out-of-state and Natural Contributions to Baseline Atmospheric Mercury Deposition in Alaska Krish Vijayaraghavan, Jaegun Jung and Ralph Morris ENVIRON."— Presentation transcript:

1 Out-of-state and Natural Contributions to Baseline Atmospheric Mercury Deposition in Alaska Krish Vijayaraghavan, Jaegun Jung and Ralph Morris ENVIRON International Corporation Novato, CA Alaska Forum on the Environment Anchorage, AK February 6,

2 Acknowledgments 2 Donlin Gold U.S. Environmental Protection Agency State of Alaska Harvard University Dr. Lyatt Jaeglé, U. Washington, Seattle

3 Why is Mercury Important in Alaska? 3 Naturally found in Earth’s crust Trace amounts in fossil fuels and mine deposits Potential concerns with mercury: – Exposure to inorganic mercury in the air – Exposure to organic mercury in fish and mammals Health benefits from eating fish and marine mammals – State of Alaska: Risk v. Benefit approach for eating fish Important to consider all potential sources of mercury in Alaska including atmospheric deposition

4 What is Atmospheric Mercury Deposition? 4 Removal of mercury from the air to the ground Wet deposition – Removal in rain and snow – Depends on precipitation and mercury concentration Dry deposition – Removal by settling or molecular diffusion to the ground – Depends on land cover, winds and other weather conditions Different forms of mercury exhibit different deposition characteristics

5 Forms of Mercury and Deposition 5 Gaseous Elemental Mercury Hg(0) – Not removed from the air in rain or snow – Removed in dry conditions but also re-emitted – Transported around the world Gaseous Oxidized Mercury Hg(II) – Rapidly removed from the air by wet and dry deposition – Deposited locally and regionally Particulate-bound Oxidized Mercury Hg(p) – Properties are between those of the two gaseous forms. Organic mercury MeHg – Very little in air, instead formed in water/sediment – Methylation depends on local conditions such as sulfates – Bioaccumulates in fish and mammals

6 Mercury Cycle (simplified) 6 MeHg Re-emission Dry Deposition Wet Deposition Dry and Wet Deposition Throughfall and Litterfall Inorganic Hg MeHg Sediment Water Snow/Ice Deposition Re-emission Long Range Transport of mercury For illustrative purposes only Transformations among forms of mercury Mercury Inorganic Hg

7 Baseline Level of Mercury Deposition 7 Baseline = “Background” or “Current” level No standards for mercury deposition (unlike air concentrations) The baseline deposition level needs to be quantified to assess the additional impacts of projects in Alaska Baseline = Wet + Dry deposition due to existing sources (defined here for time period) Need to assess all sources of mercury contributing to the baseline – Man-made sources within and outside Alaska – Natural sources within and outside Alaska

8 Worldwide Sources of Atmospheric Mercury 8 Man-made sources – Fossil fuel-fired utilities (e.g., coal burning) – Mining – Waste incineration – “Legacy” man-made sources – Other sources Natural sources – Volcanoes – Mercuriferous belt (mostly cinnabar) – Off-gassing from water, soil, vegetation – Wildfires (includes previous man-made and natural)

9 Man-made Mercury Sources 9 Alaska man-made mercury emissions = 110 lb/yr (2008 U.S. National Emissions Inventory) – 71% fossil fuel combustion – 13% other industrial processes – 5% waste disposal U.S. total man-made mercury emissions = 61 ton/yr (2008 U.S. NEI) – Alaska man-made = 0.1% of US total Worldwide man-made Hg emissions = 2000 ton/yr (Pacyna et al., 2010)

10 Out-of-state Contributions to Alaska 10 Elemental mercury has very long residence time in air Arctic air mass moves air pollution around the globe Mercury emitted in Asia and Europe transported to North America (and Alaska in particular) – e.g., Coal burning power plants in China, Wildfires in Siberia Elemental mercury converted to other forms which wash out or dry deposit over Alaska. – For example, Atmospheric Mercury Depletion Events (AMDE) during spring near Barrow

11 Mercury from Wildfires 11 (Figure source: Alaska Division of Forestry)

12 Mercury from Wildfires 12 Mercury in tree needles and leaves due to previously deposited mercury from man-made and natural sources Elemental and particulate mercury released in fires Alaskan wildfire mercury emissions: average 12 tons/year (from NCAR), Vary widely Wildfire locations in 2008 from satellite data

13 Mercury from Volcanoes 13 Veniaminof volcano (Figure source: Alaska Volcano Observatory)

14 Mercury from Volcanoes 14 Mercury emitted from volcanoes: gaseous elemental and particulate Mercury emissions estimated by scaling with sulfur dioxide emissions from volcanoes from satellite data Volcano mercury emissions in Alaska in 2008 = 29 tons/year

15 Other Sources of Atmospheric Mercury 15 Mercury-containing minerals like cinnabar Off-gassing from soil, vegetation and water – Emission from water (e.g., oceans) saturated with mercury “Legacy source” of past man-made emissions which have accumulated in soils and deep oceans and are later released Deposited mercury re-emitted to atmosphere as elemental mercury, e.g., from snow Difficult to distinguish between “re-emission” of previously deposited mercury and direct natural emissions

16 Global Mercury Emissions Inventory 16 Global natural emissions ~ 4000 tons/year (includes recycled man- made) Total global mercury emissions ~ 6000 tons/year Global man-made emissions ~ 2000 tons/year* Asia Oceania Africa S. America Russia Europe North America Source: Pacyna et al., 2010 and EPA Mercury Rule

17 Mercury Deposition Monitoring in Alaska  Mercury wet deposition measured at 5 stations in the Mercury Deposition Network (MDN) by Alaska DEC and others 3 Active stations (as of 2013) Unalaska Dutch Harbor Kodiak island Gates of Arctic NP 2 Inactive stations Ambler Bartlett Cove Kodiak island – most complete data among the stations

18 Global Mercury Modeling 18 – Long range transport => Global modeling required – Global chemical transport model used = GEOS-Chem – Mercury air concentrations and wet and dry deposition in 2008 – 4 o x 5 o horizontal grid spacing; vertically up to stratosphere – Worldwide man-made and natural mercury emissions – Used to estimate contributions of continents and various source categories to mercury deposition in Alaska

19 Total Baseline Mercury Deposition 19 Wet + Dry Deposition Units = micrograms per sq. meter Yellow and Red => Higher deposition Deposition in Alaska much less than most of US Modeled annual wet deposition at Kodiak island (4.4  g/m 2 ) compares reasonably well with measurement by Alaska DEC (5.2) Note different color scales

20 Percent Contribution to Alaska Baseline Mercury Deposition from Some Key Sources 20 Asia man-made (max = 26%) Europe man-made (max = 5%) Natural sources (max = 34%) N. America man-made (max = 4%) (Note different color scales) (note: violet color is ~34%)

21 Average Contribution to Alaska Baseline Mercury Deposition 21 Natural sources Wildfires Asia man-made N. America man-made Europe man-made Other current man-made Legacy of past man-made

22 Summary 22 Mercury found naturally in the Earth’s crust and associated with some ore deposits and fossil fuels To understand the additional impact of any project in Alaska, need to first estimate the baseline (current) mercury deposition in Alaska Modeling shows that contributors of baseline mercury deposition in Alaska include (from largest to smallest): – Natural sources such as land, volcanoes, vegetation, water – Legacy of past man-made sources (accumulated in soils and deep oceans) – Man-made sources from Asia – Man-made sources from other countries and the U.S. Large contribution from out-of-state and natural sources

23 Questions 23 Krish Vijayaraghavan ENVIRON International Corporation


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