Mercury in the global environment: sources and biogeochemical cycling

1. Mercury in the global environment: sources and biogeochemical cycling Daniel J. Jacob with Hannah Horowitz, Helen Amos, Anne Soerensen, Bess Corbitt, Yanxu Zhang, Elsie Sunderland and support from NSF, EPRI

2. Using models of atmospheric composition and climate to interpret observations and gain knowledge of processes Group photo (2013)

3. Presently doing way too many things Climate-chemistry-land interactions Biogeochemical cycle of mercury Next-generation of GEOS-Chem SEAC4RS aircraft campaign Chemical data assimilation and ESMs N American sources of methane Global budget of black carbon Scale issues in models Tropospheric halogen chemistry Ammonia emissions, nitrogen cycling Aerosol scavenging Deriving VOC emissions w/ satellite HCHO, CHOCHO Health effects of SE Asian fires Aerosol forcing of Arctic climate CO2-CO error correlations for inverse modeling Geostationary satellites Role of PAN In tropospheric chemistry Lightning interannual variability N American background ozone

4. Mercury in the global environment: sources and biogeochemical cycling Daniel J. Jacob with Hannah Horowitz, Helen Amos, Anne Soerensen, Bess Corbitt, Yanxu Zhang, Elsie Sunderland and support from NSF, EPRI

5. Electronic structure of mercury Mass number = 80: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 • Complete filling of subshells gives Hg(0) a low melting point, volatility • Two stable oxidation states: Hg(0) and Hg(II)

6. Biogeochemical cycle of mercury ANTHROPOGENIC PERTURBATION: fuel combustion mining WATER-SOLUBLE VOLATILE oxidation Hg(II) Hg(0) volcanoes erosion ATMOSPHERE OCEAN/SOIL Hg(0) Hg(II) particulate Hg reduction biological uptake burial uplift SEDIMENTS

7. Rising mercury in the environment Global mercury deposition has roughly tripled since preindustrial times Dietz et al. [2009]

8. Human exposure to Hg is mainly through ocean fish consumption Tuna is the #1 contributor Mercury biomagnification factor EPA reference dose (RfD) is 0.1 μg kg-1 d-1 (about 2 fish meals per week)

9. Mercury is a global pollutant Implies global-scale transport of anthropogenic emissions Anthropogenic Hg emission (2006) Hg emitted anywhere can deposit to oceans worldwide Mean Hg(0) concentration in surface air: circles = observed, background = GEOS-Chem model Transport around northern mid-latitudes: 1 month Hg(0) lifetime = 0.5-1 year Transport to southern hemisphere: 1 year Streets et al. [2009]; Soerensen et al. [2010]

10. Opened for signatures in October 2013; already signed by 91 countries • Requires best available control technology • for coal-fired power plants • Mercury mining to be banned in 15 years • Many mercury-containing commercial products to be banned by 2020 UNEP Minimata Convention on Mercury • Convention requires ratification by 50 countries to go into effect • Only ratifying country so far has been the US (November 6)

11. Historical inventory of global anthropogenic Hg emissions Large past (legacy) contribution from N. American and European emissions; Asian dominance is a recent phenomenon Streets et al. , 2011

12. 7-box model with 7 coupled ODEs dm/dt= s(t) – km where s is primary emission • Transfer rate constants k are specified from best knowledge Global biogeochemical model for mercury thermocline Primary emissions Model is initialized at natural steady state, and then forced with anthropogenic emissions for 2000 BC – present; % present-day enrichments are indicated Amos et al. [2013]

13. Characteristic time scales for Hg global biogeochemical cycle from eigenanalysis of 7-box model ~1-year time scale for exchange between atmosphere and surface/subsurface ocean; ~100-year time scale for transfer from surface reservoirs to deep ocean; ~10,000-year time scale for dissipation of perturbation to deep mineral reservoir Amos et al. [2013]

14. Time scale for dissipation of an atmospheric emission pulse Reservoir fraction • Pulse gets transferred to subsurface ocean within a few years and stays there ~100 years, maintaining a legacy in the surface ocean • Pulses injected in surface ocean or terrestrial reservoirs have similar fates Amos et al. [2013]

15. Global source contributions to Hg in present-day surface ocean emissions pre-1850 natural • Human activity has increased 7x the Hg content of the surface ocean • Half of this human influence is from pre-1950 emissions • N America, Europe and Asia share similar responsibilities for anthropogenic Hg in present-day surface ocean ROW former USSR N America S America Europe Asia Amos et al. [2013]

16. What can we hope from the Minimata Convention? Effect of zeroing global anthropogenic emissions by 2015 • Zeroing anthropogenic emissions would decrease ocean Hg by 30% by 2100, while keeping emissions constant would increase it by 40% • Elevated Hg in surface ocean will take centuries to fix; the only thing we can do in short term is prevent it from getting worse. Amos et al. [2013]

17. Observed mercury decline in/above North Atlantic Seawater Cruises Mace Head, Ireland 2008 2000 • 1990-2010 data from ship cruises show a 50% decrease over North Atlantic • Surface ocean Hg in North Atlantic also show a 50% decrease for 1990-2010, while subsurface Hg shows a 80% decrease • The atmospheric decrease can be explained by the subsurface ocean decrease 1979 1983 Mason et al. (2012) Total Hg [pM] Soerensen et al. [2012]

18. Ubiquitous mercury decline recorded in sediment cores at coastal margins of the North Atlantic Zelewski et al. (2001); Harland et al. (2000); Mansson et al. (2008); Bopp et al., Ch 26; Steinberg et al. (2004); Varekamp et al. (2003) • Observations suggest a 1950s-1970s peak in mercury discharge • Riverine inputs were then ~5 times greater than present-day. Amos et al., in prep.

19. Decreasing Hg input to subsurface North Atlantic, 1970-2000: driven by disposal of Hg-containing commercial products? 1970 2000 Disposed Hg-containing commercial products incineration Hg(II) Hg Hg wastewater, leaching N AMERICA, EUROPE Hg • Secondary wastewater treatment and phase-out of Hg from commercial products would have greatly decreased Hg input to the subsurface N Atlantic Sørensenet al., 2012

20. Importance of riverine input for ocean Hg:distinguishing between ocean basins Simulated Hg at 310 m depth in ocean MIT GCM • 70% of Hg in coastal discharges is removed by deposition to estuaries/shelf • Gulf Stream efficiently transports North American Hg across Atlantic Zhang et al., in prep.

21. Disposal of Hg in commercial products:a missing component of the Hg biogeochemical cycle? Global production of commercial Hg peaked in 1970 • Commercial Hg enters environment upon use or disposal; much larger source than inadvertent emission • Could this explain the observed environmental Hg decreases over the past two decades? Horowitz et al., in prep

22. Hg is found in many commercial products Medical Devices Wiring Devices & Industrial Measuring Devices Pharmaceuticals & Personal Care Products

23. Hg is found in many commercial products (cont.) Dyes/Vermilion Pesticides and Fertilizer Explosives/Weapons Horowitz et al., in prep

24. Tracking the ultimate environmental fate of commercial Hg Total Global Mined Hg % GDP % GDP Developed Countries Use Developing Countries Use Disposal Disposal Land Land Water Water Air Air Landfill Landfill Horowitz et al., in prep http://www.earthyreport.com/site/wp-content/uploads/2011/10/smokestack.jpg; http://www.airfields-freeman.com/TX/GreaterSW_TX_field_02.jpg; http://www.thenanfang.com/blog/wp-content/uploads/2012/07/sewage.jpg; http://www.colbond-usa.com/images/colbond-products/Geosynthetics/civil.landfills.jpeg.jpg; http://dddigitalcolour.com/wp-content/uploads/2012/10/green-recycling-symbol.jpg

25. Global historical Hg consumption Other Pesticides/Fertilizer Explosives/Weapons Dyes/Vermilion Mg yr-1of Hg Measuring & Control, Wiring Personal Care/ Pharmaceuticals Batteries Dental Medical Paint Lamps Lab/ Chemicals Silver & Large-scale Gold Mining Artisanal small-scale gold mining (ASGM) Chlor-alkali Horowitz et al., in prep

26. Fate of Hg varies with use, country, decade Example of batteries Horowitz et al., in prep

27. Fate of Hg varies with use, country, decade Example of lab chemicals Horowitz et al., in prep

28. Historical contribution of commercial Hg to environmental release Additional releases from commercial Hg in the context of atmospheric emissions Could this drive the observed environmental Hg decline? • Estimate: • “Distribution factors”: fraction of Hg entering each pathway • “Release factors”: fraction of Hg released into air, water, land Mg yr-1of Hg Landfilled Soil Water Additional Air Streets et al. (2011) mined Hg sectors Streets et al. (2011) other sectors Horowitz et al., in prep

29. Adding commercial Hg to global biogeochemical box model Atmosphere Landfills freshwater Estuaries Oceans Soils Mineral Pool Landfills, estuarine/shelf sediments are viewed as terminal sinks

30. Biogeochemical redistribution of commercial Hg after release in environment Pesticides & Fertilizer Batteries All Products 4% Release pattern, 1850-2008 Recycled 11% Mineral <1% Atmosphere <1% Estuarine Sediments 9% Atmosphere <1% Recycled 3% Atmosphere <1% Freshwater Sediments 7% Soils 16% Soils 22% Fresh Sed 10% Fate of all-time releases at year 2008 Est. Sed 8% Landfill 4% Soils 43% Ocean 23% Landfill 56% Landfill 15% Ocean 32% Ocean 35% Horowitz et al., in prep

31. Addition of commercial Hg to global biogeochemical model requires consideration of additional sinks Atmospheric mass of Hg Model with products • lkj Mg of Hg constraint from observations Model without products Horowitz et al., in prep

32. Improving the model of Hg terrestrial storage GEOS-Chem model compared to observations • Hg is bound to organic carbon; decrease ratio of Hg to C released during soil respiration from 16% to 3% (Obrist et al., 2012) • This increases the stockage of Hg in stable soil reservoirs and may help to accommodate the additional Hg from discharge of commercial products Corbitt et al., in prep