1. THE FOG SQUAD IN CALTECH YEARS (Jan 1982) “No problem too obscured” Jed WaldmanBill Munger Daniel Jacob

2. THE ROTATING ARM COLLECTOR A lethal contraption for collecting fog droplets Jed and the RAC at Pt. Reyes, Aug 1982

3. WHAT TO DO WHEN YOU’RE INEPT IN THE LAB AND IN THE FIELD? Try modeling

4. Group photo (2013) And now …using global models of atmospheric composition and climate to interpret observations and gain knowledge of processes

5. GEOS-Chem global 3-D model of atmospheric composition Satellites Surface networks Aircraft GEOS-Chem chemical transport model The GEOS-Chem user community: 70 institutions, 18 countries 7 th GEOS-Chem meeting next week at Harvard – 200 participants

6. Good reasons not to choose a career in research: Independence Joy of discovery Shielding from human suffering and stupidity Job security See the world “My experience as grad student/postdoc isn’t fun” (it doesn’t get better) “Research is too narrow, too slow-paced” “I want to become filthy rich” Bad reasons: “I’m not creative enough” “I don’t want to publish or perish” “It’s too hard to get a good job” “I want to have a personal life” Is a research career for you? …but it may not be for you. A lot has to be said for a career in research… If not you, then who?

7. Hg is present in atmosphere as an elemental gas …a property that it shares only with the noble gases! Xe KrNe Ar He Hg Rn

8. Electronic structure of mercury Mass number = 80: 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 4f 14 5s 2 5p 6 5d 10 6s 2 Complete filling of subshells gives Hg(0) a low melting point, volatility Two stable oxidation states: Hg(0) and Hg(II)

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

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

11. 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)

12. Mercury is a global pollutant Anthropogenic Hg emission Streets et al. [2009]; Soerensen et al. [2010] Transport around northern mid-latitudes: 1 month Transport to southern hemisphere: 1 year Implies global-scale transport of anthropogenic emissions Hg(0) lifetime = 0.5-1 year Hg emitted anywhere can deposit to oceans worldwide

13. Atmospheric redox chemistry of mercury: driver of mercury deposition Hg(0) Hg(II) OH, O 3, Oxidation of Hg(0) by OH or O 3 is endothermic HO 2 (aq) Older models Our current hypothesis is that oxidation by Br atoms is dominant: ? XX Cl, Br No viable mechanism identified so far for atmospheric reduction of Hg(II) X Horowitz et al., in prep

14. UNEP Minimata Convention on Mercury 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 Opened for signatures in October 2013; already signed by 128 countries Convention requires ratification by 50 countries to go into effect; 9 have ratified so far

15. 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

16. Global biogeochemical model for mercury (Amos et al., 2013) 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 Model is initialized at natural steady state, and then forced with anthropogenic emissions for 2000 BC – present; % present-day enrichments are indicated Primary emissions thermocline Observational constraints: 1.present-day atmosphere 4600-5600 Mg 2.present-day ocean 0.5-2.5 pM 3.2-5 x atmospheric increase since 1850

17. Characteristic time scales for Hg global biogeochemical cycle from eigenanalysis of 7-box model Amos et al. [2013] ~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

18. 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]

19. Global source contributions to Hg in present-day surface ocean 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 Amos et al. [2013] Europe Asia N America S America former USSR ROW pre-1850 natural emissions

20. 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]

21. Conundrum: decrease of atmospheric Hg in past two decades Circles = observations Background = GEOS-Chem model (after improvements) The decreasing trend is inconsistent with standard emission inventories Zhang et al., in prep

22. Disposal of Hg in commercial products: a missing component of the Hg biogeochemical cycle? Global production of commercial Hg peaked in 1970 Horowitz et al., 2014 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? Global Hg production Global inadvertent Hg emission [Streets et al., 2011]

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

24. Pesticides and Fertilizer Explosives/Weapons Dyes/Vermilion Hg is found in many commercial products (cont.) Horowitz et al., 2014

25. Global historical Hg consumption Horowitz et al. [2014]

26. Tracking the ultimate environmental fate of commercial Hg 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 Total Global Mined Hg Developed Countries UseDeveloping Countries Use % GDP Disposal Air Land Water Air Land Water Landfill Horowitz et al., 2014

27. Historical releases of commercial Hg to environmental reservoirs

28. Additional releases from commercial Hg in the context of atmospheric emissions Estimate: –“Distribution factors”: fraction of Hg entering each pathway –“Release factors”: fraction of Hg released into air, water, land Historical contribution of commercial Hg to environmental release Horowitz et al., 2014 Much larger source than coal combustion – how can we make it compatible with constraint on atmospheric inventory? Could it explain observed atmospheric trend?

29. Sink from sequestration of riverine Hg in coastal sediment 55 Mg a -1 of Hg is discharged to oceans from rivers, comparable to atmospheric deposition About 70% of this riverine Hg settles in estuaries and coastal sediments; long-term sink? Amos et al., 2014

30. Inclusion of shallow sediment sequestration in Hg budget

31. Ocean margin sediments: dominant natural reservoir, speeds up removal of environmental Hg without sequestration with sequestration Amos et al., 2014

32. Sequestration in ocean margin sediments speeds up effect of Minimata Convention