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
Global budget
of black carbon
N American
sources of methane
Scale issues
in models
Ammonia emissions,
nitrogen cycling
Tropospheric
halogen
chemistry
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
VOLATILE
WATER-SOLUBLE
oxidation
Hg(0)
Hg(II)
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 = year
Transport to southern hemisphere: 1 year
Streets et al. [2009]; Soerensen et al. [2010]

10. UNEP Minimata Convention on Mercury
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
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. Global biogeochemical model for mercury
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
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
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
Europe
Asia
N America
S America
former
USSR
ROW
pre-1850
natural
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
Cruises
Mace Head, Ireland
Total Hg [pM]
Seawater
2000
2008
1979
1983
Mason et al. (2012)
data from ship cruises show a 50% decrease over North Atlantic
Surface ocean Hg in North Atlantic also show a 50% decrease for , while subsurface Hg shows a 80% decrease
The atmospheric decrease can be explained by the subsurface ocean decrease
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, : driven by disposal of Hg-containing commercial products?
Disposed Hg-containing
commercial
products
incineration
Hg(II) Hg Hg
N AMERICA,
EUROPE
wastewater,
leaching Hg
Secondary wastewater treatment and phase-out of Hg from commercial products would have greatly decreased Hg input to the subsurface N Atlantic
Sørensen et 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
Just pictures of paint
Lamps
Batteries
Split into two if necessary
Cosmetics - Products contain up to 60,000 PPM – generally >1 ppm is restricted

23. Hg is found in many commercial products (cont.)
Dyes/Vermilion
Pesticides and Fertilizer
Explosives/Weapons
Just pictures of paint
Lamps
Batteries
Split into two if necessary
Cosmetics - Products contain up to 60,000 PPM – generally >1 ppm is restricted
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
Air
Land
Water
Air
Land
Water
Recycled goes back into Hg supply. Have an arrow of that. It would be better to add the Hg supply back in to the mined amount. The recycled has to go somewhere – feeds back into Hg supply.
Now we have Hg consumption in each product: next step is where does it go. Quantifying five ultimate fates:
Landfill
Landfill
Horowitz et al., in prep

25. Global historical Hg consumption
Other
Pesticides/Fertilizer
Explosives/Weapons
Dyes/Vermilion
Mg yr -1 of Hg
Personal Care/ Pharmaceuticals
Measuring & Control, Wiring
Batteries
Dental
Medical
Paint
I HAVE PRESENTED METHODS BEFORE
INCLUDE METHODS OF HOW TO DO THIS IN THE SUPPLEMENTAL SLIDES
-fine tuning, MAIN DIFFERENCE BETWEEN THIS TIME & LAST TIME IS CHLOR ALKALI!!!!!! More consistent with global importance of chlor alkali!!
---- can touch base w/ David Kocman
--- explain what other is !!!
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
Fill in the atmosphere thing !! Light blue!
Horowitz et al., in prep

27. Fate of Hg varies with use, country, decade
Example of lab chemicals
PUT WATER INSTEAD OF SURFACE OCEAN
Think about whether I want to animate or not!
Snapshot of modern day changed really dramatically
To look in a little more detail of what is currently included in atmospheric emissions inventories and potentially missing sources to models, on the left is global anthopogenic atm. Hg emissions broken down by source process for 2008 and on the right is the consumption of primary mined Hg for Not only is the amount of Hg used in commercial applications larger than the total direct atmospheric emissions, but there is little overlap between the two inventories – notably chlor-alkali and artisanal gold mining, and waste incineration which will account for releases from the disposal of some of the products on the right chart like batteries. Even for chlor alkali and gold mining there is much more Hg used than is in the direct atmospheric emissions inventory. We can assume that all of the mined Hg used in commercial products will eventually enter the environment on a timescale and in a way that depends on the type of use. Thus, models
that only include direct atmospheric emissions are missing ,,
From wikipedia: caustic soda = lye = sodium hydroxide; chlorine used in all kinds of applications like drinking water.
“Sodium hydroxide is used in many industries, mostly as a strong chemical base in the manufacture of pulp and paper,textiles, drinking water, soaps and detergents and as a drain cleaner.”
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
Historical contribution of commercial Hg to environmental release
Could this drive the observed environmental Hg decline?
Mg yr -1 of Hg
Landfilled
Soil
Water
Make streets orangey red two tone!!!!!!!! From Mined Hg and non-Hg mined related sources!
Streets et al.
(2011)
mined Hg sectors
Additional Air
Streets et al. (2011) other sectors
Horowitz et al., in prep
Estimate:
“Distribution factors”: fraction of Hg entering each pathway
“Release factors”: fraction of Hg released into air, water, land

29. Adding commercial Hg to global biogeochemical box model
Atmosphere
Landfills
freshwater
Estuaries
Oceans
Soils
HMA: I would write “methylmercury” instead of CH3Hg – it’s more recognizeable
Hg is naturally occurring in rocks. Under the natural mercury cycle, Hg is released into the atmosphere from the lithosphere through volcanoes, outgassing, and weathering. Once in the atmosphere, Hg actively exchanges with the terrestrial and ocean surface until it is eventually buried in deep ocean sediments and returned to the lithosphere through subduction. Humans have increased the amount of Hg removed from deep stable reservoirs to be actively cycling in surface reservoirs through industry, mining, and combustion of fossil fuels. This is a cause for concern, because Hg in aquatic environments – both freshwater and oceanic - can be converted to methylmercury, which is a neurotoxin that bioaccumulates in fish. humans and wildlife are primarily exposed to this toxin by eating contaminated fish. We need to understand how much mercury in the environment and in fish is anthropogenic in origin and how it cycles through the environment in order to create policy to reduce exposure and to assess the effectiveness of proposed policies.
Mineral Pool
Landfills, estuarine/shelf sediments are viewed as terminal sinks

30. Pesticides & Fertilizer all-time releases at year 2008
Biogeochemical redistribution of commercial Hg after release in environment
Pesticides & Fertilizer
Batteries
All Products 4%
Release pattern,
Recycled
11%
Mineral
<1%
Estuarine Sediments 9%
Atmosphere
<1%
Atmosphere
<1%
Recycled 3%
Atmosphere
<1%
LANDFILLS SEQUESTER HG VERY SUCCESSFULLY
SHOW THE RELEASES FIRST
How the biogeochem cycle redistributes the Hg after its released
Add recycled
Thoughts:
- Shades of green are the overturning timescales – short to long is light to dark green; same for ocean - landfills are very effective at retaining/sequestering Hg
- Regardless of initial input distribution a large portion is retained in the subsurface ocean consistent with Helen’s results – from atmospheric emission and deposition to the ocean – all Hg entering the system must eventually go through the ocean to the deep ocean to be sequestered in sediments and buried and the timescale over which we are looking fits well with the timescale of Hg in the subsurface ocean.
Relatively more is in deep ocean for pesticides & fertilizer than for ASGM because of the temporal trajectory: Pesticides and Fertilizer were important from the 1930s to 1990s, ASGM releases are primarily in the last 2 decades and so less has had time to make it to the deep ocean relative to the subsurface ocean.
A question for my work is how important are the soils – how large are these reservoirs and how effective is the Retention of Hg in soils? How much does get reemitted back to the atmosphere.
Freshwater Sediments 7%
Soils
16%
Soils
22%
Fate of
all-time releases at year 2008
Fresh
Sed 10%
Landfill 4%
Est.
Sed 8%
Soils
43%
Ocean
23%
Landfill
56%
Ocean
32%
Landfill
15%
Ocean
35%
Horowitz et al., in prep

31. Atmospheric mass of Hg constraint from observations
Addition of commercial Hg to global biogeochemical model requires consideration of additional sinks
Atmospheric mass of Hg
Model with products
Mg of Hg
constraint from
observations
Model without products
We have a problem!!!!!!!!!!
Understanding tuned to just consider atmospheric emissions. Adding more sources – running into it w/ helen’s work too..
Retention in soils? More efficient transfer to armored and slow pools (relative to the respiration out etc)
Change can’t be coming from the atmosphere
Need more efficient transfer away from the active pools
Omg!!
Model was built/developed without inputs from products
Figure out a way to say that
-taking framework that didn’t have any knowledge of products
Need to adjust system – most uncertainty in terrestrial environment; Bess – mechanistic – her new cycling and put products in; we get more consistent picture
Work in progress!
Still refining budget etc
Uncertain fluxes; need to look into speciation etc;
range
We’re currently high – refining estimates; looking at categories with uncertainty – pesticides; paints;
We aren’t dismissing anyone’s work; continue to refine based on new science
Build on things; add new information – bess’s t
Show lower range
4600 – 5600 Mg!!
I would remove the dashed lines to simplify the plot. Make point that you increase atm loading by 50%, also change the trend over past few decades
I don't think that the second bullet is useful. It's a distraction. You can still make that point orally, that Corbitt is the latest version of the model and includes reduced...
Third bullet is ambiguous. You KNOW that the discrepancy can be resolved through refining of your substance flow analysis (like Hg2 speciation) and adjustment of ocean evasion.
We are missing a sink in the atmosphere – it will be something I need to address.
Need some hypotheses.
Incinerators emitted a lot of oxidized mercury: Streets: huge emission ratio of oxidized to elemental in incinerators!!
Rate of reduction; Hg deposition. Remove reduction – bring down atmospheric reservoir, would go in right direction but
Diurnal cycle of elemental mercury – dry deposition of elemental mercury could be increased.
Horowitz et al., in prep
lkj

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