Challenges in Global Mercury Modeling Ashu Dastoor Meteorological Service of Canada Environment Canada Acknowledgements: Didier Davignon and Arturo Quintanar

Atmospheric Mercury Cycling Gas-phase chemistry GEM ↔ RGM ↔ TPM O3, OH, H2O2, Halogens: tropospheric chemistry Q: reactions, rates and products? Heterogeneous Chemistry ? Aerosol dynamics Q: TPM size distribution? Planetary Boundary Layer Turbulent mixing met model Anthropogenic emissions GEM, RGM, TPM Q: emission speciation and plume chemistry? Flue gas chemistry? Point sources Plume rise Volcanic emissions Q: inventory? Bio-mass burning emissions Q: inventory? Surface natural and re-emission: soils, vegetation water bodies, snow, oceans Q: inventory/processes? Wet deposition Met model Q: precipitation scavenging? Evaporation Met model Gas/liquid exchange Transport Met model Transport Dry deposition Q: deposition velocities? Cloud properties Met models Snow/Ice dynamics Ice model Evaporation Area emissions Mercury transformation processes Q: residence time and revolatilization rate and species? GEM↔RGM↔TPM O 3, OH, HO 2, (Cl), SO 3, aerosols: tropospheric chemistry Q: reactions, rates and products?

Goals for a Global Mercury Model towards estimating Mercury in Lake Ontario What is the atmospheric flux of Hg that arrives to Lake Ontario from global anthropogenic sources? What is the atmospheric flux of Hg that arrives to lake Ontario from global natural and recycled sources? What are the sources of this distant mercury? What is the speciation of transported mercury? What is the time-space distribution of this flux? How are the fluxes changing with changing emissions? What is the contribution of distant mercury to the deposition in Lake Ontario basin? This question can be better answered by a regional model using the atmospheric background and boundary flux information from global models. Preliminary results from N. American model intercomparison study indicate significant impact of trans-boundary flows of mercury to the regional deposition. The study compares impact of boundary fluxes from three different global models.

Major Challenges faced by a global model in addressing the goals Emissions: Natural and re-emissions from land and ocean surfaces (very few flux measurements and no emissions inventory) Mercury Chemistry: Chemical reactions- products, rates and phase Mercury dry deposition process What is the trend in natural and re- emissions of mercury relative to the anthropogenic emissions?

THE MERCURY CYCLE: CURRENT Wet & Dry Deposition 3500 ATMOSPHERE 5000 SURFACE SOILS 1,000,000 OCEAN 288,000 Wet & Dry Deposition 3100 Oceanic Evasion 2600 Net burial 200 Land emissions 1600 Quantities in Mg/year Uncertainty ranges in parentheses Adapted from Mason & Sheu, 2002 Anthropogenic Emissions 2400 Extraction from deep reservoirs 2400 River 200 ( ) ( ) ( )

Ocean flux distribution kg July ocean flux Jan. ocean flux latitude Jan. July Higher flux in tropics due to high temperature and radiation High flux in regions of high deposition Seasonality, spatial variation due to temperature, npp, radiation, and mixed layer depth Diurnal variation: photochemistry

Hg ng/m3 Gaseous Phase Aqueous Phase Hg 0 Henry’s Constant 0.11 M/atm Particulate Phase Oxidation Hg 2+ Products and phase unclear pg/m3 Hg P pg/m3 Hg 2+ k=8.7(+/-2.8) x cm 3 s -1 (Sommar et al. 2001) k=9.3(+/-1.3) x cm 3 s -1 (Pal & Ariya 2004) Probably unimportant reaction (Goodsite et al. 2004) k=3(+/-2) x cm 3 s -1 (Hall 1995) k=7.5(+/-0.9) x cm 3 s -1 (Pal and Ariya 2004) Longer lifetime suggested (Calvert & Lindberg 05) Henry’s Constant 1.4x10 6 M/atm OH O3O3 Oxidation HO 2 ? Reduction SO 3 k= x 10 4 M -1 s -1 (Pehkonen & Lin 1998) Shouldn’t occur (Gårdfeldt & Jonsson 2003) k= (+/ ) s -1 (vanLoon et al. 2000) Occurs only where high sulfur, low chlorine Oxalate?

Is there Hope? Global model is a closed atmospheric system therefore observations can be used to constrain uncertainties. Observations available: atmospheric mercury concentrations, wet deposition, terrestrial and aquatic fluxes of mercury and measurements of long-range transport of mercury.

ATMOSPHERE Hg0 Hg(II) Via OH:10236 Dry Deposition Ocean Emissions Land (Natural) Emissions Anthropogenic Emissions Land Re-emissions Hg(P) Via O3: Dry Deposition Wet Deposition MERCURY BUDGET IN GEOS-CHEM Inventories in Mg Rates in Mg/yr k=8.7 x cm 3 s -1 k=3 x cm 3 s -1 τ = 0.77 yr τ = 7 days τ = 3.5 days Net ox: 5489 Reduction 7124

How are we addressing the goals? Develop a well constrained global model with known chemistry and emissions. Use the constrained model to address the goals. Perturb the system using emerging chemical mechanism for mercury on the global balance of mercury and provide possible solutions. Assess the impact of emerging mercury chemistry on long range transport of mercury and trans-boundary fluxes of mercury for regional models. Evaluate the accuracy of trend in anthropogenic emissions inventory by modeling the global budgets and verify the changes against the observations. Develop detailed processes such as mercury evasion from snow, soil, vegetation etc and including aerosol dynamics.

90S 60S 30S Eq. 30N 60N 90N Latitude Observed (left; Lamborg et al., 2002) and modeled (right) Inter-hemispheric gradient of TGM Observed and from GRAHM simulation

Elemental mercury vapor concentration at Alert for the whole year 1995

Rapid, near-complete depletion of mercury observed during spring in the Arctic, sub-Arctic and Antarctic is which is also correlated with ozone depletion. Questions: Which halogen gases are responsible and what is the impact on the Arctic and global mercury deposition? Mercury deposition without MDEsMercury deposition with MDEs Main conclusions: Br atoms (~.4 day) and BrO (~1 day) radicals are the most effective halogens driving mercury oxidation to more hygroscopic species which are readily deposited and could be incorporated in the biota. MDEs in the Arctic increase the net deposition into the Arctic by 100 tons/yr. Net accumulation in the Arctic 325 tons/yr The Arctic: a sink for mercury

Slow oxidation of Hg 0 by O 3 in the troposphere – 1-2 years life time Fast oxidation of Hg0 by halogens in the polar regions and marine boundary layer – hours - 10 days life time Hg 0 Hg II Surface ocean Evasion deposition transport reduction Hg 0 Hg II Marine Boundary Layer Fast oxidation Loss Reduction proportional to radiation and net primary productivity transport Sea-salt aerosol Halogen activation Cl2, Br2, Cl, Br, BrO

Impact of mbl chemistry on transboundary flow from Asia Surface air mercury concentrations(ng/m3) MBL chemistry No MBL chemistry

Impact of mbl chemistry on total mercury deposition (ug/m3) MBL Chemistry No MBL Chemistry

Canada USA Arctic Surface air Hgo concentrationsTotal deposition in ug/m2/year No MBL MBL

Spring 2004 Experiment: Simultaneous Observations at Mt.Bachelor and Okinawa ( Jaffe et al. 2005) MBO Okinawa Okinawa: Hg 0,RGM, PHg, CO, O 3, aerosols, etc. MBO: Total Hg 0, CO, O 3, aerosols, etc. Mauna Loa

Jaffe et al. 2005

Vector winds 700 mb, April mean

Hg transport to North America: April 25 th, 2004 ΔHg/ΔCO=0.50 ng/m3/100 ppbv Good tracer of Asian air masses Suggests much larger Asian emissions? (Jaffe et al. 2005)

Possible causes for this discrepancy: Underestimate of the industrial or domestic Hg emissions; Natural emissions; Re-emission of previously deposited Hg; Too low a ratio of Hg 0 /total Hg in the inventory; Conversion of RGM to Hg 0 during transport; Explanations/Hypotheses (Jaffe et al. 2005)  Using the observed Hg 0 /CO ratio, and the known CO emissions, Jaffe et al. calculate Hg 0 emissions from Asia of 1460 mt/year (+/-30%);  This can be compared to 770 mt/year in the Pacyna et al., 2003 inventory.

Anthropogenic Air Emissions of Mercury: Distribution by Region in 1990 and 2000 Total: 1,881 metric tons/yrTotal: 2,269 metric tons/yr Asia and Africa account for about 70% of global emissions and show steady, significant increases due to industrialization. Based on Pacyna, J., Munthe J., Presentation at Workshop on Mercury: Brussels, March 29-30, 2004 Slide courtesy Grace Howland, Air Pollution Prevention Directorate, Environment Canada Africa 9% Asia 38% Australia 3% Europe 33% North America 14% South America 3% Africa 18% Asia 52% Australia 6% Europe 11% North America 9% South America 4%

GRAHM simulation with year 2000 Global mercury emissions January GEM ng/m3 July GEM ng/m3

JanuaryJuly GEM surface air concentrations ng/m**3 GRAHM simulation with year 1990 global emissions

Impact of mercury emission reductions Impact of proposed Canada wide standards for coal-fired power plants- Reduction of 1,224 kg/yr will result in ~ 580 kg/yr reduction in total mercury deposition over Canada Impact of proposed US mercury rule for coal-fired power plants- Reduction of 30,000 kg/yr will result in ~ 2,600 kg/yr reduction in total mercury deposition over Canada Asia contributes ~ 24,700 (21,650 with mbl chemistry) kg/yr mercury deposition into Canada of which ~ 15,300 kg/yr comes from China.