Building a Global Modeling Capability for Mercury with GEOS-CHEM Noelle Eckley Selin, Rokjin J. Park, Daniel J. Jacob Constraining the global budget of mercury and atmospheric processes Providing boundary conditions for CMAQ Understanding the behavior of mercury in the Arctic Tracing pathways of intercontinental mercury pollution Evaluating the impact of climate change on mercury pathways

THE MERCURY CYCLE: CURRENT Wet & Dry Deposition 2600 ATMOSPHERE 5000 SURFACE SOILS 1,000,000 OCEAN 289,000 Net Wet & Dry Deposition 1900 Net Oceanic Evasion 1500 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 ( ) ( ) ( ) ( ) ( )

Hg ng/m3 Gaseous Phase Aqueous Phase Hg 0 Henry’s Constant 0.11 M/atm Particulate Phase Oxidation Hg pg/m3 Hg P pg/m3 Hg 2+ k=8.7(+/-2.8) x cm 3 s -1 (Sommar et al. 2001) One measured value in literature k=3(+/-2) x cm 3 s -1 (Hall 1995) Reported rate constants up to k=1.7 x cm 3 s -1 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

What does this mean for global modeling? Use observations from latitudinal gradient, seasonal cycles, and short-term variability to constrain uncertainties Potential for application of inverse modeling? GEOS-CHEM: 2 simulations –“Original” simulation: best guess from the published literature –“Improved” simulation: adjust oxidations to latitudinal gradient and observations

ATMOSPHERE: 4621 Hg Hg(II) 347 Via OH: 2769 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=1.98 x cm 3 s -1 k=3 x cm 3 s -1 τ = 0.82 yr τ = 21 days τ = 3.4 days

MeasuredImproved GEOS-CHEM Original GEOS-CHEM

Comparing Model with Measurements: Hemispheric Average TGM Ratio of NH/SH in measurements: / (Temme et al. 2003) Ratio of NH/SH in optimized GEOS-CHEM simulation: 1.49 –Shows that Hg lifetime in GEOS-CHEM is realistic Lamborg et al GEOS-CHEM

TGM: Model vs. Measurements Guiyang, China: Measured: 9.00 Modeled: Model is high at northern midlatitudes: overestimate of sources? Underestimate of sources In Asia?

Wet Deposition: Model vs. Measurements High Hg deposition in tropical regions; Gradient with latitude Overestimate of deposition: Reduction in sources needed (14%)?

Overestimate between 7-25% (depending on season): overestimate of sources?

Future plans for GEOS-CHEM Hg simulation Land and ocean re-emission parameterization: tracing emissions from source to receptor Source Region Chemistry and Deposition Land or Ocean Surface Reemission Receptor Region Emissions “tagged” by source and region Deposition “tagged” by source and region Source tag maintained through deposition and reemission process Ocean emissions model: collaboration with Sarah Strode, Lyatt Univ. of Washington

Old Mercury 920,000 preindustrial 80,000 postindustrial New Mercury Wet and Dry Deposition Historical Deposition Emissions “Old Mercury” soil concentrations initialized based on historical deposition patterns of natural, anthropogenic sources Quantities in Mg Re-emission Modeling in GEOS-CHEM Lifetime of “old mercury”: about 1000 yrs Lifetime of “new mercury: weeks to months