Building a Global Modeling Capability for Mercury with GEOS-CHEM

1. Building a Global Modeling Capability for Mercury with GEOS-CHEM • 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 Noelle Eckley Selin, Rokjin J. Park, Daniel J. Jacob

2. THE MERCURY CYCLE: CURRENT ATMOSPHERE 5000 Anthropogenic Emissions 2400 Wet & Dry Deposition 2600 Land emissions 1600 Net Wet & Dry Deposition 1900 Net Oceanic Evasion 1500 (1680-3120) (1300-5400) (320-8000) (950-3800) (300-7500) SURFACE SOILS 1,000,000 OCEAN 289,000 River 200 Extraction from deep reservoirs 2400 (1680-3120) Quantities in Mg/year Uncertainty ranges in parentheses Adapted from Mason & Sheu, 2002 Net burial 200

3. k=8.7(+/-2.8) x 10-14 cm3 s-1 (Sommar et al. 2001) One measured value in literature OH Hg0 1.7 ng/m3 Gaseous Phase Hg2+ 10-200 pg/m3 Oxidation O3 k=3(+/-2) x 10-20 cm3 s-1 (Hall 1995) Reported rate constants up to k=1.7 x 10-18cm3 s-1 Henry’s Constant 0.11 M/atm Henry’s Constant 1.4x106 M/atm Oxidation Hg0 Aqueous Phase ? Hg2+ SO3 HO2 Reduction • k=1.1-1.7 x 104 M-1 s-1 (Pehkonen & Lin 1998) • Shouldn’t occur (Gårdfeldt & Jonsson 2003) • k=0.0106 (+/- 0.0009) s-1 (vanLoon et al. 2000) • Occurs only where high sulfur, low chlorine Particulate Phase HgP 1-100 pg/m3

4. 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

5. MERCURY BUDGET IN GEOS-CHEM ATMOSPHERE: 4621 τ = 0.82 yr τ = 3.4 days τ = 21 days Hg0 4272 Hg(P) 2 Hg(II) 347 Via OH: 2769 k=1.98 x 10-14 cm3 s-1 Via O3: 2444 k=3 x 10-20 cm3 s-1 2000 1500 775 1446 204 Land Re-emissions Ocean Emissions 2227 160 Anthropogenic Emissions 500 Dry Deposition 43 3673 Wet Deposition Land (Natural) Emissions Wet Deposition Inventories in Mg Rates in Mg/yr Dry Deposition

6. Original GEOS-CHEM Measured Improved GEOS-CHEM

7. Comparing Model with Measurements: Hemispheric Average TGM • Ratio of NH/SH in measurements: 1.49 +/- 0.12 (Temme et al. 2003) • Ratio of NH/SH in optimized GEOS-CHEM simulation: 1.49 • Shows that Hg lifetime in GEOS-CHEM is realistic GEOS-CHEM Lamborg et al. 2002

8. TGM: Model vs. Measurements Guiyang, China: Measured: 9.00 Modeled: 2.98 Underestimate of sources In Asia? + Model is high at northern midlatitudes: overestimate of sources?

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

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

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

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