1. Building a Global Modeling Capability for Mercury with GEOS-CHEM Noelle Eckley Selin GEOS-CHEM meeting 6 April 2005

2. 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 (1800-3600) (700-3500) (1680-3120) (1300-2600) (700-3500)

3. Hg 0 1.7 ng/m3 Gaseous Phase Aqueous Phase Hg 0 Henry’s Constant 0.11 M/atm Particulate Phase Oxidation Hg 2+ 10-200 pg/m3 Hg P 1-100 pg/m3 Hg 2+ k=8.7(+/-2.8) x 10 -14 cm 3 s -1 (Sommar et al. 2001) k=9.0(+/-1.3) x 10 -14 cm 3 s -1 (Pal & Ariya 2004) k=3(+/-2) x 10 -20 cm 3 s -1 (Hall 1995) Reported rate constants up to k=1.7 x 10 -18 cm 3 s -1 Henry’s Constant 1.4x10 6 M/atm OH O3O3 Oxidation HO 2 ? Reduction SO 3 k=1.1-1.7 x 10 4 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 Oxalate?

4. What does this mean for global modeling? Use observations from latitudinal gradient, seasonal cycles, and short-term variability to constrain uncertainties GEOS-CHEM simulation –Oxidation reactions: “best guess” from the published literature –Aqueous reduction: photochemically mediated, fixed reaction rate, proportional to [OH](g)

5. ATMOSPHERE Hg0 4260 Hg(II) (trop.) 280 Via OH:10236 Dry Deposition Ocean Emissions Land (Natural) Emissions Anthropogenic Emissions Land Re-emissions Hg(P) 2 775 204 Via O3: 2377 1500 1446 500 2000 Dry Deposition Wet Deposition 1041 5327 191 11 MERCURY BUDGET IN GEOS-CHEM Inventories in Mg Rates in Mg/yr k=8.7 x 10 -14 cm 3 s -1 k=3 x 10 -20 cm 3 s -1 τ = 0.77 yr τ = 7 days τ = 3.5 days Net ox: 5489 Reduction 7124

6. Emissions for GEOS-CHEM Hg Model CategoryAmount (Mg) Anthropogenic2200 Re-emission of previous anthropogenic from land1500 Land Primary Emissions500 Ocean2000

7. Model vs. Measurements + TGMRGM Continental sources in South America? Cruise data in the Pacific – inconsistent with Okinawa Underestimate of concentrations over the oceans Most measurements indicate low levels on average (5-20 pg/m3), with some spikes, diurnal variation Model has high average levels in some regions

8. Comparing Model with Measurements: Hemispheric Average TGM Ratio of NH/SH in measurements: 1.49 +/- 0.12 (Temme et al. 2003) Northern hemisphere average measurement ≈ 1.7 ng/m 3 Northern hemisphere average GEOS-CHEM: 1.62 ng/m 3 Ratio of NH/SH in GEOS-CHEM simulation: 1.5 –Shows that Hg lifetime in GEOS-CHEM is realistic Temme et al. 2003: black dots GEOS-CHEM: red line

11. Data from Dan Jaffe (Univ. of Washington) GEOS-CHEM captures the day-to-day variation in Hg0 at Okinawa. RGM is high by an order of magnitude. However, we do capture diurnal variation in RGM…without oxidation by halogens! RGM/10 at Okinawa vs. Measurements With ‘background’ subtracted off…

12. Banic et al. 2003: aircraft measurements of Hg0 over Ontario Vertical Profiles of Mercury GEOS-CHEM:Vertical profile over Ontario GEOS-CHEM: Latitudinal average Hg0

13. Hg(II) in the stratosphere? Supported by preliminary aircraft Measurements…

14. Future plans for GEOS-CHEM mercury simulation New land re-emission parameterization Examination of Arctic “Mercury Depletion Events” Changes in mercury transport pathways and budget under changing climate? Potential for application of inverse modeling?