Building a Global Modeling Capability for Mercury with GEOS-CHEM Noelle Eckley Selin EPS Day 12 March 2005

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) k=9.0(+/-1.3) x cm 3 s -1 (Pal & Ariya 2004) 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 Oxalate?

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? (Chris Holmes…) GEOS-CHEM simulation –Oxidation reactions: “best guess” from the published literature –Aqueous reduction: photochemically mediated, fixed reaction rate, proportional to [OH](g)

ATMOSPHERE Hg Hg(II) (trop.) 280 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

TGM: Model vs. Measurements + Continental sources in South America? Cruise data in the Pacific – inconsistent with Okinawa Underestimate of concentrations over the oceans

Comparing Model with Measurements: Hemispheric Average TGM Ratio of NH/SH in measurements: / (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

Data from Dan Jaffe

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

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

Wet Deposition: Model vs. Measurements High Hg deposition in tropical regions; Gradient with latitude Overestimate of deposition: Too much Hg(II)

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

Future Plans: “Mercury Depletion Events” (MDEs) in the Arctic Episodic depletion of TGM at polar sunrise Correlates with Arctic O 3 depletion events Mechanism: conversion to Hg(II) and subsequent deposition Proposed mechanism: reaction with BrO? AMAP, 2003

Changing Contaminant Pathways AMAP, 2003 Incoming solar radiation Precipitation (Rain/Snow) Ice Cover and gas exchange Air transport patterns

Collaborators/Acknowledgments Advisor: Prof. Daniel Jacob Rokjin Park Sarah Strode & Lyatt Univ. of Washington Chris Holmes Bob Yantosca

Anthropogenic Sources Source: Pacyna and Pacyna, 2002

Historical Record of Mercury from Ice Core Pre-industrial concentrations indicate natural source Episodic volcanic input Mining emerges Industrialization, and recent decrease Source: USGS

New vs. Old Mercury Source: Hintelmann et al. 2002