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 Tracing pathways of mercury pollution to the Arctic Understanding the behavior of mercury in the Arctic Evaluating the impact of climate change on mercury pathways ACIA International Scientific Symposium on Climate Change in the Arctic Reykjavik, Iceland, 10 November 2004

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? GEOS-CHEM: 2 simulations –“Original” simulation: best guess from the published literature –“Improved” simulation: adjust oxidations to latitudinal gradient and observations In progress: simulation taking into account aqueous reduction reactions

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 = 5 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%)?

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

Global Change and Air Pollution (GCAP) Project L GISS GCM, with changing GHGs Spin-up of ocean GEOS-CHEM Calculate global chemistry archived temperatures, humidity, winds, etc Loretta J. Mickley, Shiliang Wu, and Daniel J. Jacob (Harvard Univ.), et al. Application to Mercury Simulation (N.E. Selin) Air quality applications Regional modeling Emissions scenarios