1. Global-scale Mercury Modeling: Status and Improvements Daniel J. Jacob with Noelle E. Selin 1, Christopher D. Holmes, Nicole V. Downey, Elizabeth D. Sturges and funding from NSF, EPA In collaboration with Lyatt Jaegle and Sarah Strode (U. Washington) Franz Slemr (MPI-Mainz) 1 now postdoc at MIT

2. FIRST Hg SIMULATION IN GEOS-Chem MODEL Selin et al. [JGR 2007] Ocean mixed layer coupled to atmosphere [Strode et al., GBC 2007] 33% from uptake by sea-salt aerosol TGM lifetime of 0.79 y

3. ANNUAL MEAN TGM CONCENTRATION IN SURFACE AIR Model (contours) and observations (circles) TGM simulation unbiased over land; can’t reproduce observations of high TGM from ships over NH oceans; but aircraft obsrervations over NE Pacific (R.W. Talbot, INTEX-B) don’t show high MBL values Selin et al. [JGR 2007]; Holmes et al., in prep Aircraft observations over NE Pacific, spring 2006 (R.W. Talbot)

4. TGM SEASONAL VARIATION AT NORTHERN MID-LATITUDES Observations Model oxn by OH only 12 sites oxn by O 3 only Hg(0) oxidation is clearly photochemical; Subsequent model implementation of seasonal variation of land emission [Selin et al., 2008] obviates need for photochemical Hg(II) reduction Selin et al. [JGR 2007]

5. INCREASE OF Hg(II) WITH ALTITUDE Global annual mean concentrations in GEOS-Chem Hg(0) Hg(II) Selin et al. [JGR 2007] reflects Hg(II) deposition sink, lack of Hg(II) reduction above boundary layer

6. SIMULATED vs. OBSERVED RGM AT Mt. BATCHELOR, OREGON (2.7 km) Model Observed: day (upslope) night (subsidence) all Evidence for high RGM in subsiding air masses High RGM events in observations reproduced only timidly by model; These events are anticorrelated with Hg(0), implying Hg(0)  Hg(II) conversion Swartzendruber et al. [2006]

7. CARIBIC Flights 2005-2007 Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container TGM Franz Slemr, MPI-C Aircraft sample upper troposphere/ lower stratosphere; measured TGM includes Hg(0) + some fraction of RGM

8. Hg(0) DEPLETION IN STRATOSPHERE TroposphereStratosphere lower stratosphereupper troposphere # observations749 (39%)1032 (52%) TGM (ng/m 3 ) 0.98 ± 0.30 1.32 ± 0.41 O 3 (ppb) 193 ± 135 58 ± 18 CO (ppb) 62 ± 20 92 ± 33 …but no indication of depletion events in troposphere Sturges et al. [in prep.]

9. TGM vs. ALTITUDE Pressure, hPa ng m -3 STP Sturges et al. [in prep.] Can we use the observed rate of decline as constraint on Hg(0) chemical loss?

10. GEOS-Chem vs. CARIBIC Fire plume upper troposphere lower stratosphere Observed events of rapid depletion in lower stratosphere – halogen chemistry? Sturges et al. [in prep.] 1:1 model sampled along flight tracks

11. MODEL vs. OBSERVATIONS AT OKINAWA Obs from Jaffe et al. [2005] Model Hg(0) correlated with CO in Asian outflow RGM not correlated with Hg(0) either in observations or model Diurnal cycle of RGM implies photochemical oxidant (Br rather than OH?), fast sink (simulated in model by uptake by sea-salt aerosol) Normalized mean diurnal cycle of RGM Selin et al. [JGR 2007]

12. RGM DIURNAL CYCLE IN MARINE BOUNDARY LAYER Holmes et al., in prep. U=4.4 m s -1 U=4.8 m s -1 U=7.7 m s -1 U=11.2 m s -1 model Data from Laurier et al. [2004], Jaffe et al. [2005], Laurier and Mason [2007] compared to box model for MBL with OH or Br as oxidants

13. BOX MODEL BUDGET FOR RGM IN MARINE BOUNDARY LAYER using Br and Cl as photochemical oxidants instead of OH Holmes et al., in prep.

14. GLOBAL OXIDATION OF Hg(0) BY ATOMIC Br Tropospheric Br y ubiquitous from oxidation of bromocarbons, release by sea salt Br (%) of Br y (March noon 180 °W) Global CTM simulation [Yang et al., 2005] (10 13 cm -2 ) Simulated BrO concentrations consistent with few remote sensing data available (0.1-1 pptv) Fractionation as Br is highest in upper toposphere (strong hv) HOBr BrNO 3 HBr hv, OH BrBrO O3O3 hv Br y yields global tropospheric lifetime for Hg(0)  Hg(II) of 0.5-1.7 years; Br could be a (the?) major Hg(0) oxidant! Holmes et al. [GRL 2006] Hg HgBrHgBrX X = OH, Br… Br T Goodsite et al. [2004] Donohoue et al. [2006]

15. Include land-atmosphere cycling for complete self-consistent cycling in land-atmosphere-ocean surface reservoirs Include Hg(0) deposition to land following Lin et al. [2006]; global mean V d = 0.03 cm s -1, exceeds 0.1 cm s -1 over vegetated land in daytime. This new sink Hg((1600 Mg a -1 ) requires a compensating increase in sources; we added biomass burning (600 Mg a -1 ), artisanal mining (450 Mg a -1 ), increased GEIA anthropogenic emissions in Asia by 50% [ Jaffe et al., 2005] (330 Mg a -1 ), increased GEIA by 30% in rest of world (300 Mg a -1 ) Model updates:

16. STEADY-STATE PREINDUSTRIAL (NATURAL) MERCURY CYCLE Key constraints: land and ocean in local steady state with atmosphere Pre-industrial deposition 1/3 of present (from soil cores) Pre-industrial soil reservoir 85% of present (from accumulated anthro emissions) Reservoirs in Mg Rates in Mg a -1 Selin et al. [GBC 2008]

17. Hg DEPOSITION FLUXES, PREINDUSTRIAL Selin et al. [GBC 2008] Use GEOS-Chem simulation of deposition fluxes to scale Hg soil concentrations driving land emission; iterate to steady state

18. STEADY-STATE SURFACE FLUXES OF MERCURY, PREINDUSTRIAL Selin et al. [GBC 2008] land deposition = soil volatilization + evapotranspiration + prompt recycling

19. GLOBAL MERCURY CYCLE: PRESENT-DAY vs. PRE-INDUSTRIAL Inventories in Mg Rates in Mg y -1 PRE-INDUSTRIAL PRESENT-DAY Selin et al. [GBC 2008]

20. ENRICHMENT FACTORS FOR PRESENT vs. PREINDUSTRIAL Hg DEPOSITION Selin et al. [GBC 2008]

21. SIMULATION OF U.S. MERCURY DEPOSITION NETWORK (MDN) DATA Seasonal variation vs. latitude Observations Model Model (N.Amer. sources) Annual mean wet deposition fluxes, 2004-2005: observations = circles, model = background Selin et al. [AE in press] Major contribution to mercury deposition from subsidence and scavenging of Hg(II) from global pool

22. SOURCE ATTRIBUTION FOR U.S. MERCURY DEPOSITION % contribution of N. American sources Natural (32%) North American anthropogenic (20%) Rest of world anthropogenic (31%) – half cycled through ocean on annual time scale Legacy anthropogenic re-emitted from soil on centurial time scale (16%) Selin et al. [AE in press] Hg(0) dry42% Hg(II) dry26% Hg(P) dry2% Hg(II) wet27% Hg(P) wet3% Deposition processes

23. NEXT GENERATION OF Hg GLOBAL LAND MODEL FOR GEOS-Chem: COUPLING TO ORGANIC CARBON Carbon dynamics simulated with the CASA biogeochemical model [Potter et al. 1992] Global 1x1 simulation Decomposition largely controlled by temperature Downey et al. [in prep.] will allow investigation of the effects of changing climate and land use Soil profile [Andersson, 1979]