Sarah Strode, Lyatt Jaeglé, Dan Jaffe, Peter Weiss-Penzias, Phil Swartzendruber University of Washington

Noelle Eckley Selin, Chris Holmes, Daniel Jacob Harvard

Trans-Pacific Transport of Mercury

Can GEOS-Chem capture observed Hg lrt events?

What can observed Hg/CO ratios tell us about Asian Hg emissions?

Hg emissions & long-range transport

Hg0 lifetime ~1 year global transport

Approx. 1/3 of emissions anthropogenic: ~50% from Asia underestimated?

Long-range transport important for North American concentrations

Pacyna et al., 2005 Seigneur et al.,

2004

Deposition to U.S.

Hg Emissions from Asia

SourcesMg/yr

Hg0 HgII HgP

Anthro 613 380 89

Natural 120 0 0

Reemis 373 0 0

BB 109 0 0

Land emission where geologic depositsLand reemissions follow deposition patternBiomass burning scaled to COEmissions+reemissions from slab ocean

Trans-Pacific Hg Transport

Hg0 & CO transported across PacificHgII at lower latitudes from Hg0 oxidation

March-May averages

Deposition largest over E. Asia & SW N. America

Asian anth CO at 700 hPa Asian anth Hg0 at 700 hPa

Asian anth HgII at 700 hPa Asian anth HgII deposition

Vertical View of Transport

March-May, 28°-60°N average

Asian Hg0 & CO trans-Pacific transport decreases w/ height

HgII transport in upper troposphere

Ocean reemission increases transport

Including ocean reemission of Asian Hg

Asia N. Am

Asian FF CO Asian anth Hg0 Asian anth HgII

Asian anth Hg0 Asian anth HgII

pres

sure

Timeseries at Okinawa, Spring 2004

Asian antrhopogenic tracer dominates variability

Asian land Hg tracer covaries with Asian anthro tracer

Obs from Jaffe et al. [2005]

CO obs and model

Hg0 obs and model

ALRTevent

Model

Asian anthro

Asian land

Constraining Asian Hg emissions

Observed Hg0/CO enhancement ratio during Asian LRT events ~twice ratio expected for emissions [Jaffe et al., 2005]:

Underestimate in anthropogenic Hg0 emission

Covariance w/ Asian land emission/reemission

Production of Hg0 during transport

Can the model distinguish these possibilities?

Slope= .0053, .0041, .0027

r2 = .84, .82, .84

Hg

0 (n

g/m

3 )

ng/m3/ppb Hg/CO

All Okinawa

Event mean

Obs 0.0053 0.0056

Std 0.0041 0.0050

Obs from Jaffe et al. [2005]

reduction of HgII emission adds ~20% increasing anth + decreasing land overestimates Hg0 conc.

RGM at MBO, April-Aug. 2005

Model captures timing of some events but underestimates magnitude

Greater subsidence could give higher RGM

Oxidation of global pool, not direct transport

Obs from Swartzendruber et al. [2006]

Conclusions & Future work

Land emissions + reduction of HgII can explain most of the observed Hg/CO ratio: anthropogenic inventory may be ok

Asian Hg0 reaches N. America by direct transport, while RGM descends from the high altitude global pool

Future plans: biogeochemical Hg cyclingMore sophisticated ocean formulationTrack Hg partitioning between soil, ocean, and atmospheric reservoirs thru time