|
Read Full Article (file size: 780104 bytes) Cited by
JOURNAL OF GEOPHYSICAL RESEARCH,
VOL. 112,
D02308,
doi:10.1029/2006JD007450,
2007
Chemical cycling and deposition of atmospheric mercury: Global constraints from observations
Noelle E. Selin
Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA
Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA
Daniel J. Jacob
Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA
Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA
Rokjin J. Park
Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA
Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA
Robert M. Yantosca
Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts, USA
Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA
Sarah Strode
Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA
Lyatt Jaeglé
Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA
Daniel Jaffe
Interdisciplinary Arts and Sciences, University of Washington, Bothell, Washington, USA
Abstract
We use a global 3-D model of atmospheric mercury (GEOS-Chem) to interpret worldwide observations of total gaseous mercury
(TGM) and reactive gaseous mercury (RGM) in terms of the constraints they provide on the chemical cycling and deposition of
mercury. Our simulation including a global mercury source of 7000 Mg yr−1 and a TGM lifetime of 0.8 years reproduces the magnitude and large-scale variability of TGM observations at land sites. However,
it cannot capture observations of high TGM from ship cruises, implying a problem either in the measurements or in our fundamental
understanding of mercury sources. Observed TGM seasonal variation at northern midlatitudes is consistent with a photochemical
oxidation for Hg(0) partly balanced by photochemical reduction of Hg(II). Observations of increasing RGM with altitude imply
a long lifetime of Hg(II) in the free troposphere. We find in the model that Hg(II) dominates over Hg(0) in the upper troposphere
and stratosphere and that subsidence is the principal source of Hg(II) at remote surface sites. RGM observations at Okinawa
Island (Japan) show large diurnal variability implying fast deposition, which we propose is due to RGM uptake by sea-salt
aerosols. Observed mercury wet deposition fluxes in the United States show a maximum in the southeast, which we attribute
to photochemical oxidation of the global Hg(0) pool. They also show a secondary maximum in the industrial Midwest due to regional
emissions that is underestimated in the model, possibly because of excessive dry deposition relative to wet (dry deposition
accounts for 68% of total mercury deposition in the United States in the model, but this is sensitive to the assumed phase
of Hg(II)). We estimate that North American anthropogenic emissions contribute on average 20% to U.S. mercury deposition.
Received 27
April
2006;
accepted 9
August
2006;
published 30
January
2007.
Keywords: mercury;
GEOS-Chem;
oxidation;
reduction;
deposition.
Index Terms: 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0345 Atmospheric Composition and Structure: Pollution: urban and regional (0305, 0478, 4251); 0368 Atmospheric Composition and Structure: Troposphere: constituent transport and chemistry.
Read Full Article (file size: 780104 bytes) Cited by
Citation: Selin, N. E., D. J. Jacob, R. J. Park, R. M. Yantosca, S. Strode, L. Jaeglé, and D. Jaffe
(2007),
Chemical cycling and deposition of atmospheric mercury: Global constraints from observations,
J. Geophys. Res.,
112,
D02308,
doi:10.1029/2006JD007450.
Copyright 2007 by the American Geophysical Union.
|