CONSTRAINTS FROM RGM MEASUREMENTS ON GLOBAL MERCURY CHEMISTRY

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CONSTRAINTS FROM RGM MEASUREMENTS ON GLOBAL
MERCURY CHEMISTRY

• Noelle Eckley Selin1
• Daniel J. Jacob1, Rokjin J. Park1, Robert M.
  Yantosca1, Sarah Strode, Lyatt Jaegle, Daniel
  Jaffe

1Harvard University Department of Earth and
Planetary Sciences Atmospheric Chemistry Modeling
Group
Mercury 2006 Madison, WI, USA 10 August 2006
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MERCURY IN THE ATMOSPHERE
REACTIVE GASEOUS MERCURY (RGM)
TOTAL GASEOUS MERCURY (TGM)
GAS PHASE
AQUEOUS PHASE
Hg(II)
Oxidation OH, O3, Br(?)
Hg(0)
SOLID PHASE
VERY SOLUBLE
RELATIVELY INSOLUBLE ATMOSPHERIC LIFETIME
ABOUT 1 YEAR TYPICAL LEVELS 1.7 ng m-3
Reduction Photochemical aqueous (?)
Hg(II)
Hg(P)
LIFETIME DAYS TO WEEKS TYPICAL LEVELS
1-100 pg m-3
DRY AND WET DEPOSITION
ECOSYSTEM INPUTS
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MERCURY BUDGET IN GEOS-Chem
Hg(0) 4500 (3900)
Hg(II) 860 (300)
OH12000
Hg(P) 1.9 (1.9)
O32400
hv (cloud)8300
200
700
1300
1500
500
2800
Anthropogenic emission
4700
Land re-emission
190
10
2100
Ocean emission
Land (primary) emission
Dry deposition
Wet deposition
Inventories in Mg (Troposphere in
parentheses) Rates in Mg/yr
Wet deposition
Dry deposition
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CONSTRAINTS FROM ANNUAL MEAN MEASUREMENTS
TGM Average concentration at 22 land-based sites
Measured 1.58 0.19 ng/m3 Simulated 1.63
0.10 ng/m3 High Atlantic cruise data?
Hg(II)Hg(P) Average simulated concentrations
over continents 17-47 pg/m3 Consistent with
measurements High values over poles where
reduction suppressed Low values over oceans
fast sink due to uptake by sea salt

Selin et al. 2006, JGR
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CONSTRAINTS FROM TIME SERIES AT OKINAWA
Observed (Jaffe et al., 2005) Model
CO correlated with Hg(0), but not with
RGM Implies Asian source (underestimated by 30
in the model) Model captures day-to-day
variations in CO, Hg(0), RGM RGM diurnal
variation (next slide) Day-to-day variation of
RGM driven by suppression of dry deposition
Selin et al. 2006, JGR
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OKINAWA CONTINUED SEA-SALT SINK?

• Previous GEOS-Chem vs. measurements at Okinawa
  by Jaffe et al. (2005) model overestimates
  measurements by a factor of 3 (note difference in
  scale), but captures some day-to-day variation in
  observations

• Revised Model and measured RGM including an
  implied sink for RGM (sea salt uptake?) are
  consistent with order of magnitude of Okinawa
  observations (same scale)

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DIURNAL CYCLE OF RGM AT OKINAWA
Observations Model
Typical diurnal variation of OH and Br

• Diurnal cycle of RGM at Okinawa
• morning increase (photochemical production)
• fast sink (propose uptake onto sea-salt aerosol)

Selin et al. 2006, JGR
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A HIGH-ALTITUDE RGM SOURCE?
Hg(II) Hg(0)
Observations Model
Measurements of RGM at Mt. Bachelor, Oregon (2.7
km) show elevated levels relative to surface
measurements mean 43 pg m-3 Swartzendruber et
al. 2006, JGR, submitted
Vertical distribution of Hg(0) mixing ratios near
southern Japan. Observations from the ACE-Asia
aircraft campaign in April-May 2001 Friedli et
al., 2004
Selin et al. 2006, JGR
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CONSTRAINTS FROM TIME SERIES AT MT. BACHELOR,
OREGON
Vertical profile of GEOS-Chem vs. measurements at
Mt. Bachelor ?daytime ? (blue)all ? nighttime
Measurements of RGM at Mt. Bachelor, Oregon (2.7
km) show elevated levels relative to surface
measurements mean 43 pg m-3 Model does not
capture episodes of very high RGM
Swartzendruber et al. 2006, JGR, submitted
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DEPOSITION LOCAL VS. GLOBAL SOURCES

• Two patterns of mercury wet deposition over the
  U.S.
• (backgroundmodel, dotsmeasured)
• Latitudinal gradient (higher in warm, sunny, wet
  places, e.g. Florida, Texas). From oxidation of
  global pool of Hg(0) and subsequent rainout
• Near-source wet deposition of locally-emitted
  Hg(II) and Hg(P) (underestimated in GEOS-Chem)

contribution of North American sources to total
(wet dry) deposition GEOS-Chem model U.S.
mean 20 Reflects influence of
locally-deposited Hg(II) and Hg(P) in source
regions
Measurements Mercury Deposition Network, 2006
GEOS-Chem Selin et al. 2006
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Acknowledgments

• This work was funded by the Atmospheric Chemistry
  Program of the U.S. National Science Foundation,
  by a U.S. Environmental Protection Agency (EPA)
  Science to Achieve Results (STAR) Graduate
  Fellowship to NES, and by the EPA
  Intercontinental Transport of Air Pollutants
  (ICAP) program.