new perspectives on atmospheric mercury daniel j. jacob with noelle e. selin and christopher d....
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NEW PERSPECTIVES ON ATMOSPHERIC MERCURYNEW PERSPECTIVES ON ATMOSPHERIC MERCURY
Daniel J. Jacob
with Noelle E. Selin and Christopher D. Holmes
Supported by NSF, EPA
and Sarah Strode and Lyatt Jaegle (U. Washington)
RISING MERCURY IN THE BIOSPHERERISING MERCURY IN THE BIOSPHERE
3000-yr record in Swiss bog
Roos-Baraclough and Shotyk, ES&T 2003
Mercury in polar bear fur up 5-12X since 1890
Dietz et al., ES&T 2006
States with fish mercury advisories
GEOCHEMICAL CYCLE OF MERCURY (present)GEOCHEMICAL CYCLE OF MERCURY (present)
SOIL1000
ATMOSPHERE5.4
SURFACE OCEAN10
wet &dry deposition
evasion
rivers
0.5
SEDIMENTS
Natural (rocks, volcanoes)
Anthropogenic(fossil fuels)
evasion
0.2
burial
3.22.8
Inventories in Gg, fluxes in Gg yr-1
2.2 1.5
DEEP OCEAN280
LAND SURFACE
uplift
3.8
2.3
0.6
0.5
Selin et al. [2006],Strode et al. [2006]
SOURCE-DEPOSITION RELATIONSHIPS OF MERCURYSOURCE-DEPOSITION RELATIONSHIPS OF MERCURYCONTROLLED BY ATMOSPHERIC CHEMISTRYCONTROLLED BY ATMOSPHERIC CHEMISTRY
Hg(0) Hg(II)
SURFACE RESERVOIRS(LAND, OCEAN)
ATMOSPHERE
Hg(II)Hg(0)hv, bio
OH (80%), O3 (20%), Br,…?
aqueous hv?
combustion
H ~ 106 M atm-1
fast depositionH = 0.1 M atm-1
3.9 0.3
148
dry
4.7wet
2.1
4.8
1.3 0.7
Tropospheric nventories in Gg, fluxes in Gg yr-1
evasion
Selin et al. [2006],
ANTHROPOGENIC EMISSIONS OF MERCURY:ANTHROPOGENIC EMISSIONS OF MERCURY:recent shift from N.America/Europe to Asiarecent shift from N.America/Europe to Asia
Africa 407 (18%)
South America92 (4%)
North America202 (9%)
Europe239 (11%)
Australia 125 (6%)
Asia1204 (52%)
Europe627 (33%)
Asia705
(38%)
Africa 178 (9%)
Australia 48 (3%)
North America261 (14%)
South America62 (3%)
1990Total: 1.88 Gg yr-1
2000Total: 2.27 Gg yr-1
Pacyna and Pacyna, 2005
GEOS-Chem GLOBAL 3-D SIMULATION GEOS-Chem GLOBAL 3-D SIMULATION OF ATMOSPHERIC AND OCEANIC MERCURYOF ATMOSPHERIC AND OCEANIC MERCURY
• Atmospheric chemical transport model (CTM) driven by assimilated meteorological data from the NASA Global Modeling and Assimilation Office (GMAO) with 3-6 h frequency, 1ox1o horizontal resolution
• Mercury simulation includes • dynamic coupling of atmosphere and slab mixed layer ocean• Hg(0), Hg(II), and inert particulate Hg in both atmosphere and ocean• emissions, chemistry, deposition as described in previous slides• horizontal resolution 4ox5o
SIMULATION OF TOTAL GASEOUS MERCURY (TGM)SIMULATION OF TOTAL GASEOUS MERCURY (TGM)
Land-based sitesobserved: 1.58 ± 0.19 ng m-3
model: 1.60 ± 0.10 ng m-3
…but not clear why NH cruise data are so high!
Annual mean surface air concentrations and ship cruise data
Selin et al., 2006
Circles are observations; background is model
R2=0.51
SEASONAL VARIATION OF TGM AT NORTHERN MID-LATITUDESSEASONAL VARIATION OF TGM AT NORTHERN MID-LATITUDES
12 sites
ObservedModel (standard)Model (OH oxidation only)Model (O3 oxidation only)
Selin et al., 2006
some evidence for photochemical redox chemistry of Hg
Hg DEPOSITION OVER U.S. : LOCAL VS. GLOBAL SOURCESHg DEPOSITION OVER U.S. : LOCAL VS. GLOBAL SOURCES
Wet deposition fluxes, 2003-2004 (background=model,dots=measured)
max in southeast U.S. from oxidation of global Hg pool
2nd max in midwest from regional sources (mostly dry deposition in GEOS-Chem)
2/3 of Hg deposition over U.S. in model is dry, not wet!
Simulated % contribution of North American sources to total Hg deposition U.S. mean: 20%
Selin et al. [2006]
OBSERVATIONS AT OBSERVATIONS AT OKINAWA (Asian outflow)OKINAWA (Asian outflow) Observed (Jaffe et al., 2005)
Model
CO
Hg(0)
RGM
Reactive gaseous mercury (RGM)is gas-phase component of Hg(II)
• Correlation of Hg(0) with CO (r2 = 0.84 in obs, 0.91 in model) indicates dominant Asian source(underestimated by 30% in model)
• RGM not correlated with Hg(0) either in model or observations;source from subsidence
DIURNAL CYCLE OF RGM AT OKINAWA DIURNAL CYCLE OF RGM AT OKINAWA
ObservationsModel
Large diurnal cycle at Okinawa implies• a photochemical source (OH in the model – but Br would better explain early-morning rise)• a very fast sink (uptake by sea salt aerosols in the model)
Selin et al. [2006]
von Glasow et al., GRL 2002
OH
Br
Pro
duct
ion
Rat
e
Typical diurnal variation of OH and Br
PREDICTION OF INCREASING Hg(II) WITH ALTITUDE PREDICTION OF INCREASING Hg(II) WITH ALTITUDE
Hg(II) Hg(0)
because Hg(II) loss is largely restricted to lower troposphere: dry deposition, precipitation, clouds
Selin et al. [2006]
SIMULATED vs. OBSERVED RGMSIMULATED vs. OBSERVED RGMAT Mt. BATCHELOR, OREGON AT Mt. BATCHELOR, OREGON
(2.7 km)(2.7 km)
ModelObserved: 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), reflecting Hg(0) Hg(II) conversion
Swartzendruber et al. [2006]
FAST Hg OXIDATION BY Br OBSERVED IN POLAR SPRINGFAST Hg OXIDATION BY Br OBSERVED IN POLAR SPRING
Hg HgBr HgBrXX = OH, Br…Br
T
Tropospheric BrO Sep 1997
GOME - SLIMCAT
Hg(0) depletion events observed togetherwith ozone depletion events
Spitzbergen data [Sprovieri et al., 2005] Theys et al. [2004]
High tropospheric BrO inpolar spring
O3
Hg(0)
ATOMIC Br UBIQUITOUS IN TROPOSPHEREATOMIC Br UBIQUITOUS IN TROPOSPHEREfrom oxidation of bromocarbons, release by sea salt
Br (%) of Bry (March noon 180°W)
Global CTM simulation [Yang et al., 2005](1013 cm-2)
Simulated BrO concentrations consistent with few remote sensing data available (0.1-1 pptv)
Fractionation as Br is highest inupper toposphere (strong hv)
HOBrBrNO3
HBr
hv, OH
Br BrOO3
hv
Bry
GLOBAL OXIDATION OF Hg(0) BY ATOMIC BrGLOBAL OXIDATION OF Hg(0) BY ATOMIC Br
Br concentrations [Yang et al., 2005] resulting Hg(0) lifetime
yields global tropospheric lifetime for Hg(0) Hg(II) of 200 days (160-510); Br could be a (the?) major Hg(0) oxidant!
Holmes et al. [2006]
SOME INDIRECT EVIDENCE FOR Hg OXIDATION BY BrSOME INDIRECT EVIDENCE FOR Hg OXIDATION BY Br
RGM
O3
TGM
RGM
O3
TGM
Mercury depletion event in Antarctic summerassociated with elevated ozone [Temme et al., 2003]: subsidence of upper tropospheric air?
Single-particle aircraft observations [Murphy et al., 2006]; elevated aerosol Hg(II) above tropopause associated with elevated Br
EFFECTS OF CLIMATE CHANGE ON MERCURY CYCLEEFFECTS OF CLIMATE CHANGE ON MERCURY CYCLE
Precipitation
Winds
Exchange withSurface reservoirs
Ocean currents
biota
Chemistry