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