AN ATMOSPHERIC CHEMIST’S VIEW OF THE WORLD

                                                                                                                                                                                       

Fires Landbiosphere

Humanactivity

        

Lightning

iiii LPntn

)( U

Ocean physicschemistrybiology

“SHORT-LIVED CLIMATICALLY RELEVANT COMPOUNDS”the role of air-sea exchange

• Recognized priorities: sulfur and halogen chemistry– What controls DMS emission to the atmosphere?– What reactions control sulfate production in the MBL?– What controls the nucleation of sulfate aerosol?– What are the abundances and sources of halogen radicals in the

MBL?

• Two new directions: – Atmospheric budgets of O- and N-containing organics

(carbonyls, alcohols, cyanides,…)– Oceanic tracers of marine convection in meterorological models

ATMOSPHERIC ACETONE (0.2-3 ppbv): major source of HOx radicals in upper troposphere,

agent for conversion of NOx to PAN

Aircraft observations over the NW Pacific [Singh et al., 1995]

Atmospheric observations of acetone

TRACE-A

SONEX

ABLE-3B PEM

-WB

PEM-TB

Surface sites

GLOBAL BUDGET OF ATMOSPHERIC ACETONE [Singh et al., 2000]

SOURCES (Tg yr-1): 56 (37-80) – Atm oxidation of propane, other iso-HCs 17 (12-24)– Terrestrial vegetation 15 (10-20)– Atm oxidation of terpenes, methylbutenol 11 (7-15)– Plant decay 6 (4-8)– Biomass burning 5 (3-10)– Industry 2 (1-3)– Terrestrial vegetation 33 +/- 9

SINKS (Tg yr-1): 56 (37-80)– Photolysis 36 (24-51)– Oxidation by OH 13 (9-19)– Dry deposition 7 (4-10)

ATMOSPHERIC LIFETIME: 16 days

OCEANIC SIGNATURE IN ATMOSPHERIC ACETONE OBSERVATIONS?

Low winter valuesover Europe:ocean sink?

southern Sweden[Solberg et al., 1996]

High values overSouth Pacific:ocean source?

South Pacific[Singh et al., 2001]

ROLE OF OCEANIN ATMOSPHERIC BUDGET OF ACETONE

Biological uptake(Kieber et al., 1990)

SINK?

H298 = 30 M atm-1;physical uptake limitedby both gas- and aqueous-phase transfer

h

organic microlayer

SOURCE?

Zhou andMopper (1997)

measurements of oceanic acetone are very few!

Observed atmosphericconcentrations (with “errors”)

Global 3-D model (“forward model”):defines sensitivity of atmospheric concentrations

to global sources/sinks (“state vector”)

INVERSE MODEL ANALYSIS OF ACETONE BUDGET

Optimized estimateof sources/sinks

A priori best estimateof sources/sinks

(with errors)

GLOBAL 3-D MODEL SIMULATION OF ATMOSPHERIC ACETONE

a priori sources/sinksOptimized sources/sinks(including “microbial” ocean sink,photochemical ocean source)

OPTIMIZED BUDGET OF ATMOSPHERIC ACETONE

SOURCES (Tg yr-1): 95 +/- 15– Ocean (photochemical) 27 +/- 6

– Atm oxidation of propane, other iso-HCs 21 +/- 5– Atm oxidation of terpenes, methylbutenol 7 +/- 4– Biomass burning 5 +/- 2– Plant decay 2 +/- 5– Industry 1 +/- 1

SINKS (Tg yr-1): 95 – Photolysis 46– Oxidation by OH 27– Ocean uptake 14– Dry deposition to land 9

ATMOSPHERIC LIFETIME: 15 days

HENRY’S LAW ALONE WOULD IMPLY A LARGE OCEAN EFFECT ON THE ATMOSPHERIC BUDGETSOF A RANGE OF MODERATELY SOLUBLE GASES

Species Atm lifetime H Atm lifetime mOceanML/mAtm

(chemical loss) (M atm-1) (ocean uptake) ( Henry’s law, dimensionless)

Acetone 20 days 70 17 days 10

Methanol 17 days 500 11 days 80

HCN 2.5 years 30 20 days 5

Assuming ocean T = 283K, ML depth = 50m, surface wind U = 5 m s-1

T-dependent!

ATMOSPHERIC COLUMN OBSERVATIONS OF HCNSHOW VARIABILITY CONSISTENT WITH OCEAN SINK

Lines: global 3D model with biomass burning source,ocean uptake [Li et al., 2000]

Symbols:Observations[Zhao et al., 2000]

Implied ocean uptake of 1-3 Tg N yr-1 would makesignificant contribution to N deposition to open ocean

TIP OF THE ICEBERG?LARGE MARINE SOURCE OFACETALDEHYDE

PEM-TB South Pacific observations [Singh et al., 2001]

Model withoutmarine source

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ALTI

TUD

E, k

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PAN, ppt

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FORMALDEHYDE, ppt

(b)

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ALTI

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ACETALDEHYDE, ppt

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ACETONE, ppt

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PAN

HCHO

CH3CHO (CH3)2CO

METHYL IODIDE: POTENTIAL TRACER OF MARINE CONVECTION IN GLOBAL METEOROLOGICAL MODELS

Loss by photolysis (~4 days), relatively uniform ocean source, large aircraft data base [D.R. Blake, UCI]

Cl-

Emission

hSimple modelfor ocean source DOC CH3I(aq)

MODEL AND OBSERVED CH3I(aq) FIELDS (r2=0.40)

Need to improve definition of source!