AN ATMOSPHERIC CHEMIST’S VIEW OF THE WORLD FiresLand biosphere Human activity Lightning Ocean physics chemistry biology

“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 values over Europe: ocean sink? southern Sweden [Solberg et al., 1996] High values over South Pacific: ocean source? South Pacific [Singh et al., 2001]

ROLE OF OCEAN IN ATMOSPHERIC BUDGET OF ACETONE Biological uptake (Kieber et al., 1990) SINK? H 298 = 30 M atm -1 ; physical uptake limited by both gas- and aqueous-phase transfer h organic microlayer SOURCE? Zhou and Mopper (1997) measurements of oceanic acetone are very few!

Observed atmospheric concentrations (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 estimate of sources/sinks A priori best estimate of sources/sinks (with errors)

GLOBAL 3-D MODEL SIMULATION OF ATMOSPHERIC ACETONE a priori sources/sinks Optimized 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 BUDGETS OF A RANGE OF MODERATELY SOLUBLE GASES Species Atm lifetime H Atm lifetime m OceanML /m Atm (chemical loss) (M atm -1 ) (ocean uptake) ( Henry’s law, dimensionless) Acetone 20 days days 10 Methanol 17 days days 80 HCN 2.5 years days 5 Assuming ocean T = 283K, ML depth = 50m, surface wind U = 5 m s-1 T-dependent!

ATMOSPHERIC COLUMN OBSERVATIONS OF HCN SHOW 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 make significant 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 without marine source PAN HCHO CH 3 CHO (CH 3 ) 2 CO

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 h Simple model for ocean source DOC CH 3 I(aq)

MODEL AND OBSERVED CH 3 I(aq) FIELDS (r 2 =0.40) Need to improve definition of source!