TY  - JOUR
AU  - Alexander, B.
AU  - Park, R. J.
AU  - Jacob, D. J.
AU  - Li, Q. B.
AU  - Yantosca, R. M.
AU  - Savarino, J.
AU  - Lee, C. C. W.
AU  - Thiemens, M. H.
PY  - 2005//
TI  - Sulfate formation in sea-salt aerosols: Constraints from oxygen isotopes
T2  - J. Geophys. Res.
JO  - Journal of geophysical research-atmospheres
VL  - 110
PB  - American Geophysical Union
KW  - atmospheric chemistry
KW  - aerosol formation
KW  - isotopes
KW  - 0305 Atmospheric Composition and Structure: Aerosols and particles
KW  - 0312 Atmospheric Composition and Structure: Air/sea constituent fluxes
KW  - 0365 Atmospheric Composition and Structure: Troposphere: composition and chemistry
KW  - 0490 Biogeosciences: Trace gases
KW  - 1041 Geochemistry: Stable isotope geochemistry
N2  - We use observations of the mass-independent oxygen isotopic composition (?17O) of sulfate in the marine boundary layer (MBL) to quantify the sulfate source from aqueous SO2 (S(IV)) oxidation by O3 in alkaline sea-salt aerosols. Oxidation by O3 imparts a large ?17O signature to the resulting sulfate (8.8‰) relative to oxidation by H2O2 (0.9‰) or by OH or O2 (0‰). Ship data from two Indian Ocean Experiment (INDOEX) cruises in the Indian Ocean indicate ?17O values usually <1‰ in the submicron sulfate aerosol but considerable variability in the supermicron sulfate with frequent occurrences above 1‰ and up to 6.7‰. The large ?17O values are associated with high concentrations of sea-salt aerosols, providing evidence for the S(IV) + O3 pathway. We use a global chemical transport model (GEOS-CHEM) to interpret quantitatively the INDOEX observations and to assess the global importance of sulfate production in sea-salt aerosols. The model accounts for titration of sea-salt alkalinity in the MBL by uptake of acid gases (SO2, H2SO4, and HNO3), shutting down the S(IV) + O3 pathway. We find that this titration occurs rapidly over much of the oceans except at high latitudes (strong sea-salt emission) and is due to both the S(IV) + O3 reaction and HNO3 (g) condensation; that is, sulfate formation in sea-salt aerosols is limited by the alkalinity flux from the ocean and by competition for this alkalinity supply from HNO3 (g). The model is consistent with the ?17O magnitudes and patterns in the INDOEX data. Titration of alkalinity is critical for the success of the model simulation. Regeneration of sea-salt aerosol alkalinity by OH uptake is inconsistent with the ?17O observations in INDOEX. Model results indicate that sulfate production in sea-salt aerosols decreases MBL SO2 concentrations and gas phase H2SO4 production rates by typically 10–30% (up to >70%) and increases MBL sulfate concentrations by typically >10% (up to 30%). Globally, this mechanism contributes 9% of atmospheric sulfate production and 1% of the sulfate burden. The impact on H2SO4 (g) formation and implications for the potential formation of new particles in the MBL warrants inclusion in models examining the radiative effects of sulfate aerosols.
SN  - 0148-0227
UR  - http://dx.doi.org/10.1029/2004JD005659
N1  - exported from refbase (http://publi.ipev.fr/polar_references/show.php?record=5554), last updated on Tue, 21 Apr 2009 12:03:18 +0200
ID  - Alexander_etal2005
ER  -