HR: 17:30h
AN: A42F-07    [PDF]
TI: Modeling and measurements of oxygen isotope tracers of sulfate formation: Implications for the sulfur budget in the marine boundary layer
AU: * Alexander, B
EM: balexand@fas.harvard.edu
AF: Harvard University, 29 Oxford Street, Cambridge, MA 02138 United States
AU: Savarino, J
EM: jsavarino@lgge.obs.ujf-grenoble.fr
AF: CNRS/UJF Laboratoire de Glaciologie et Geophysique de l'Environment, 54 rue Moliere, BP 96, St. Martin d'Heres, 38 402 France
AU: Lee, C C
EM: charles_ c_lee@urscorp.com
AF: University of California, San Diego, 9500 Gilman Drive Mail code 0356, La Jolla, CA 92093 United States
AU: Lee, C C
EM: charles_ c_lee@urscorp.com
AF: URS Corporation, 911 Wilshire Boulevard, Los Angeles, CA 90017 United States
AU: Park, R
EM: rpark@fas.harvard.edu
AF: Harvard University, 29 Oxford Street, Cambridge, MA 02138 United States
AU: Jacob, D J
EM: djacob@fas.harvard.edu
AF: Harvard University, 29 Oxford Street, Cambridge, MA 02138 United States
AU: Yantosca, R
EM: bmy@io.harvard.edu
AF: Harvard University, 29 Oxford Street, Cambridge, MA 02138 United States
AU: Thiemens, M H
EM: mthiemens@chem.ucsd.edu
AF: University of California, San Diego, 9500 Gilman Drive Mail code 0356, La Jolla, CA 92093 United States
AU: Chin, M
EM: chin@rondo.gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, Code 916, Greenbelt, MD 20771 United States
AB: Measurements of the mass-independent fractionation (MIF) in the oxygen isotopes of sulfate provide information on the relative oxidation pathways of sulfate formation(Savarino et al. 2001). The oxidation pathway has important implications for the effect of sulfate aerosols on climate, because it regulates whether this process can form a new particle in the atmosphere (gas-phase oxidation by OH) or forms on an already existing particle (aqueous-phase oxidation by $H_{2}O_{2}$ and $O_{3}$). Both present and past measurements of the MIF of sulfate show that $O_{3}$ is an important aqueous-phase oxidant in the sulfur cycle with regional (Lee, 2001), climatic (Alexander et al., 2001) and anthropogenic (Alexander et al., in preparation) variations. However, most global climate models do not consider $O_{3}$ to be an important oxidant for sulfate formation, primarily due to the assumption that most aqueous-phase oxidation of $SO_{2}$ occurs in clouds with pH values at which $H_{2}O_{2}$ will be the dominant aqueous-phase oxidant. Oxidation on alkaline aerosols such as sea salt or mineral dust could provide this missing $O_{3}$ oxidation pathway, as has been previously suggested in the literature. We report measurements of the MIF of sulfate collected on aerosol filters from two INDOEX cruises that show large $\Delta^{17}O$ values in the ITCZ region of the Indian Ocean. These measurements are compared with results from the GEOS-CHEM model of atmospheric chemistry and climate. The $\Delta^{17}O$ values of sulfate in the GEOS-CHEM model are calculated off-line based on the relative sources of sulfate. In addition to gas-phase oxidation by OH and in-cloud oxidation by $H_{2}O_{2}$ and $O_{3}$, $O_{3}$ oxidation of S(IV) on alkaline sea salt aerosols has been implemented in the GEOS-CHEM model. Results from the model indicate that the large $\Delta^{17}O$ values of sulfate measured within the ITCZ can be explained by oxidation of S(IV) by $O_{3}$ on sea salt aerosols. This process can affect the predicted climate forcing of sulfate aerosols by perturbing the amount of sulfate formed through gas-phase oxidation, and also by affecting the lifetime of sulfate that forms on coarse aerosols. The implications of this change on the sulfur budget in the marine boundary layer will be discussed.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 1040 Isotopic composition/chemistry
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting