Heterogeneous sulfur conversion in sea-salt aerosol particles: the role of aerosol water content and size distribution |
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| Institution: | 1. University of Colorado at Denver, Center for Environemental Sciences and Department of Physics, 1200 Larimer Street, Denver, CO 80204, U.S.A.;2. National Oceanic and Atmospheric Administration, Air Resources Laboratory, Aerosol Research Section, Boulder, CO 80303, U.S.A.;3. University of Virginia, Department of Environmental Sciences, Clark Hall, Charlottesville, VA, U.S.A.;4. The Hebrew University, Department of Environmental Sciences, Jerusalem, Israel;1. I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany;2. Department of Physics, University of Calcutta, Calcutta 700009, India;1. Institute of Physical Chemistry, RWTH Aachen University, Landoltweg 2, D-52074 Aachen, Germany;2. Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), UMR 7583 (CNRS/Univ. Paris Est & Paris Diderot), Université de Paris Est, 61 avenue du Général de Gaulle, F-94010 Créteil cedex, France;1. Ashikaga Institute of Technology, 268-1 Omae-cho, Ashikaga, Tochigi 326-8558, Japan;2. Graduate School of Engineering, Ashikaga Institute of Technology, 268-1 Omae-cho, Ashikaga, Tochigi 326-8558, Japan;3. Niigata University, 8050 Igarashi-2nocho, Niigata, Niigata 950-2181, Japan;1. Department of Chemistry, University of Vermont, Burlington, VT 05405, USA;2. Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260, USA;3. Department of Chemistry, Penn State University, University Park, PA 16802, USA;4. Department of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125, USA;5. Division of Natural Sciences, New College, Sarasota, FL 34243, USA;6. Department of Chemistry, University of Virginia, Charlottesville, VA 22904-4319, USA;1. C.N.R. Institute of Atmospheric Pollution Research, Via Salaria, Km 29,300, Monterotondo St., Rome, 00015, Italy;2. Department of Chemistry, Sapienza University of Rome, P.le Aldo Moro, 5, Rome, 00185, Italy |
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| Abstract: | Meteorological and chemical conditions during the July 1988 Bermuda-area sampling appear to have been favorable for conversion of sulfur gases to particulate excess sulfate (XSO4). Observed average XSO4 and SO4 concentrations of 11 and 2.1 nmol m−3, respectively, at 15 m a.s.l. in the marine boundary layer (MBL) upwind of Bermuda, indicate that conversion of SO2 to XSO4, over and above homogeneous conversion, may be necessary to explain the > 5.0 average molar ratio of XSO4 to SO2. Given an observed cloud cover of <15% over the region and the <3 nmol m−3 SO3 concentrations observed by aircraft, heterogeneous conversion mechanisms, in addition to cloud conversion of SO2, are necessary to explain the observed 11 nmol XSO4 m−3.Aerosol water content, estimated as a function of particle size distribution plus consideration of SO2 mass transfer for the observed particle size distribution, shows that SO2 was rapidly transferred to the sea-salt aerosol particles. Assuming that aqueous-phase SO2 reaction kinetics within the high pH sea-salt aerosol water are controlled by O3 oxidation, and considering mass-transfer limitations, SO2 conversion to XSO4 in the sea-salt aerosol water occurred at rates of approximately 5% h−1 under the low SO2 concentration, Bermuda-area sampling conditions. All of the 2 nmol XSO4 m−3 associated with sea-salt aerosol particles during low-wind-speed, Bermuda-area sampling can be explained by this conversion mechanism. Higher wind speed, greater aerosol water content and higher SO2 concentration conditions over the North Atlantic are estimated to generate more than 4 nmol XSO4 m−3 by heterogeneous conversion of SO2 in sea-salt aerosol particles. |
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