The Chemical and Physical Characteristics of Fresh Aerosols Produced at the Ocean Surface *Long, M S [email protected] Keene, W [email protected] Maben, J [email protected] Department of Environmental Sciences, University of Virginia, 280 Clark Hall, Charlottesville, VA 22908 US Kieber, D [email protected] Davis, A J [email protected] Dahl, E [email protected] State University of New York College of Environmental Science and Forestry, 1 Forestry Drive, Syracuse, NY 13210 US Maring, H [email protected] NASA Headquarters, Science Mission Directorate Mail Suite 3F71, Washington, DC 20546 US Pszenny, A [email protected] Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, 39 College Road, Durham, NH 03824 US and Mount Washington Observatory, PO Box 2310, North Conway, NH 03860 US Izaguirre, M [email protected] University of Miami, Rosenstiel School of Marine and Atmospheric Science, Miami, FL 33149 US Zhou, X [email protected] Wadsworth Center, NYS Department of Health, and School of Public Health, SUNY at Albany, Empire State Plaza P.O. Box 509, Albany, NY 12201-0509 US Fresh aerosols produced by wind stress at the ocean surface undergo rapid multiphase chemical and physical transformation. Consequently, it is impossible to unequivocally differentiate primary versus secondary constituents based on measurements of aerosols in ambient marine air. However, reliable characterization of the initial aerosol composition is essential to interpret the nature of subsequent chemical processing, associated biogeochemical cycles, and related environment influences. Fresh marine aerosols were generated artificially by bubbling zero-air through a 1.3 m column of flowing seawater within a 20-cm diameter Pyrex and Teflon chamber deployed at Bermuda. Aerosols produced by bursting bubbles at the surface were swept with zero-air hydrated to ~80% RH through isokinetic ports and subsequently sampled in bulk and with MOUDI cascade impactors for analysis of major ions, total halogens, and organic carbon (OC) and with Aerodynamic Particle Sizer (TSI Model 3310) and a Scanning Mobility Particle Sizer (TSI Model 3934L) for characterization of number size distributions (13 nm to > 15 micrometer diameters). The composition of feed seawater was measured in parallel. The median OC concentration (65 micrometer) and ratios of OC to sea-salt constituents in feed water were virtually identical to long-term averages for surface seawater offshore. Relative size distributions of conservative sea-salt aerosol constituents were similar to those over the open ocean. Ratios of major ions and of total Cl and Br in all size fractions were statistically indistinguishable from those in surface seawater. OC was highly enriched relative to seawater in all size fractions (median factor for all samples = 387); highest enrichments were associated with sub-micron size aerosols. Number size distributions were bimodal with peaks at 4 to 5 micrometer and 120 to 130 nm diameter. About 95 % of the inorganic sea-salt mass was associated with super-um size fractions; OC dominated the sub-micron size fractions. The efficient mechanical production of primary sub-micron marine aerosols has important implications for multiphase chemical processes in the marine troposphere and associated radiative effects.