Speaker: Dr. Daniel A. Knopf
Professor, School of Marine and Atmospheric Sciences, Stony Brook University
2003 Ph.D., Swiss Federal Institute of Technology (ETH), Inst. for Atmospheric and Climate Science, Switzerland

Sea spray is a major source of atmospheric aerosol mass over much of the earth’s surface. Knowledge of its composition and cloud formation propensity are critical for determining its role in atmospheric chemistry and climate. In absence of other airborne ice nucleating particles such as mineral dust, sea spray aerosol (SSA) may contribute significantly to atmospheric ice cloud formation. Only recently it has been recognized that SSA is associated with organic matter. SSA particles collected in the field and from laboratory mesocosm experiments are physicochemically characterized using, e.g., scanning transmission X-ray microscopy with near edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS). These analyses reveal that SSA consist of an inorganic core coated with biogenic material. NEXAFS spectra and spectrophotometric methods based on staining support the presence of polysaccharidic and proteinaceous material stemming from phytoplankton exudate. This exudate material can induce ice formation at tropospheric relevant conditions, providing a link between marine biological activity and cloud formation, thus climate. However, the nature of this marine biogenic material and its physicochemical properties resulting in observed ice nucleating propensities are not well understood and will be discussed in this seminar.