What is the Size- and Composition-Dependent Production Flux of Sea Spray Aerosol and Why do we Care? Schwartz, S. E.. American Geophysical Union Ocean Sciences Meeting, Portland OR, February 22, 2010, IT11B-06. Invited.

Sea spray aerosol (SSA) particles are created mainly by bursting of bubbles at the sea surface following wave breaking and resultant entrainment of air into the water column. These particles contribute to light scattering, serve as media for uptake and reaction of trace gases, and are a major source of cloud condensation nuclei, thereby affecting the microphysical and radiative properties of marine clouds. Knowledge of the processes controlling the abundance and size distribution of SSA particles is essential to describing their optical and cloud nucleating properties in the unperturbed and anthropogenically perturbed marine atmosphere and to quantifying anthropogenic perturbations. Central to this understanding is knowledge of the flux of SSA particles from the ocean surface to the atmosphere as a function of particle size, of the size-dependent composition of these newly produced particles, and of the dependence of these quantities on controlling chemical and physical variables. Until the past few years attention has been paid mainly to the production flux of larger particles, radius at 80% relative humidity r80 > 100 nm, because of the dominance of such larger particles to the mass, light scattering, and cloud nucleating properties of this aerosol. Present formulations of size dependent production flux are uncertain to factors of several fold (Lewis and Schwartz, AGU Monograph, 2004) with consequent implications for modeled atmospheric concentrations of SSA and resultant sensitivity of cloud albedo to perturbations by anthropogenic aerosols. Recent field measurements and laboratory studies with actual seawater indicate a large number flux of smaller particles, diameter as low as 10 nm. These particles appear to be considerably enriched in organic matter, a likely consequence of concentration of surfactant at the air-water interface of bubbles, suggesting that the cloud nucleating and optical properties of these particles may differ substantially from those of particles having the composition of bulk seawater. This talk reviews recent laboratory, field, and modeling studies and examines the sensitivity of modeled SSA loading and properties to assumptions regarding the SSA production flux.


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