THERMODYNAMIC AND OPTICAL-PROPERTIES OF SEA-SALT AEROSOLS

Sea salt particles are constantly produced from ocean surfaces by wave -wind interactions and removed by deposition and precipitation scaveng ing. These particles constitute the background aerosol for light scatt ering in the marine boundary layer. In this work, the thermodynamic an d optical properties of sea salt aerosol particles generated from seaw ater samples are measured at 25 degrees C as a function of relative hu midity, using a single-particle levitation technique. Water activities , densities, and refractive indices of aqueous solution droplets conta ining a single salt NaCl, Na2SO4, MgCl2, or MgSO4 are also reported as a function of concentration. The light-scattering properties of the s ea salt aerosol are modeled by the external mixture of these four salt systems selected to approximate the sea salt composition. Good agreem ents are obtained. It follows that in either visibility reduction or r adiative forcing calculations, both freshly produced and aged sea salt aerosols may be modeled by external mixtures of the appropriate inorg anic salts, whose solution properties are now available in the literat ure.