GRAVIMETRIC ANALYSIS, IONIC COMPOSITION, AND ASSOCIATED WATER MASS OFTHE MARINE AEROSOL

Measurements of the total aerosol mass and ionic composition were obta ined for submicrometer (D-p less than or equal to 1.0 mu m) aerosol pa rticles from the remote Pacific boundary layer by gravimetric and ion chromatography analysis. Discrepancies were found to exist between the absolute mass determined by the separate techniques suggesting aeroso l components in addition to sea salt and sulfate particles exist at si gnificant mass concentrations. The gravimetric mass was equal to or si gnificantly larger than the sum of the ionic masses, suggesting additi onal aerosol components contribute between 0 and 75% of the submicrome ter aerosol mass. Measurements of the elemental composition of individ ual particles by electron microscopy confirmed the presence of mineral and carbonaceous particles which contributed 0-86% of the total numbe r concentration for the particle-size range of interest. The relative number of submicrometer sulfate particles with respect to the total wa s low during periods with the largest discrepancy between the gravimet ric and ionic mass. The amount of water associated with the submicrome ter aerosol at 47% relative humidity made up 29% of the total aerosol mass collected on the filters (and 9% of the total mass at 35%). Labor atory studies determined the relative amount of water associated with sea salt, sulfate, and sodium chloride particles on a filter substrate , with sea-salt particles containing 27% water and ammonium sulfate pa rticles containing only 4% water at 40% r.h.