OZONE OXIDATION OF SULFUR IN SEA-SALT AEROSOL-PARTICLES DURING THE AZORES MARINE AEROSOL AND GAS-EXCHANGE EXPERIMENT

Sea-salt aerosol particles in the lowest tens of meters above the ocea n are, typically, more than three-fourths water on a volume basis. Cal culations herein indicate that aqueous-phase conversion of sulfur diox ide dissolved in the water associated with sea-salt-particles (sea-sal t aerosol water) supported the production of 2-8 nmol m(-3) of non-sea -salt sulfate (nssSO(4)(=)) during the Marine Aerosol and Gas Exchange (MAGE) experiment intensives. This production is based on ozone oxida tion of dissolved SO2 in sea-salt aerosol water and accounts for sulfu r gas and ozone mass transfer limitations as a function of sea-salt pa rticle size. Measurements showed that 1-15 nmol m(-3) of nssSO(4)(=) w as actually present in the sea-salt particle mode except for four enha nced concentration cases due to continental sulfur input. The range in predicted, as well as observed, nssSO(4)(=) was primarily due to vari ability in sea-salt aerosol water volume. The nssSO(4)(=) produced by ozone oxidation of sulfur dioxide, being in the sea-salt particle mode with observed volume geometric median diameter of 3.5-5 mu m, is dry deposited at a fairly rapid rate. The remainder, being large-particle cloud condensation nuclei, may contribute little to cloud albedo over the global oceans. The two papers following this one, Kim et al. (this issue) on aerosol size distribution and water content and Parfai et a l. (this issue) on compositional variations of sea-salt-mode aerosol p articles observed by electron microscopy, complement and support resul ts presented here. All three present results of the MAGE experiment an d precede a forthcoming special issue of the Journal of Geophysical Re search-Atmospheres on MAGE (B. Huebert, guest editor).