Marine aerosol particles from the Equatorial Pacific were studied usin
g transmission electron microscopy: Sea-salt aggregates consist largel
y of NaCl and Na-Ca sulfate crystals. Variations in the composition of
sea-salt aggregates occur, and these may reflect the effects of relat
ive humidity. There are several species of submicron, S-bearing partic
les, presumably including ammonium sulfate and strong acids. Diatom fr
agments are common, and sparse kaolinite and rutile crystals are the m
ineral component of this marine aerosol. The samples we studied appear
ed to be free of obvious anthropogenic effects.