Measurements of the chemical composition of marine aerosol were made at a location on the north-west coast of the continental United States. The average concentration of sulfate ion in submicrometric aerosol particles was 0.4 μg m-3. The average ammonium ion to sulfate ion molar ratio was 1.0 and was nearly the same as the ratio of 1.1 for concurrently collected rain samples. There was a large variability in these parameters on the 3--hour basis of the measurement method. ¿ American Geophysical Union 1988