We investigated the chemical characteristics of sea fog and its generation mechanism over the northwestern North Pacific from 28 June to 10 July 2001. Continuous aerosol number measurements revealed that sea fog scavenged coarse particles (d > 0.50 ¿m) more efficiently than fine particles (d < 0.50 ¿m). Although there was no relationship between Na+ concentration and sea fog age, anthropogenic ions concentrations (NO3-, nss-SO42-, and NH4+) decreased with an increase in sea fog age. Compared with nss-SO42- and NH4+, NO3- was selectively removed by sea fog. Coarse particles (sea-salt and NaNO3) act as condensation nuclei (CN) of sea fog droplets more preferentially than fine particles (H2SO4, (NH4)HSO4 and (NH4)2SO4) because of the effect of curvature. This is in harmony with the result of aerosol number measurement.