Rainwater samples collected on the northwestern coast of Washington State have excess sulfate concentrations which are similar to other remote marine sites. Simultaneous sampling of submicrometer aerosol particles and rainwater in meteorologically selected marine air masses shows that the sulfuric acid component of these particles is sufficient to account for the observed rainwater sulfate via the process of nucleation scavenging based on an effective liquid water content (Leff); its small range and realistic magnitude support this conclusion. Equilibrium modeling based on aerosol sulfate and Leff predicts a rainwater pH of 5.2 compared to the measured pH to 5.1 ¿ American Geophysical Union 1988