The horizontal gradient concentrations of particulate and gaseous pollutants were measured on the western coast of the Iberian Peninsula. In summer, a large fraction of particulate sea-salt chlorine (67% for fine particles and 24% for coarse particles) is already lost during the sea breezes by the time marine air masses arrive to the coast. The volatilization values increase to 86% and 68%, 30 km inland. Acidic sulphur compounds are responsible for 64--71% of the degassing of Cl from fine particles, while nitric acid is the main cause of the coarse particles, contributing with 60--68% for the particulate chlorine loss. There is more or less an 11% chlorine degassing per hour during the air mass transport inland. Thermodynamic equilibrium is not attained during the first 3 hours of aerosol transport inland for both fine and coarse sea-salt particles. ¿ 1998 American Geophysical Union