Experimental study of the scavenging process by means of a sequential precipitation collector, preliminary results

Abstract From January 1986 to July 1989, 103 rain events were sampled with a sequential collector in Vitoria, a moderately industrialized city (Spanish Basque country). Each sample was analysed in terms of pH, conductivity and the ionic concentration of Cl − , NO − 3 , SO 2− 4 , NH + 4 , Na + , K + , Ca 2+ and Mg 2+ . On average, the rainwater samples were acid, with a mean pH value of 4.9 the major ions being SO 2− 4 and Ca 2+ . Events with highly acid characteristics (pH ⩽ 4.5) represent 14% of the total collected. Analysis of meteorological conditions in relation with the average ionic concentrations points out the influence of anthropogenic sources from southwestern France and from the northern Basque country. The decrease in the wet deposition (in percentage of the total deposition per rainfall event) throughout precipitation is particularly apparent for NH + 4 and Ca 2+ ions. In precipitation related to the meteorological Local-class, the atmospheric removal appears to be more efficient, especially for Ca 2+ , and we can also note a precipitation-neutralizing effect. Precipitation scavenging is mainly controlled by the total amount of water precipitated. However, the intensity of the rain modified the deposition rate.