Chemical and physical characteristics of rainfall in Venice: Influence of the sampling method on the reliability of the data

Abstract

From October 1985 to June 1987, a large number of samples of single precipitation events were collected in the city of Venice, with the purpose of acquiring reliable data on the acidity, electrical conductivity and chemical composition of the rain. The results obtained from analysis of the samples demontrate the occurrence in Venice of precipitation with pH values varying from 3.50 to 7.50. In particular, pH values <5.6 were measured in 76% of the cases, with the most frequent values ranging between pH 4.2 and 4.4. Examination of the correlations between the concentrations of Na +, Cl −1, H +, SO 4 2− and Ca 2+ ions, and of the seasonal trends of H +, SO 4 2− and NH 4 + emphasizes the influence of sea spray, of calcareous airborne particles and of the lagoon environment on the chemical composition of the rain. The suitability of the more common procedures of collection (bulk and wet-only collectors) and of storage of the rain samples used to obtain representative data was also evaluated. The wet-only sampler appeared to be the more reliable method for collecting the rain, provided that procedures assuring the stability of the chemical composition of the samples before analysis were respected.