| Summary: | The issue of acid deposition and associated environmental problems has received special attention during recent decades and has been the subject of extensive research in a number of countries. However, there are no recent studies on acid deposition in Cardiff. Weekly rainfall samples were obtained from two urban areas in Cardiff from February 2006 to July 2007 and analysed for pH, electrical conductivity and major ions; SO42−, NO3−, Cl−, Ca2+, Na+, Mg2+, K+ and Pb2+. The chemical composition of precipitation was analysed in conjunction with meteorological variables to evaluate temporal and seasonal variations. Annual wet deposition was estimated, and enrichment factors determined. The pH of individual precipitations fluctuated excessively with a wide range from 4.9 to 6.6 indicating high variability in the acid sources and in neutralisation processes. Correlations between calcium and sulphate imply that CaSO4 may merge with the rainfall and neutralise the acidity. The volume-weighted mean concentrations of NO3− and non-sea salt SO42− were 24.1 and 31.4 μeq l−1, respectively. With the exception of the sea salt ions, no distinct spatial variations in ion composition were observed. Enrichment factors were calculated for most ions and higher correlation coefficients were obtained among most of the ions. Sea-derived material (Na+, Mg2+ and Cl−) showed pronounced cycles in concentration with maxima in autumn/winter. The Cl- (102 kg ha-1 yr-1) and Na+ (66 kg ha-1 yr-1) showed the highest wet deposition flux compared to the other ions. Anthropogenic and crustal sources made a significant contribution to both the acidification and neutralisation of precipitation in Cardiff. In all rain samples SO4-2 concentration exceeded NO3- concentration. Statistical analysis showed no significant differences in the physico-chemical parameters of the rainfall samples between the sites when tested at p<0.05. However, the ionic concentrations of wet precipitation depicted significant seasonal differences except for rainfall volume, K+, NO3- and SO4-2
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