Aspects of wet, acidifying deposition in Arnhem: Source regions, correlations and trends (1984–1991)

Abstract

A time series of wet deposition in Arnhem, the Netherlands, was analysed for the period 1984–1991. Precipitation was collected with four samplers on a daily basis. A comparative study by the Dutch National Precipitation Network showed significant biases for the observations of the National Network station due to longer exposure to dry deposition. Simultaneous operation of wet-only and bulk collectors demonstrated a concentration bias of about 10% for daily bulk sampling. Using a cluster analysis of backward trajectories, clear distinctions could be made between precipitation from continental and maritime origin. Event-to-event variations in deposition seemed to be determined largely by meteorological influences. As major anthropogenic source regions, the U.K., France, Belgium and the Netherlands itself were identified. The contribution of Dutch sources to wet acid deposition in Arnhem was estimated at 30–40%. Trends and seasonal variations were analysed with an advanced time-series model based on Kalman filtering. Similar seasonal variations were found for SO 4 2− and NH 4 +. Also, seasonal variations in the concentrations of H + and NO 3 − corresponded. Significant long-term changes in deposition and concentration were found for SO 4 2− (about −3% yr −1) and H + (about −9% yr −1) only. The analysed trends were decreasing, but decreases were larger in the years 1984–1986 than in the following years. The relative decrease in the wet deposition of SO 4 2− was substantially smaller than decrease in dry-deposited SO 2 and SO 4 2−.