Trace element deposition and trends during a ten year period in Finland.

The deposition of aluminium, arsenic, cadmium, chromium, copper, iron, lead, manganese, nickel, vanadium and zinc in bulk precipitation was examined at eight background stations in Finland during the last 10 years (1998-2007). The annual deposition was from the lowest values to the highest Cd<As<Cr<Ni<V<Cu and Pb<Mn<Zn<Al<Fe. Most of the elements had a south to north decreasing gradient mainly due to minor domestic emissions in the north, growing distance to the large European source areas and differences in the length of snow-cover period. Element enrichment factors divided the trace elements to the following categories: (1) slightly enriched Cr, Fe and Mn; (2) moderately enriched Cu, Ni and V; and (3) highly enriched As, Cd, Pb and Zn. Trend analysis of annual depositions showed that the established decreasing trend in As and Pb deposition continued during our study period while Cr, Cu and Fe depositions have lately increased. No statistically significant trends were detected for Cd, Mn, Ni, V and Zn during the studied years. Additionally, the measurement uncertainty of trace elements was evaluated for the whole measurement chain.