More than 25 years of data on sulfate in precipitation from the European Air Chemistry Network (EACN) are analysed for seasonal and long-term trends and their spatial variability. The number of stations has varied between about 50 and 100, all of them located in the central and northern parts of western Europe. Despite considerable shortcomings of the data (indicated among other things by poor ionic balance during several years, particularly in the late 1950s and the early 1960s) the following conclusions are drawn.

In Norway, Sweden, Denmark and Finland, the sulfate concentration increased by roughly 50 per cent between the late 1950s and the late 1960s. A further increase during the 1970s is indicated at the Danish stations but most stations in Sweden and Norway show a decline by on the average about 20 per cent since the early 1970s. Sulfate data from the U.K. and the European continent seem to exhibit less systematic variations.

A comparison between the long-term changes in the Scandinavian data on sulfate in precipitation and the corresponding changes in anthropogenic SO2 emission in Europe indicates a fair agreement with regard both to the increase in emission during the 1950s and 1960s and, except for the Danish stations, also the subsequent decrease in emission in several of the West European countries.

In most parts of the network the annual cycle of concentration of sulfate exhibits a maximum in February through May and a minimum in July to October, whereas the wet deposition normally has its maximum in May to August and minimum in December to March. A comparison with the annual cycle of anthropogenic emission, which has a clear maximum in December to March, indicates that the fraction of sulfur exported out of the region is larger in winter than in summer.

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