Trends in summer sulphate in Europe

A trend analysis of the sulphate concentration in Europe in the summer half-year was performed. Data from various measuring networks were analysed, but only stations with quality assured sampling methods and a record of more than 10 years were included in the study. 1978 served as the reference year for the trend, because in that year most stations started operation. The relatively dense network in Belgium provided the most valuable data, as evidenced by the fact that two sites at a distance of only 10 km apart correlated better than 95% over a month. The two sites also show a correlation of better than 90% over a season with two other stations at distances of 45 and 95 km. The relative decrease in summer-sulphate at the four stations in Belgium, as analysed by linear regression, was 3.3% per year which corresponds to an absolute decrease of 0.42 mu g m(-3) per year. In the Netherlands the average yearly decrease in summer-sulphate at two stations was 3.5% (-0.34 mu g m(-3)). In other countries stations were further apart or only a single site was in use, which limits the representativeness of the data. In northwestern Germany, a region with several monitoring stations, a yearly averaged decrease of 3.0% occurred. The lower absolute decrease (0.25 mu g m(-3)) per year compared to that in the two neighbouring countries reflects the lower summer-time sulphate concentrations. In the remainder of Germany the average decrease was 1.6%. In South-Scandinavia the yearly relative decrease at two sites was 2.6% (0.13 mu g m(-3) absolute). There was no significant trend in the U.K. At the Polish station the levels increased, it decreased at the Hungarian and Austrian station and remained constant at the Czechoslovakian site. Reasons for omission of the data from France from the trend analysis are discussed. (C) 1997 Elsevier Science Ltd.