The Swedish Precipitation Chemistry Network : Studies in network design usting the MATCH modelling system and statistical methods

In this study the Swedish Precipitation Chemistry Network has been examined thoroughly, including investigations into the representativeness of stations as well as into possibilities of time trend analysis. A suggestion of a new optimized network design is given. Using the MATCH modelling system, which has been developed as a tool for air pollution assessment studies, it has been possible to evaluate different hypothetical precipitation chemistry networks over Sweden. There is a clear indication from the different model experiments, focused on sulphur and nitrogen, that a proposed future reduction of the number of Swedish precipitation chemistry stations by about one third only has a small effect on the obtained annual and monthly wet deposition pattern over Sweden. Long-term changes in wet deposition can still be followed using this less dense station network. Comparisons with independent measurements indicate that errors in the MATCH system estirnates for sulphur and nitrogen are of the same size as for parallel measurements as long as the MATCH system has a sufficient number of high quality precipitation chernistry stations available for the region. A study of former results on wet deposition, using multivariate analysis, has clearly indicated that the base-cation deposition exhibits larger local variations than is the case for sulphur and nitrogen. Modelling of base-cation deposition is however not included in this study. The suggested reduction of the precipitation network is thus characterized by some caution, partly due to the base-cation deposition not being thoroughly investigated. Care has been taken not to diminish future possibilities in mapping base-cation deposition over Sweden