Sulfate in precipitation as observed by the European atmospheric chemistry network

The temporal variation in sulfur concentration/deposition involves long term fluctuations which show striking similarities within certain areas but are different between areas in different positions relative to major sulfur emission areas in Europe. As an example, the deposition has been constant or decreasing during the last ten years in most of the area covered by the network, indicating that an increasing amount of the sulfur emitted in Europe is transported and deposited elsewhere, possibly in an eastward direction.The seasonal variation in deposition resembles that for amount of precipitation and shows a maximum during the summer or autumn for most areas. The concentration shows a maximum in the spring and a minimum in the autumn at most stations.The concentration field has a maximum approximately over Belgium and Holland with decreasing concentrations towards SW to NE (over W) but with comparatively high levels extending up over Finland. (Areas to the east and south are not covered by the network.)The deposition field was, based on a brief discussion of the relation between concentration and amount of precipitation, obtained as the product of these latter fields. High deposition rates are found in the south of Norway and in the middle of Britain in addition to the areas with high concentration.Sulfur and hydrogen ion are the dominating ions in precipitation followed by ammonium and nitrate except in coastal areas and in places where the soil is bare.Sources of errors in the data base are discussed and the results from a large number of additional sampling sites around and between the regular network sampling sites are most helpful in this regard. These latter measurements also permit an estimate of the uncertainty in areal concentration averages which are due to local and mesoscale variability.Finally, past and future importance of continuous measurements (as in the EACN) is discussed briefly.