The Swedish network

The first major precipitation chemistry program was initiated by Swedish scientists (see Egner and Eriksson, 1955). The network was extended to the northern and western parts of Europe and for some time chemical data were published in the scientific journal Tellus. At the beginning of the sixties more than one hundred stations were involved in the network. This network is still in operation, and it is now called the European Atmospheric Chemistry Network (Granat, 1978), since not only precipitation chemistry is measured in this program (see Egner et al., 1955). The number of stations at present is about 50. Monthly precipitations samples are collected by open rain gauges. 

Concerning possible damage caused by atmospheric precipitation to other media of our environment (e.g. lakes, soil, vegetation), the acidity or pH of precipitation water is of crucial interest. It should be noted here that the neutral point of atmospheric waters is lowered by the presence of COz in the air. Thus, it can be calculated (Junge, 1963) that the neutral point is at pH = 5.6 at a temperature of 

This hydrogen ion concentration is then altered by different trace constituents. 

The spatial and temporal distribution of pH in precipitation over Scandinavia was first studied by Barrett and Brodin (1955). According to their data, in South Sweden and in seaside areas, the pH is between 4 and 5 in the majority of cases. In a more continental environment the pH reaches the value of 6. The above authors 

Distribution oT chloride concentration of precipitation water over North and North-West Europe (Junge. 1963). (By courtesy of Academic Press and the author) 

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Figure 48 illustrates the spatial distribution of chloride ions measured by the Swedish network in 1957 and 1958 (Junge, 1963). In this figure the results of a Czechoslovakian program performed during the International Geophysical Year (Macku et al., 1959) are also included. One can see that the isolines practically follow the contour of the continent which makes evident that in locally unpolluted air the atmospheric chloride is of maritime origin. In Scandinavia the concentration initially decreases exponentially with distance from the ocean and reaches a rather constant value. 

This gives SJ over 16 000 operating years of ATC experience.The ATC is applied on about 60% of the Swedish network, carrying more than 95% of the total traffic. The Swedish network is about 11000 km long. 

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