168 HILL 



Data reported in Engstrom's study for the year 1965 show that the excess 

 acid* in precipitation in Scandinavia closely paralleled deposition of excess 

 sulfate in precipitation (Fig. 2), and during the past 15 years intrusion of excess 

 acidity into southern Scandinavia from a southwesterly direction has been 

 increasing (Fig. 3). The pH of rainwater 20 during this time period was found to 

 be as low as 2.8. Acidity in rainfall may be at least in part responsible for the 

 fact that many lakes and rivers in Sweden are increasing in acidity (Fig. 4). 



Acid groundwater may lead to leaching of nutrients required for growth of 

 agricultural and forest vegetation, leading to reduced productivity. Microbial life 

 may also be affected. If present trends continue, the pH of lakes in Sweden 

 evidently will within a foreseeable time reach a level critical for the life of fishes. 



Of great interest is the question of the origin of the acidity in precipitation 

 found in Scandinavia. Several kinds of circumstantial evidence point to 

 man-made emissions of SO2 in northern and western Europe. First, as stated by 

 Engstrom, the estimated deposition of anthropogenic sulfur in precipitation 

 within Sweden exceeds the anthropogenic emission from Sweden. This is also the 

 case for Norway, but the opposite is found in Denmark, Holland, West Germany. 

 France, and the United Kingdom. Second, also in Engstrom's report, an 

 air-parcel trajectory analysis is described in which the end points of a large 

 number of 24- and 60-hr trajectories were determined for parcels originating 

 from a single point in north central Europe. It was found that the end points 

 were fairly symmetrically distributed around the point of origin but with a drift 

 of the center of gravity to the east and northeast. Third, Reiquam 21 ' 22 has 

 applied an air-pollution simulation model to the region. The model was 

 developed to treat regional air-pollution episodes in which relatively stagnant air 

 masses develop and persist over a large area for several days. The region is 

 considered to be laid out on a square grid with a grid spacing in the case of the 

 calculation of interest of 2 of latitude and longitude. Over each square a box 

 was visualized, which for the calculation of interest was 3 km high, correspond- 

 ing to the assumed mixing depth of the atmosphere. The air within each box was 

 assumed to be well mixed. Sulfur emissions were tabulated for each box on the 

 basis of fuel-consumption data for the region and an assumed sulfur emission of 

 2.5% of the fuel burned. Simple mass balances were devised which used the 

 emission data and mean values of local wind velocity to compute the movement 

 of pollutant sulfur from box to box. The distribution of total sulfur 

 concentration in the air over northern and western Europe as calculated at the 

 end of a simulated 10-day wintertime episode of light southwesterly wind is 

 shown in Fig. 5(a). The effects of cessation of operation of sources in the United 

 Kingdom and in northern Europe are shown in Figs. 5(b) and 5(c). Reiquam 

 noted that his model did not take into account chemical transformation in the 

 atmosphere, processes of removal at the earth— air interface, especially precipita- 



The term "excess acid" is defined as the total acidity in precipitation over the time 

 period of 1 year minus the total amount of base. 



