The nature and extent of acid precipitation is reviewed. Studies have shown that significant decreases in the pH of rain have occurred in Scandinavia and the northeastern United States during the last two decades. This increased acidity correlates well with anthropogenic activities that emit acidifying substances into the atmosphere. Problems of measurement and interpretation are discussed. Finally, a review of acid precipitation's impact on surface waters and on soils is presented.

Based on data from the Swedish water quality covering 78% of the Swedish area, the discharge of sulphur has been computed for the period 1969 to 1977. The trend for this period gives a figure for 1977 of 660,000 tons per year. This figure exceeds that of the atmospheric fallout by about 200,000 tons per year. The different items contributing to this difference are discussed. The increase of the discharge of sulphur during the investigated period varies from 2 to 5% per year in the different regions of Sweden. Due to the storage characteristics of the soil-water reservoirs the increase of the input of sulphur must be larger than these figures. The discharge of sulphur from different parts of Sweden during this century has been reconstructed. The total figure in excess of a geochemical reference amounts to about 60 million tons of sulphur. In parts of the South and West of Sweden the annual deposition of sulphur amounts to about 25 kgs per ha. Rough figures of the so-called biogenic sulphur can be given for Sweden along with a geochemical reference value. The application of these figures to the increasing acidification of Sweden is obvious.

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