Historical change in precipitation pH at Kobe, Japan: 1935–1961

Historical change in precipitation pH was successfully recovered by analyzing pH records for Kobe, Japan, from 1935 to 1961. This represents the oldest and the longest data set in Asia. The pH rose gradually by 1.0 pH unit from 1938 to 1945 and then declined steeply to less than pH 5.0 in 1952. A semi-quantitative index was employed for the analysis because the data quality was not sufficient to obtain conventional annual averages. It was also suggested that the pH at Kobe in the early 1950s was as low as the current pH. These results present evidence for early acidification in Asia.