Trend Development of Precipitation-Ph in Central Europe

Summary

A critical investigation of literature reported precip-itation-pH measurements leads to the conclusion that since the late 30th the precipitation-pH has not changed very much in Central Europe, in spite of the fact, that the SO₂ emission has doubled in the meantime. This finding is confirmed by s₀me observations of the precip-itation-pH in Hamburg, which is measured since 1976 with an automatic precipitation monitor, operating continuously during falling precipitation. The pH shows no pronounced yearly cycle and no dependence of the wind direction, even in those cases where a trajectory analysis proves direct transport of the air mass over the North Sea without land contact. It is concluded, that acid formation during the precipitation process is limited due to physical and chemical reasons and that on the average, the removal capacity of the precipitation for acidifying gases is exhausted, when an average pH-value slightly above 4 is reached. As a consequence of increasing SO₂ emission a spreading out of the area with acid rain rather than a local decrease of the pH is predicted.