On the relation between pH and the chemical composition in atmospheric precipitation

Abstract

Based on chemical analyses of some 2 000 rainwater samples, the relation between the pH and the total amount of acid or of base respectively is studied. Considering the carbon dioxide-water system the theoretical relation between pH and total amount of acid or bicarbonate is calculated. A regular deviation is observed between the empirically found and theoretically calculated relation. Starting from chemical analyses of the most important compounds in atmospheric precipitation, a quantitative hypothesis is formulated of how these compounds originally were associated with acids or bases. It is further assumed that these have netralized each other and that the system has come to an equilibrium with the carbon dioxide pressure of the atmosphere. Good agreement is obtained between the predicted amount of acid or base and the measured one, and this is taken as a clear indication of the validity of the model. This model on the stoichiometric relation between acids and bases turns out to be a useful tool both for an interpretation of the amount of acid found in precipitation and in estimating future deposition of acid by precipitation.