Methods for the validation of precipitation pH: applications to Texas data

Abstract Methods for the validation of reported pH values are developed for incomplete precipitation chemistry data sets. The most stringent tests are based on a comparison between the net strong acidity calculated from the the conservative inorganic cations and anions and that determined from the measured pH. The strong acidity of a sample in equilibrium with atmospheric carbon dioxide can be determined from an accurate pH measurement. Less severe tests are based on charge and conductivity balances. The proposed methods are applied to Texas precipitation chemistry data to identify unreliable measurements and to determine the spatial distribution of the mean pH for validated data. Reported mean pH values, especially those of pH > 5, are lower than can be validated. For data sets with a complete analysis of the major ionic species, the comparison of net acidities is generally a stronger quality assurance test for the validation of pH measurements than the charge balance.