A method to determine rainwater solutes from pH and conductivity measurements

An established method to calculate the acid fraction (AF= [H+]/[An]) of substances dissolved in an aqueous solution solely based on the measurement of the pH-value and the electrical conductivity is extended to determine in addition the total solute concentration. The loading of samples of atmospheric hydrometeors can be assessed from these four parameters (total dissolved material, acid fraction, pH and electrical conductivity). Mean electrical conductivities, the fundamental parameters of the method, are presented for rainwater from marine, coastal, rural and mountain sampling sites. The accuracy of the method is confirmed by comparing solute concentrations and acid fractions of various samples of rainwater, determined on the one hand by the method proposed here and on the other hand by ion chromatography. Annual average values of pH, electrical conductivity, total dissolved material and acid fraction are presented for rainwater from coastal, rural and mountain sampling sites located in Germany as an example of an application of the new method proposed here. The observed solute concentration decreases from the North to the South. The acid fraction is lowest at the coast (10% on average), rising to about 20% at the rural and 25% at the mountain sites.