Organic acids in springtime wisconsin precipitation samples

A short-term study on organic acids in precipitation was conducted from 15 March to 1 June 1984 at two sites on the Wisconsin Acid Deposition Monitoring Network. Aliquots of collected samples were fixed with tetrachloromercurate (TCM) and analyzed for low molecular weight organic anions via ion-exclusion chromatography (ICE). Unfixed aliquots were subjected to standard network inorganic analyses. Of the 31 samples collected, 30 contained detectable concentrations of formate and acetate ions, with concentrations ranging from < 0.43 to 56μmol ℓ⁻¹ for the former and < 0.83 to 33 μmol ℓ⁻¹ for the latter. Propionate, oxalate and malonate ions were also detected in a number of samples. Statistical analysis of the combined organic and inorganic data set indicated that no significant differences existed between the concentrations of organic ions at the two sites; however, samples containing visible sediments had significantly greater concentrations than samples without sediments. Maximum contributions of the organic acids to precipitation-free acidity, calculated by assuming that the only sources of the measured formate and acetate were their respective acid forms, averaged 18.6% for samples with a pH ⩽ 5.0. Formate and acetate concentrations were highly correlated. Correlations between organic and inorganic ions were weak; NH⁺₄ and Ca²⁺ generally exhibited the highest, though still weak, correlations. The study emphasizes the need for further, longer-term investigations to determine the role of low molecular weight organic compounds in precipitation chemistry.