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A detailed picture is presented of the internal consistency of the data generated by a typical acid rain monitoring system. Three independent techniques may be applied in the assessment of rainwater acidity: pH measurement, titration, and charge balance. Each is described. On the assumption that one solution can have only one acidity value, the three techniques present an excellent test for data consistency. Typical results from two extensive monitoring systems are shown.
The difficulties inherent in the titration technique are: agreement on protocol, reagent impurities, carbon dioxide interference, and weak acid end points. It will be shown that the titration technique is to be recommended in a very limited number of cases. The pH measurement technique is recommended provided it is understood that accuracy no worse than ±0.2 of a pH unit is acceptable. Methods of minimizing error are discussed. The charge balance method presumes the measurement of eight ions, minimum. Error sums and ultimate accuracy are described. Methodology recommendations are made. Practical results of analyses of real samples collected and analyzed by very inexperienced personnel under “adequate” supervision are shown.
rainwater analysis, titration curves, pH measurement, charge balance, quality control
Professor of chemistry, College of William and Mary, Williamsburg, Va.