Error analysis applied to indirect methods for precipitation acidity

The historical increase in the acidity of precipitation in northern Europe has been monitored by measurements of pH and titrations of acidity. Indirect methods such as conductivity and balances as well as chemical source models have been used to confirm the measured . In the absence of historical records of direct measurements of acidity in precipitation in United States, indirect methods have been applied to available data on the composition of to quantify the acidity. Unfortunately, the indirect methods are sensitive to small errors certain pH regions. The effects of random errors in major ion concentrations as well as the errors due to the exclusion of trace metal and organic ions are shown to be largest pH 5.6 in the charge balance and chemical source strength calculations and largest pH 6.1 for the conductivity balance method. Estimates of the uncertainty in historical values of precipitation ion concentrations are used to calculate upper and lower bounds on acidity of rainwater in the United States before 1970. The trend of increasing acidity of in the northeastern United States is still evident after applying error analysis.