A Physical-Chemical Interpretation of Mean and Extreme Values in Acid Precipitation

A physical-chemical model is used for the interpretation of mean and extreme concentrations in acid precipitation. Chemical concentration frequency distributions tend to be skewed, as a result of the log-normal distributions for advective transport processes and skewed distributions for precipitation intensity and volume. The mean concentration of a conservative constituent is independent of sampling interval, but the sampling strategy influences the spread of the distribution. Little difference is noted for the distributions of samples taken by storm and by week. The use of (H** plus ) (a non-conservative quantity) instead of net acidity or alkalinity (conservative quantities) results in significantly lower calculated mean pH values for the West.