An evaluation of uncertainty associated with aluminum equilibrium calculations

There is considerable concern over the impact of elevated concentrations of A1 in drainage waters acidified by atmospheric deposition. Computer models developed to evaluate the acidification of surface waters generally rely on thermodynamic calculations to predict the concentration and speciation of A1. We present a simple chemical equilibrium model that can be used to evaluate the chemistry of acidic waters which favorably agrees with results obtained from more comprehensive models. Additionally, we evaluate the effect of error in thermodynamic data on calculations of A1 chemistry by Monte Carlo methods. Variations in model output due to uncertainty in the determination of equilibrium constants were small. However, there is considerable variation within the literature of thermodynamic data for a given reaction. This “literature error” results in as much as 100% variation in the concentration of A1 complexes.