Effect of stone thickness on run-off water composition and derived damage functions in ambient exposure experiments

Field-exposure studies have been carried out to study the correlation between environmental conditions and limestone weathering, using analyses of the run-off rain water. Because no short-term correlations between environmental parameters (e.g. daily SO2 levels) and stone decay (e.t. concomitant Ca2+ release) have been observed until now for stone slabs with a “standard” thickness of 5 cm, stones of different thicknesses (1 and 5 cm) were exposed in parallel to check the influence of reaction product retention within the stones. It was expected that the thinner stone should retain relatively less. However, no significant differences in released ions were found. Consequently, the absence of correlations between atmospheric conditions and stone decay during short time intervals (e.g. 1 d) does not appear to be due to retention of ions in the stone. Also, it does not appear possible to correlate stone decay solely with the concentration of pollutants in the air, and other parameters have to be included. A damage function has been constructed to explain the Ca2+ loss for both stone thicknesses as a function of rain input and environmental conditions. For the limestone of 1 cm thickness, the decay can be predicted well.