Atmospheric damage to calcareous stones: Comparison and reconciliation of recent experimental findings

A compilation of published data on the rates of mass loss from calcareous (carbonate) stones is presented Data from nine of these field exposure experiments are then used in statistical analyses to postulate cause-and-effect relationships with environmental variables, i.e. damage functions, based on a theoretical framework. The metric recommended to estimate rates of damage is ‘material lost per meter of precipitation’, as affected by three mechanisms: calcite dissolution in “clean” rain (pH = 5.6), additional dissolution due to acidic precipitation, and loss by conversion to soluble salts as a result of dry deposition of SO₂ or other acidic species. The working hypothesis for dry deposition of SO₂ is that rain is needed to maintain the activity of dry deposition sites, by washing away the gypsum which has been formed. Although consistency is shown for damage functions derived from theory and from several different experimental programs, some outliers are also shown, indicating the importance of specific stone properties, physical arrangements, and experimental protocols. In addition, these damage functions are not capable of predicting catastrophic damage to stone resulting from exfoliation of sulfate crusts that have accumulated over time.