Possible alteration of monuments caused by particles emitted into the atmosphere carrying strong primary acidity

We discuss the effects of the presence in the atmosphere of acidic ashes originating from the burning of oil heavy fractions and of the damage they could cause to monuments if deposited onto them. After quantifying its load of potentially strong acidity, we studied the effect of this particulate coming into contact with samples of two of the most common types of calcareous materials used in the building of monuments in atmospheric conditions characterized by relative humidity values of between 0 and 94%. Visual examination of the surfaces of the calcareous materials revealed substantial alteration even after brief periods of exposure in atmospheres with relative humidity values above 40%. The transformation of calcium carbonate into bihydrate calcium sulphate and the release of coloured metal ions, both promoted by the humidity absorbed from the atmosphere, were evidenced by SEM images and confirmed by WDS probe investigation and XRD examination of the altered layers of material.