Carbonaceous particles and stone damage in a laboratory exposure system

The interaction between carbonaceous particles and stones used in historic buildings and monuments was investigated in a laboratory exposure system. Simulation experiments were carried out in a flow chamber where temperature, relative humidity, and SO2 concentration were controlled. Samples of carbonate stones (Carrara marble, Travertine, and Trani stone) were exposed for 150 days in air with 3 ppm of SO2 concentration at 25 degrees C and 95% relative humidity. The stone specimens were coated with three types of carbonaceous particles (P1, P2, and P3) collected at the emission points of three oil-fueled combustion sources: one centralized domestic heating plant and two electricity generating stations. For comparison, particles of activated carbon and graphite were also deposited on the stone samples. After exposure, samples were analyzed by X ray diffraction and infrared spectroscopy to identify the main chemical species, by ion chromatography to quantify SO4= and SO3= concentrations, and also by scanning electron microscope. The results show that the amount of SO4= formed increases in the presence of carbonaceous particles and is related to their heavy metal content.