New model for the sulfation of marble by dry deposition Sheltered marble-the indicator of air pollution by sulfur dioxide

This paper was concerned with evaluating the effect of dry deposition on deterioration of marble. Two types of marble were exposed to atmospheric environment with a rain shelter at four exposure sites in the south of Vietnam for 3-month, 1-year and 2-year periods from July 2001 to September 2003. X-ray diffraction (XRD) and X-ray fluorescent (XRF) methods were applied to study the products of marble deterioration. Ion chromatography was used to analyze dry depositions on marble. The main product of marble deterioration was gypsum (CaSO4·2H2O). The amount of sulfate ions deposited on marble was found to be proportional to SO2 concentration in the air, relative humidity and duration of the exposure. In addition, sulfation of marble caused by SO2 at a relative humidity lower than 70% is almost half of that at relative humidity higher than 70%. Moreover, marble consisting of calcite (CaCO3) was more sensitive to SO2 than marble consisting of dolomite (CaCO3 and MgCO3). A good relation between the amount of sulfate ions deposited on marble and SO2 concentration in the air suggested that marble could serve as an indicator for atmospheric pollution by SO2.