Correlation between aerosols, deposits and weathering crusts on ancient marbles

The structure and physicochemical characteristics of weathered surfaces of marble in industrial environments can be attributed to the interconnected evolution of the processes taking place at the atmospheric environment--marble interface. The present work is an attempt to correlate the aerosols of a heavily polluted atmosphere with the different weathering patterns observed on marble surfaces. Energy Dispersive X-Ray Fluorescence, X-Ray Diffraction, Porosimetry, Atomic Absorption, Atomic Emission Spectrometry, Ion Chromatography, Optical Microscopy and Scanning Electron Microscopy results were used together in principal component and discriminant analysis. These analyses were performed on forty six samples of aerosols and eighteen samples of crusts. Other parameters like orientation of the weathered surface, exposure to rainfall, presence of recrystalised calcite and gypsum were also used. The samples were collected from the archaeological site of the Sanctuary of Demeter, located near Eleusis (west of Athens, Greece), where a great number of industries (mainly metallurgical and chemical) cause several environmental problems. The results provide invaluable information on the nature of marble surface decay. The elements determining the chemical composition of the coarse airborne particles are Ca, Si, S, Br and Cl. The presence of gypsum is strongly related to black crusts or loose deposits. Y, Mn and rain exposure, are correlated with each other and related to black-gray crusts. Ca and Sr are correlated with washed-out surfaces. Finally discriminant analysis is proved to be a powerful tool in prediction of the type of decay that will be occur on a marble surface, given the composition and type of the polluted atmosphere.