Natural and anthropogenic sources of total suspended particulate and their contribution to the formation of black crusts on building stone materials of Catania (Sicily)

Blackening and disaggregation of exposedsurfaces of stone monuments are well-known effects ofstone decay taking place in polluted urban environments allover the world. This paper aims to assess the contributionof natural and anthropogenic sources of total suspendedparticulate (TSP) causing permanent damage (black crusts)to the stone monuments of Catania (Sicily), one of the mostpopular ‘‘cities of art’’ of southern Italy. Atmosphericpollution of Catania, a typical Mediterranean coastal town,is mainly contributed by vehicle exhaust emissions ratherthan industrial ones. Episodically, the city also suffersgaseous and ash emissions (plumes) from the nearbyMount Etna volcano. Thus, to discriminate between naturaland anthropogenic contributions to stone decay on Cataniamonuments, black crusts and TSP were sampled within theurban area and subjected to specific analytical procedures(optical microscopy, X-ray powder diffraction, Fouriertransformed infrared spectroscopy, scanning electronmicroscopy equipped with energy dispersive spectrometry,ionic chromatography and dual inlet mass spectrometry).Mineralogical, chemical and isotopic characterization ofblack crusts and TSP provided new insights concerning thepartition of sulfate sources in this particular urban context.The influence of Mount Etna emissions on both TSP andblack crusts compositions was shown. Nevertheless, thekey role of anthropogenic sources in the total sulfate budget was confirmed, while sea spray and volcanicemissions were found to make subordinate contributions.Quantitative data useful for the identification of thethreshold pollution levels for preventive conservation ofCatania monuments were obtained.