Genesis of black crusts on building stones from three Italian cities: relations with environmental pollution.

The deposition of atmospheric pollutants on stones is one ofthe most important causes of the deterioration which affects thefacades of buildings and monuments (AMOROSO & FASSINA1983; DEL MONTE et alii 1981; TURKINGTON et alii 1997; ZAPPIAet alii 1998).In polluted environments, black crusts usually develop oncalcareous rocks.In this contribution, we characterise some black crust samplescollected from monuments and buildings of three Italian cities:Milan, Rome and Catania. Specifically, the examined specimensinclude:1) three samples from the cloister of San Cosimato convent inRome, now the Regina Margherita Hospital;2) two samples from the sculpture of an angel located inPessano con Bornago, a small industrial centre near Milan;3) seven samples from monuments and buildings variouslydistributed in the Catania city centre.Both substrate and black crust were studied for each samplethrough the synergic utilization of traditional analytical methods(polarizing optical microscopy, SEM-EDS and FT-IR), incombination with an innovative technique, i.e. laser ablationinductively coupled mass spectrometry (LA-ICP-MS).The aim of this study was to evaluate the degree of chemicalcontamination of examined stones through the determination oftrace elements variability from unaltered substrate to black crust.In addition, relations between concentrations of pollutingelements in black crusts and environmental conditions were alsoinvestigated, thus allowing to understand the role of the differentsources of pollution.A complete discussion of the data presented here is reportedin two papers recently published by the authors (BARCA et alii2010, 2011).