The Oceanus statue of the Fontana di Trevi (Rome): The analysis of black crust as a tool to investigate the urban air pollution and its impact on the stone degradation

This paper deals with the analysis of black crust coming from the statue of Oceanus belonging to the Fontana diTrevi (Rome). This monument is undoubtedly one of the main touristic attractions of Rome. During the restorationheld between 2014 and 2015, somediagnostic analyses had been carried out. It has been highlighted that thesheltered surfaces suffer the formation of black crust, especially on the marble statues. The possibility to samplethose degradation products, together with the unaltered substrate, represented an excellent opportunity to characterizethe marble itself, to assess the impact of the urban air pollution on the stone material, and to detect thepollutant on a precise timescale. In fact, it is known that the previous restoration of the fountain had been carriedout between 1989 and 1991 then, information about the air pollution over the last 25 years can be highlighted,because it has been proved that black crusts act as passive samplers of pollution. In order to fully characterizethose samples, several techniques were used, including optical and scanning electron microscopy, X-ray diffraction,laser ablation inductively coupled plasma mass spectrometry, infrared spectroscopy and ion chromatography.Furthermore, a newmethodology based on CHN (Carbon, Hydrogen, Nitrogen) analysis has been developedfor the quantification of the two main constituents of the carbonaceous fraction present in the black crusts, i.e. OC(organic carbon) and EC (elemental carbon).