A multi-analytical approach for the characterization of black crusts on the facade of an historical cathedral

This study focuses on the characterization of black crusts collected from the Monza cathedral located in the homonymous city (N Italy), a hot spot from the point of view of the atmospheric pollution. Black crusts and substrate marble specimens were analyzed by a multi-analytical approach including X-ray Diffraction (XRD), Fourier Transform-Infrared spectroscopy (FT-IR), Stereomicroscopy (SM), Polarized Light Microscopy (PLM), High Resolution Scanning Electron Microscopy coupled with Energy Dispersive X-ray spectroscopy (HRSEM-EDX) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP/MS). The characterization of the carbon fraction (organic carbon, OC, and elemental carbon, EC) was performed using a new approach based on the use of Carbon Hydrogen Nitrogen (CHN) analysis and Thermogravimetric Analysis (TGA). The integrated approach allowed the identification of the pollution sources responsible for black crusts forming process. The precise identification of the main substances responsible for the surface degradation phenomena, in particular those leading to the blackening and disintegration of the carbonate substrates, is essential for the definition of conservative intervention and maintenance strategies, as well as for the development of emission reduction policies on a local scale.