Pollution effects on typical Florentine lithotypes: a multidisciplinary approach

Mobile combustion sources are known to be one of the main causes of damage to cultural heritage located in urban areas. Soiling and blackening affecting buildings and architectural surfaces are principally due to the deposition and accumulation of the carbon fractions associated with particles emitted by combustion processes. Chemical weathering, including formation of new products and dissolution/re-crystallization phenomena, is also occurring, depending on both the environmental conditions to which the heritage is exposed and the intrinsic (chemical, physic-chemical, petrographic) characteristics of the materials themselves. Several efforts have been made to better understand the deterioration phenomena caused by the impact of pollution (gas and aerosol) on cultural heritage and to improve monitoring of their surrounding environments. The knowledge gained could be a valuable tool for initiating preventive conservation strategies and for predicting the durability of restoration interventions. However, at present there still is lack of knowledge about the quantitative correlation between the concentrations of specifi c atmospheric pollutants and their effect in terms of damage (i.e. dose-response functions). Therefore, in order to assess the effects of mobile combustion sources, an historical building in the centre of Florence, Italy, was selected for a 24 month exposure test (started in September, 2012) using three typical Florentine building lithotypes: Carrara marble, Pietraforte and Pietra Serena. The principal focus of the exposure test is to characterise the different effects, including aesthetical impact, of soluble and carbon fractions of particulate matter on the selected building materials. The samples of the lithotypes are positioned in a loggia at the San Marco Museum and overlooking a heavy vehicular traffi c street. Ion chromatography analyses, chemicalthermal methodology for carbon speciation, and UV-Vis-NIR and Mid IR refl ectance spectroscopic investigations are planned to be performed at six-month intervals on the surface deposit of the exposed lithotypes. The ions and carbon fractions concentration data will be correlated to the surface blackening and evaluated in terms of both colorimetric coordinates and the refl ectance patterns in UV-Vis-NIR- Mid IR spectral ranges. Preliminary results will be presented and discussed.