Erratic cultural heritage as a monitoring tool for environmental and anthropic impact in the city of Venice

Air quality and climate have relevant impacts on the exposed cultural heritage and architectural surfaces, increasing degradation phenomena such as erosion, detachments, and biological growth. In Venice the climatic effects are further enhanced by the presence of lagoon water since the soluble salts therein are responsible for significant further degradation processes in materials [1], [2], [3], [4], [5] . The huge tourism increase is bringing, in its turn, a transformation of the city, in terms of values and authenticity, but also in terms of enhanced material degradation. Warnings regarding the threats of climate change and mass tourism to cultural heritage in Venice came recently also from the World Heritage Centre of UNESCO, which stated that “The effects of the continuing deterioration due to human intervention, including continuing development, the impacts of climate change and mass tourism threaten to cause irreversible changes to the outstanding universal value of the property” [6], [7], [8]. Monitoring is one of the most important instruments to preserve cultural heritage, avoid expensive intervention for its maintenance and restoration and develop cost-effective strategies However, monitoring generally focuses on single case study with their own specificity, the results of which are often difficult to be applied to other assets. Even prediction models do not always consider all the variables involved in the degradation processes observed on the manufacts [3], [4], [9], [10], [11]. This project aims to use “minor” cultural heritage spread throughout the historic centre of Venice to evaluate the decay evolution on an urban scale considering the intrinsic characteristics of the materials and the surrounding environment. In the context of PNRR CREST (Cultural Resources for Sustainable Tourism) project and thank to the collaboration with the volunteers of the Nucleo Tutela Beni Culturali of Venice Civil Protection, we accessed a repository of more than 900 assets (sculptures, decorative and architectural elements, religious shrines, etc.) spread only over the Cannaregio Sestiere. These artworks, even if not belonging to the most recognized ones in the city, are important elements of Venice's heritage, since they build a part of every-day life and identity of the citizens. Moreover, beside their socio-cultural meaning, they Book of Abstracts: ChemCH2024 7th International Congress Chemistry for Cultural Heritage Bratislava, July 2-5, 2024 represent an invaluable asset which tells the city’s transformations over time related to environmental factors and voluntary or involuntary anthropogenic activities. Many photographs of these so called “erratic heritage”, have been collected. The material gathered comprises recent and archive photographs which belong to the repository of the Civil Protection, to several private and public archives or taken from books. For several heritage surveyed it was possible to retrieve archive photographs older than thirty years and visually evaluate the physical transformation upon time, since they were covering a prolonged time span. To assess the presence of any recurrent transformation patterns and the relationship between the observed modification and the surrounding environment, several parameters were considered for each heritage: the material, the position with respect to the canals (nearby or far away from it) and to the ground level and the specific exposure of the heritage (exposed to rains or sheltered). First results show similar decay evolution for exposed (not sheltered) heritage, regardless of whether they are facing the canal or located on intern calli or courts. An overall decrease of gypsum black crusts is observed for several of the considered heritage, reflecting the reduced presence of SO2 as degradation factor with respect to the past. Black crusts decrease and limited impact of SO2 over stone material is confirmed by in situ Raman spectroscopy analyses, while run-off impact caused a loss of legibility of the single artifact and it is here evaluated according to a scale of value from 1 to 3 (1=still readable, 2=partial loss, 3=unreadable) [2], [12], [13], [14]. In addition, religious shrines represent an interesting example of how the presence of people influences the conservation state of these heritage, they are usually at head height, and they are among the most deteriorated ones due to the rubbing action of the faithful. In conclusion, the aim of this work is the development of a methodology to read at the environmental impact observed on the surface of these heritage through non-invasive monitoring systems (validated with diagnostic instruments) applicable on a large scale at urban level. Data acquired from this study will allow the construction of a detailed map of the most affected areas of the city. The heritage located in these areas should be then monitored with more attention above all with respect to the most important ones sited in their surrounding (i.e. churches, buildings, statues).