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Architectural limestone surfaces are particularly susceptible to decay from natural and anthropogenic acidifying gases and particulates. This investigation evaluates environmental conditions, air quality, and decay patters on Istria stone surfaces of four palaces in Venice (Italy): Ca' Bembo, Ca' Bottacin, Ca' Foscari, Ca' Dolfin. Climate parameters and air quality indicators are used to discuss the atmospheric influence on limestone and to calculate the related theoretical recession rate. Graphic assessment, surface profiling, digital microscopy, infrared spectroscopy, and x-ray fluorescence are used to assess stone surface textures and degradation patterns associated with stone decay. The morphological analysis via surface profiling using silicon mould, digitization and statistical analysis of the roughness is proposed for the assessment of stone deterioration. In particular, the methodology is used for understanding stone morphological variations in relation to parameters such as sites, exposure (sheltered or exposed area), and location (overlooking a Canal or inner court).

In relation to increasing rain amount and intensity, decreasing SO2 and increasing NOx concentrations, theoretical limestone recession rate compatible with an urban environment (around 8 mu m/year) are calculated. The morphological analysis of the sites evidences the role of the stone original texture and finish, the facade location and the specific exposure on the formation of crusts or eroded area. Buildings not recently restored (Ca' Bottacin and Ca' Bembo) present thick dendritic crusts, in particular on court side and in sheltered positions. Ca' Foscari surfaces, subjected to cleaning intervention after 2000s, show thin grey crust only in sheltered areas, reflecting the reduced presence of SO2. Large eroded areas have been found on exposed surfaces in relation to the rain wash-out action and to high levels of NOx.