The unacceptable level of veiling and dust in heritage buildings: The case study of the Angelica Library in Rome, Italy

The presence of dust and its accumulation on surfaces represents a challenge to maintaining clean indoor environments. In the case of heritage buildings, such as museums and libraries, dust deposition can lead to both aesthetic and physical damage. Starting from the scientific literature on dust and heritage buildings, this research aims to provide a theoretical framework for the phenomenon of dust soiling and proposes an empirical method to estimate dust deposition, based on Stokes’ law and indoor monitoring of particulate matter. The main objective is to develop a data-driven tool for risk-assessment associated with atmospheric particulate matter (PM) deposition and maintenance scheduling, through a combination of experimental measurements and theoretical modelling. The study involves collecting environmental data, assessing indoor thermal stability, estimating deposition velocity and evaluating the loss of surface reflectance. Based on these analyses, two indicators for dust accumulation are defined: the Unacceptable Visual Limit (UVL), a risk index representing the threshold of unacceptable veiling derived from reflectance measurements, and the Dusting Frequency (DF). These indicators are then applied to the case study of the Angelica Library in Rome, Italy, using a low-cost platform for measuring microclimate and PM2.5 concentrations. The case study represents a low-pollution baseline scenario with low deposition rates, leading to a recommended dusting frequency of approximately 230 days for a UVL of 0.2%. The results demonstrate the practical utility of the proposed methodology in guiding low-cost, data-driven dust management strategies in heritage buildings.