Set-up of a protocol for the assessment of indoor air quality towards the protection of works of art.

The effects of time and environmental conditions are well-known to be an issue with respect to works of art and historical buildings. Indeed, materials exposed both to outdoor and indoor environments are naturally subject to degradation over time. However, the importance of developing new methods to address the degradation of culturally significant objects is expected to grow in the future due to environmental causes. Fading, darkening, yellowing, and turning colour are only some of the better-known chemical degradation processes – induced or catalysed by environmental conditions - that affect works of art and architecture. Moreover, complex and multi-layered artistic works such as paintings, frescos and wooden carvings, which are made of a mixture of organic and inorganic substances, interact both with each other and the surrounding environment. In this research, the microclimatic conditions (temperature, relative humidity, and illuminance) and some air quality parameters such as particulate matter (PM) and pollutants (NO2 and BTEX) inside the Santuario della Beata Vergine dei Miracoli in Saronno (VA) were evaluated and monitored; this had the main purpose of determining whether the environmental requirements with regard to the health of the visitors and the conservation of the works of art present inside the building were adequate. In fact, in the interior part of this historical building a beautiful fresco cycle painted by one of the masters of the Renaissance, Bernardino Luini, is displayed together with other important and valuable frescoes, paintings and wooden statues. For this reason, dataloggers for temperature, relative humidity, and illuminance measurements, an optical particle counter (OPC) for PM determination and some diffusive passive samplers to quantify NO2 and BTEX concentrations were employed. The monitoring was performed at different locations in the Sanctuary, and lasted for several months, including important religious events like Easter Week. Furthermore, the outdoor parameters were evaluated and compared with the indoor ones to find possible correlations. Also, the characterisation of the colour palette and products of degradation on one the Luini frescoes was carried out through several non-invasive and portable spectroscopic and imaging techniques like hyperspectral imaging, Raman, FTIR and XRF spectroscopies, and colourimetry, with the main purpose of discovering the conservation state of the artwork and possible relationships between the products from degradation and the pollutants in the indoor environment.