Solar spectral reflectance of building envelope materials after natural exposure in Rome and Milano, and after accelerated aging

Material weathering, dirt deposition (mainly soot and organic matter) and microbial growth, collectively referred to as aging, modify the optical and radiative response of building envelopes. Long-term data about the initial and aged solar reflectance are available for roofing products exposed at three sites in the U.S. (Arizona, Florida, and Ohio). Based on this dataset, an accelerated weathering and soiling protocol was developed by the Lawrence Berkeley National Laboratory (LBNL) to mimic the spectral reflectance after three years of natural exposure. Herein, we present an extension of the accelerated aging protocol to reproduce in the laboratory the conditions in Italian urban areas (and, in general, in urban areas), by tuning the spraying duration and soiling composition. We compared the UV-Vis-NIR reflectance of naturally-aged samples (18 months in Rome and Milano) with that of samples exposed to accelerated weathering and soiling in the laboratory, achieving a good agreement between the spectral reflectance of the naturally-aged samples and of those aged with the accelerated protocol. The results herein presented relate to single-ply roofing membranes, terracotta tiles, and façades finishing coats. For very reflective membranes (initial solar reflectance greater than 0.80), after the first 18 months of natural exposure, we observe absolute losses of solar reflectance in average equal to 0.20 (maximum of 0.25), and the accelerated exposure is able to reproduce the UV-Vis-NIR spectra to within 0.02 for most of tested products.