“…In fact, weathering, chemical and physical stress, organic and inorganic matter deposition, and microbial growth over time, or "aging", affect the optical and radiative response of building envelope materials [10,11], reducing the cooling savings offered by cool materials [7,12]. The effects of aging on the albedo of building materials are consistently documented by outdoor exposure campaigns performed in the US [13,14], Europe [7,12,15], South America [16,17], Japan [18,19], and China [20,21]. The main ingredients of soiling are approximately the same in all urban contexts [15], with a dominant role of black carbon [14].…”