Albedo and thermal behavior of aged urban surfaces: Evidence from in situ measurements

Surface albedo is a key parameter controlling the radiative and thermal behavior of urban environments, directly influencing surface heating, near-surface air temperatures, and the urban heat island (UHI) effect. This study presents a field-based investigation of the albedo and thermal response of common urban ground and roof surfaces under real outdoor conditions in the University Campus of Patras, Greece. In situ albedo measurements were conducted using a dual-pyranometer for a representative set of aged and naturally weathered urban materials, including asphalt pavements, concrete surfaces, natural stone pavements, gravel and membrane roof coverings, vegetated ground surfaces during winter period, while surface temperatures were measured during a warm day in spring, using infrared thermography to assess the thermal implications of albedo variations. The results reveal important variability in albedo among urban materials. Mineral surfaces presented values ranging from 0.24 (aged asphalt) to 0.38 (marble), while vegetated surfaces showed lower reflectance (0.21-0.22) but distinct thermal behavior due to evapotranspiration. Higher-albedo materials consistently had lower surface temperature rise compared to darker surfaces, with differences reaching up to 10°C under peak solar radiation. A strong linear correlation (R 2 = 0.79) was also observed between absorbed solar energy and surface temperature increase, confirming the dominant role of albedo in controlling daytime surface heating. • Field-based evaluation of radiative–thermal behavior of urban materials • Higher-albedo pavements exhibit reduced midday surface heating • Nonlinear albedo–temperature relationship confirmed under identical exposure conditions • Vegetation stays cooler due to evapotranspiration despite low albedo