Impact of photonic properties of a new radiative cooling material on the urban heat island and the radiation balance

A photonic meta-concrete (PMC), a radiative cooling material based on conventional concrete, is under development. This material reflects solar radiation through its high albedo and emits heat as longwave radiation via the atmospheric window, achieving effective cooling. This study assesses the PMC's impact on the urban heat island (UHI) in Belgian cities using the COSMO-CLM regional climate model with the TERRA_URB urban surface parametrization, simulating a 5-day heatwave across Flanders with 1 km horizontal grid spacing. Additionally, the study estimates radiative forcing from PMC application through a radiation scheme and translates this into CO₂-equivalent emission reduction. The results indicate that PMC reduces the UHI in Brussels, lowering daily surface and nightly 2-m air temperatures by 9.6 °C and 2.7 °C respectively, due to the material high albedo. Scenarios with varying PMC coverage ratios show a non-linear relationship between coverage and temperature reduction, where lower coverage yields smaller cooling effects. Applying PMC to all urban roofs results in a radiative forcing reduction of 69.7 W/m 2 , equivalent to 22 kt of potential reduced greenhouse gas emissions. Although full PMC coverage on urban rooftops may be challenging, these findings underscore the material's potential for UHI mitigation, offering substantial cooling benefits and greenhouse gas reductions in large-scale applications. • Widespread PMC implementation lowers the urban 2 m temperature by 2.7 °C in Brussels. • Albedo identified as driving characteristic in reducing urban temperatures. • Non-linear relationship between temperature reduction and PMC coverage rate. • PMC application yields 69.7 W/m 2 radiative forcing or 22 kt reduced CO₂eq emissions.