Effects of cool coatings on urban microclimate and outdoor thermal comfort: A CFD–CitySim pro coupled simulation study

• Coupled CitySim Pro–CFD model evaluates thermal effects of cool coating material. • Cool coating material applied based on building height and material envelope. • Radiative interactions from cool coatings shift urban air temperature patterns. • Cool coatings reduce air temperature but can worsen pedestrian thermal comfort. • Cooling coating strategies should be tailored by spatial traits and human activity. This study examines how cool coatings, which modify the radiative properties of building and ground surfaces, affect urban microclimate and pedestrian thermal comfort in a district with heterogeneous building heights. A computational fluid dynamics (CFD) model coupled with CitySim Pro explicitly resolved shortwave and longwave radiative exchanges. The framework was validated against field measurements, demonstrating high accuracy for surface/air temperatures and wind speed/direction in the control experiment (CNTL) using in-situ material properties. Sensitivity experiments revealed that high-rise facade coatings (BiGc, BiGj) reduced the coated facade surface temperature by 4.70–5.56℃, but increased temperatures on nearby low-rise facades and roofs by up to 6.03℃ and 4.06℃, respectively. In the combined case (BiGj), adding high-reflectance pavement mitigated the facade-induced ground warming observed in BiGc by ∼ 2℃. Ground-only coatings (BcGj) lowered pavement temperature by 1.71–2.24℃ while producing only minor thermal changes on surrounding buildings. Regarding air temperature, ground-only coatings produced marginal nighttime cooling and ∼ 0.5℃ daytime cooling, primarily over open spaces. Facade-involved scenarios achieved up to 2℃ daytime cooling near deep canyons but caused localized nocturnal warming of 0.3–2.0℃ in medium and shallow canyons. Universal Thermal Climate Index (UTCI) analysis at the Gwanghwamun Square showed ground-only coatings increased daytime UTCI by < 1℃ on average, whereas facade-involved treatments raised UTCI by up to 4.13℃ due to intensified mean radiant temperature. Overall, ground-centric coatings minimize comfort penalties, while facade treatments require strict radiative control. Prioritizing shaded ground applications in high-activity areas offers a practical balance between urban cooling and pedestrian well-being.