Assessment of Urban Heat Mitigation Strategies to Improve Outdoor Thermal Comfort Regarding Carbon Dioxide Concentration in Tehran Metropolis

Two leading factors that deteriorate environmental conditions and well-being are urban heat island (UHI) as a micro-climatic phenomenon and carbon dioxide (CO2) concentration as the most critical greenhouse gasses. The aim of this study is to enhance outdoor thermal comfort (OTC), UHI, and CO2 concentration in a polluted and heated area with a high potential for promoting a sustainable culture. For this purpose, several sustainable solutions were evaluated, including cool roofs (CR), green roofs (GR), cool pavements (CP), vegetation greenness (VG), and total alternative (TA). Initially, the strategies were investigated individually, and later collectively in one part of the study area, and then expanded to the whole site for more assurance. The research results were extracted by ENVI-met (4.5.6) and then field measurements and another software's result, namely Element, Rhino and Grasshopper. According to the results, the VG scenario is the most effective strategy to improve OTC indices and CO2 concentration. Moreover, the CP scenario, with permeability, has the most crucial role in UHI mitigation, especially the nocturnal one; it is important to note that no study in the Middle East has been able to improve nocturnal and diurnal UHI simultaneously. Field measurements and another software's result validate our findings. Studied thermal comfort indices have the highest correlation with mean radiant temperature, followed by air temperature and CO2 concentration. Thus, this study provides a new perspective to appraise the effectiveness of CO2 concentration as an essential factor in this field and practicable solutions for designers.