Comprehensive testing of indoor ventilation in underground transit hubs and microclimate in adjacent sunken plazas

Transit-Oriented Developments (TODs) are widely adopted as a sustainable strategy in the rapidly urbanising world. Underground transit hubs and sunken plazas, as key components of TOD communities, significantly influence the health and comfort of pedestrians, as well as energy consumption, through the modulation of indoor and outdoor ventilation conditions. This study conducted field tests to comprehensively investigate the thermal environment, humid conditions, ventilation conditions, and air quality within these areas. The main findings include: Sunken plazas demonstrate enhanced stability in temperature and humidity fluctuations relative to their aboveground counterparts. The sunken structure contributes to wind speed attenuation, with a more pronounced reduction observed at the entrance and exit of underground transit hubs compared to the central area of the sunken plazas. The difference in temperature between indoor and outdoor environments is a key factor influencing the overall airflow direction and ventilation performance, subsequently affecting the energy consumption of mechanical ventilation systems. The concentration and distribution of particulate matter are influenced by airflow patterns and wind speed, showing an increasing gradient from aboveground spaces to indoor crowded areas. The results provide scientific evidence and practical guidance for enhancing ventilation performance and air quality in sustainable urban design.