Influence of subway entrance layout on indoor and outdoor environments in street canyons with different geometric form

With increasing subway use and in-depth research on pollution associated with subway systems, human exposure to pollutants in metros has received widespread attention. Studies on street pollution, flow fields, and relationships between external pollution and subway entrances have not been fully explored. This study focused on street canyons that contain subway entrances to determine the effects of different street canyon morphologies and subway entrance locations on the pollutants present in the environment. After verifying the feasibility of the software through a neighborhood experiment that applied the ENVI-met model for pollutant dispersion in the canyon, we analyzed the fine particle distribution and wind environment using variable models for streets with different subway entrance locations. The results showed that (1) inside subway entrances, pollution was more severe on the windward than the leeward side; (2) descending street canyon morphology was the most detrimental to air quality inside subway entrances; (3) street canyons rising along the wind direction were most favorable for air quality at pedestrian height inside the neighborhood; (4) at subway entrances located in the street extension direction, the leeward subway entrances had higher particulate matter concentrations at the center of the building, whereas windward subway entrances exhibited higher concentrations near the edge of the building. This study suggested that indoor exposure to pollutants in the subway is sensitive to the layout of entrances in street canyons with different geometries and provides recommendations to improve the layout of subway entrances based on air quality.