A citywide spatiotemporal perspective of particulate matter concentration on underground subway platforms

Abstract

21 Indoor air quality (IAQ) in semi-enclosed subway environments poses critical public health 22 concerns. This study investigates IAQ in Shanghai's subway system through year-round 23 monitoring of PM2.5 and PM10 across representative stations. Particulate concentrations were 24 markedly higher indoors, peaking during winter weekday morning rush hours, with 25 indoor/outdoor ratios exceeding unity. An interpretable machine learning model was developed 26 to elucidate key factors affecting IAQ, identifying platform screen door design and train 27 frequency as dominant influences. By integrating the model with network-wide operational data 28 and passenger boarding records, we quantified city-scale particulate levels and commuter 29 exposure. Further analysis incorporating point-of-interest data revealed that stations near 30 residential zones exhibited the highest exposure, while commercial density intensified pollution. 31 These findings provide a system-level assessment of particulate exposure within urban rail 32 transit and underscore the need for targeted ventilation and operational strategies to enhance 33 IAQ and safeguard commuter health. 34 35