Promoting the design of future urban metro systems to improve air pollution: Based on metal element pollution in Chinese metro system

Abstract

Metro system metal element pollution and its human hazards have gained widespread attention. Using the Chinese metro as representative of a modern urban metro system, we investigated pollution levels, sources, and their health effects, to provide a basis for designing future healthy, sustainable urban metro environments. Through searching and analyzing previous studies on metal elements in the Chinese metro system, we showed that tunnels are the most contaminated areas for metal elements due to mechanical wear, while platforms, carriages, and halls are mainly affected by airflow diffusion. Using the UNEP-SETAC toxicity (USEtox) model to calculate health impacts, we determined that metal elements caused approximately 700 deaths per 1 million people annually. According to the US Environmental Protection Agency (US EPA) health risk model, health risks were evaluated from respiratory exposure for child and adult passengers, drivers, station attendants, and security checkers. Total incremental lifetime cancer risk (TILCR) for all populations was higher than 10−4, indicating a high carcinogenic risk. Finally, based on international studies, we propose corresponding strategies to improve metro system sustainability.