A new study has provided a comprehensive, city-wide map of air pollution exposure within Shanghai’s subway system, identifying platform design and train schedules as critical levers for improving commuter health.
The research found that particulate matter concentrations on underground platforms consistently exceed outdoor levels, with exposure peaking in unexpected patterns.
Conducted through year-round monitoring of PM2.5 and PM10 at key stations, the study found indoor pollution levels were highest during winter weekday mornings.
The research employed an interpretable machine learning model which transformed the model from a simple forecasting tool into a diagnostic tool that allowed the team to make concrete, evidence-based policy suggestions.
Platform screen door (PSD) design emerged as the most significant influencer, with stations featuring full-height barriers showing markedly lower PM levels than those with older, half-height designs.
Train arrival frequency was the second key factor, as more frequent service increases mechanical wear-and-tear pollution from brakes and wheels, which can linger in the semi-enclosed environment.
The study states: ‘The findings are clear. A lower subway PM level can be achieved with the isolation between the train track and passengers on the platform using full PSDs.’
A significant revelation was that exposure risk does not necessarily align with peak pollution concentrations during the morning and evening rush hours. Often, overall commuter exposure can be highest during midday non-peak hours due to longer waiting times between less-frequent trains.
The analysis also overlaid pollution data with urban ‘points of interest’, revealing that stations near dense residential zones presented the highest exposure burden for communities. Meanwhile, pollution concentrations were most intense around commercial districts, but the shorter dwell times of shoppers moderated overall exposure risk there.
The team believe their insights form a blueprint for transit authorities, suggesting they should prioritise the retrofit of aging stations with full-height platform screen doors and optimise HVAC system schedules to allow for those midday periods, to mitigate prolonged exposure. It also calls for tailored strategies for stations serving vulnerable areas near hospitals and schools.
The authors conclude that ‘future improvements should be function-specific’, emphasising that protecting the health of subway commuters requires infrastructure upgrades based on precise, station-level data on both pollution sources and passenger patterns.
The full research can be read here
Photo: Touann Gatouillat Vergos
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