Indoor Air Quality Assessment in Subway Systems
Summary
Subway systems are enclosed urban environments that expose millions of daily commuters and workers to complex aerosol mixtures. Confined architecture, train-induced mechanical abrasion, wheel–rail friction and brake wear generate metal-rich particulates that accumulate in tunnels and platforms. Semiquantitative and real-time measurements employing gravimetric sampling, optical particle counters and portable monitors reveal PM2.5 and PM10 concentrations often exceeding ambient levels by an order of magnitude. Chemical speciation identifies iron oxides, calcium, silicon and trace metals as dominant components. Ventilation design, platform screen doors and air-filtration systems have been implemented to mitigate pollutant levels; however, variability across networks reflects differences in line depth, train frequency and air-exchange rates. Interdisciplinary approaches linking particle provenance, indoor transport dynamics and health endpoints underpin efforts to optimise subterranean air quality and inform policy globally.
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Indoor Air Quality Assessment in Subway Systems publication trend
The graph below shows the total number of articles in indoor air quality assessment in subway systems across all publications each year (not limited to Nature Index journals).
Technical terms
Particulate Matter (PM2.5, PM10): Airborne particles classified by aerodynamic diameter, with PM2.5 referring to particles ≤2.5 µm and PM10 to particles ≤10 µm.
Confocal Microscopy: Optical imaging technique that generates three-dimensional reconstructions of particulate structures by combining multiple focal planes.
Scanning Electron Microscopy (SEM): High-resolution imaging method using electron beams to visualise surface morphology and perform elemental analysis via backscattered electrons or energy-dispersive X-ray spectroscopy.
Emission Factor: Quantitative metric expressing the mass of particulate emissions per unit of operational activity (e.g. g/km of rail travel).
Heart Rate Variability (HRV): Measure of variations in time intervals between heartbeats, reflecting autonomic nervous system regulation.
References
- 3D Imaging of Roadside and Underground Railway Particulate Matter Structures. Environmental Science & Technology Letters (2023).
- A pilot study of the cardiopulmonary effects in healthy volunteers after exposure to high levels of PM2.5 in a New York City subway station. Particle and Fibre Toxicology (2024).
- PM emissions from railways – Results of tests on a wheel-rail test bench. Transportation Research Part D Transport and Environment (2023).
- Environmental and Health Effects of Ventilation in Subway Stations: A Literature Review. International Journal of Environmental Research and Public Health (2020).
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