Aerosol sources in subway environments.

Area of Science:

• Environmental Science
• Atmospheric Chemistry
• Public Health

Background:

• Subway environments have high particulate matter (PM) concentrations.
• Understanding aerosol sources is crucial for improving air quality in public transport.
• Millions globally rely on rail subway systems daily.

Purpose of the Study:

• To identify and quantify aerosol source contributions in the Barcelona metro system.
• To analyze the chemical composition of PM2.5 and subway components.
• To assess the impact of station type and operational activity on air quality.

Main Methods:

• Conducted an aerosol monitoring campaign in 11 Barcelona subway stations.
• Collected and chemically analyzed PM2.5 samples for elements, ions, and carbon.
• Determined the chemical composition of subway components (brakes, rails, pantographs).
• Applied receptor modeling (Positive Matrix Factorization) to identify emission sources.

Main Results:

• Mean PM2.5 concentrations ranged from 26 to 86 µg/m³.
• Subway PM2.5 was dominated by Fe2O3 and carbonaceous matter.
• Newer stations with Platform Screen Doors (PSD) showed lower PM2.5 concentrations.
• Ten sources were identified, including five subway-specific ones (e.g., RailWheel, Brake).
• Subway sources contributed significantly (21-91%) to bulk PM2.5.
• Weekend activity reduced subway-specific source contributions.
• Health-related elements were primarily attributed to subway sources (>60%).

Conclusions:

• Aerosol composition and source contributions vary significantly across subway stations and lines.
• Platform Screen Doors (PSD) can reduce PM2.5 concentrations.
• Receptor modeling successfully identified key subway-specific emission sources.
• Reducing subway activity, especially on weekends, lowers PM2.5 and associated source contributions.
• Subway-specific sources are major contributors to health-related elements in subway air.