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Measured Particulate Matter Concentrations in New York City’s Subway System Suggest Exceedance of U.S. Environmental Protection

Fall 2021

Objective

To assess particulate matter (PM2.5) concentrations in NYC’s subway system using low-cost air sensors and determine whether they exceed EPA standards, with a focus on exposure risks for student commuters.

Methods

Devices Used:

  • PurpleAir PA-II-SD: Low-cost laser particle counter.
  • UPAS: Gravimetric filter-based sampler used for calibration.
  • Temptop M2000C: Nephelometer for real-time PM and CO₂ data.

Data Collection:

  • 25+ subway ride events.
  • Locations: Manhattan, Staten Island, Brooklyn, Queens.
  • Two strategies: (a) extended station sampling, (b) full commute sampling.
  • Calibration done via UPAS filters and outdoor reference stations.

Key Sites

  • Subway lines: 1, F, L, 7, SIR, W, etc.
  • Stations near schools: WHEELS (Manhattan), Curtis HS (Staten Island), West End Secondary.

Key Findings

PM2.5 Concentrations:

  • Average subway PM2.5: ~105 µg/m³
  • NYC outdoor average: ~6.55 µg/m³
  • EPA 24-hour standard: 35 µg/m³

Worst Stations:

  • 2nd Ave (F line): 407.88 µg/m³
  • Lexington Ave-63rd: 113.19 µg/m³

Best Air Quality:

  • SIR and W trains (mostly aboveground): < EPA thresholds

Commuter Exposure:

  • 2-hour daily commute: 19% above daily EPA threshold
  • MTA workers (8 hrs underground): 246% above threshold

Train Car Behavior:

  • PM drops during transit, rises at stops due to door opening

Health Implications

  • PM2.5 linked to respiratory and cardiovascular disease, especially in youth and elderly.
  • Underground PM contains metals (Fe, Mn, Cr) more harmful than typical urban PM.
  • Subway exposure could pose significant health risks over time.

Limitations

  • Only 4 PurpleAir sensors available.
  • Temporal and spatial coverage limited.
  • Lack of full chemical characterization of PM2.5.
  • Calibration methods varied slightly for aboveground vs underground data.

Recommendations

  • Install a network of calibrated low-cost air quality sensors across the subway system.
  • Conduct long-term air quality monitoring and integrate findings into public health alerts.
  • Focus on environmental justice, identifying communities disproportionately affected by subway-related pollution.

Future Directions

  • Expand data collection to all subway lines and times of day.
  • Apply similar monitoring in other indoor public spaces (e.g. schools, buses).
  • Use findings to inform ventilation upgrades and policy changes in subway systems.

Acknowledgements

  • NYC Outward Bound Schools
  • NYC Department of Education
  • Faculty Advisor: Dr. Benjamin Bostick
  • Capstone Team: Greg Hopper, Noah Portman, Joseph Galbiati

Full report available here.