How Does Air Quality in a Philly Subway Station Compare to the Outdoors?

A study by Villanova University researchers Kabindra Shakya and Aimee Eggler reveals that air quality in downtown Philadelphia’s City Hall subway station is significantly worse than the street-level sidewalks in the same location.

As the authors explain in an article in The Conversation, “We focused on this station because our previous study found it to have the highest levels of particulate matter among 12 Philly subway stations we measured on the busy Market-Frankford or Broad Street lines.” They found 10 times more black carbon — also known as soot — in the station than outdoors, generated by the subway system itself.

“Limited access to outside air, the frequency of trains, a large number of passengers and its location in the heart of Center City may be some of the reasons for the high concentrations of particulate matter at the 15th Street station,” the authors add.

The city could improve air quality in the subway by replacing aging equipment and rails, adding platform screen doors, and increasing ventilation. However, the authors stress that they are not recommending people avoid the subway. “Air pollution levels are highly variable across stations and over time, and commuters spend relatively short periods of time inside subway stations.”