A new study has revealed that the air quality inside Philadelphia’s subway stations is significantly worse than the air on the city’s streets. Researchers found that levels of harmful particulate matter, including black carbon (soot), are up to 10 times higher underground than above ground. This raises concerns about the health risks for commuters and subway workers. The study highlights the need for improved ventilation and better maintenance to reduce exposure to these pollutants. Air pollution is a major public health issue, and this investigation sheds light on a concerning problem in Philadelphia’s transit system.
Dangerous Particles Once Again At Seriously Unsafe Levels
The scientists — an environmental scientist and biochemist — made a state-of-the-art analysis of air quality at the 15th Street-City Hall subway station in Philadelphia. Inside the station, the levels of black carbon—a key ingredient in PM2.5—were higher by a factor of about 10 than they were above ground at street level.
The study also focused on the health effects of air pollution which includes black carbon or soot, — a major part of air pollution produced by gas and diesel engines. The concentration of ultrafine particles, which are smaller and penetrate deeper into the lungs, was likewise 1.7 times greater underground than at street level, researchers found.
Sources of Subway Air Pollution
The researchers argue that the subway mostly piles up all its particulate matter on itself. Graphite from brake pads is one of them and the wheels and rails wearing away are another. The problem is also attributed to the frequency of train operations, with the few minutes between trains not allowing outside air into the tunnels where oxygen levels are falling due to rising carbon dioxide and a small number of passengers relative to the confined underground spaces.
It is not the first time that air quality on subways in major U.S. cities has been scrutinized. A study of 71 public subway stations in cities such as Boston, New York and Washington, D.C., found the PATH stations in New Jersey and New York had the highest concentrations of fine particles. Yet the Philadelphia study was conducted across an ‘extended spectrum’ of particle sizes and types, revealing a more complete picture of air pollution.
Republication: Minding the Subway Grime, Solving for Air
The researchers identify several strategies that could help the City of Brotherly Love clean up its subway system — such as improved ventilation, platform screen doors and regular cleaning to cut down on dust buildup. They can also carry air purifiers to protect themselves from inhaling the dangerous particles.
The researchers do not recommend that commuters avoid the subway, however. The team reports that air pollution exposure levels can change dramatically between stations and day-to-day; moreover, the researchers observe that most people spend only short periods of time underground as part of their daily commutes. They suggest, though, that people with lung problems or other risk-factor health issues may want to wear N95 or surgical masks for protection.
The next phase of this research project will expose lung cells to the urban air pollution particles collected from the 15th Street Station and examine the oxidative stress produced by them. We can start to discern which, if any, properties of the particles are driving toxicity. The more researchers understand about the components to subway air pollution and what potential implications they have, the better informed scientists can be when strategies are formulated to improve the quality of subway air and protect train system users.
