Air pollution in Philadelphia metro far worse than on streets, study finds

The air quality in the City Hall subway station in downtown Philadelphia is much worse than on the sidewalks directly above the station. This is a key finding of our new study published in the Journal of Exposure Science and Environmental Epidemiology.

We are an environmental scientist and biochemist who assessed air quality at 15th Street-City Hall Station in Philadelphia. We focused on this station because our previous study found it had the highest particle levels among the 12 Philadelphia subway stations we measured on the busy Market-Frankford or Broad Street lines.

Most worryingly, we found that there was about 10 times more black carbon inside the station than at street level. Black carbon, commonly known as soot, is a major component of fine particle air pollution. It is emitted during incomplete combustion of fossil fuels and biomass burning, and its inhalation is associated with adverse health effects such as asthma, heart attacks and lung cancer.

Our results suggest that black carbon is generated by the subway system itself. Graphite used on brake pads is a potential source.

We also found that levels of ultrafine particles, or UFPs, were about 1.7 times higher underground than on the surface. While fine particles measure up to 2.5 microns in diameter, or about 35 times smaller than a grain of fine beach sand, ultrafine particles measure 0.1 microns or less. These particles are a concern because they penetrate deep into people’s lungs.

Limited access to outside air, frequency of trains, large number of passengers and its location in the heart of downtown may be some of the reasons for high particle concentrations at the 15th Street station.

Subway air quality has previously been studied in Philadelphia and several other U.S. cities, including Boston, New York and Washington, DC. A study of 71 subway stations in these metropolitan areas found that PATH stations in New York and New Jersey had the highest concentration of fine particles. This study also found a similar concentration of fine particles, mainly iron and carbon, in Philadelphia as we found.

Our study, however, measured more particle types and sizes.

Our study highlights the need for Philadelphia to monitor air quality in its subways and reduce air pollution exposure for commuters and subway workers.

Several major factors contribute to metro air pollution. These include subway age, wheel and rail wear, train frequency, use of graphite lubricant on brake pads, poor ventilation, station depth and limitations access to outside air and outside circulation.

Having better ventilation, using screen doors, and cleaning more often to minimize dust are some ways to improve air quality.

Although we believe that subway air quality needs to be improved, our results do not suggest that commuters should avoid taking the subway. Air pollution levels vary greatly between stations and over time, and commuters spend relatively short periods of time inside metro stations.

People with health conditions, including lung disease, can get excellent protection by wearing an N95 mask or even a surgical mask. Subway workers can use air purifiers to reduce their exposure to particle pollution.

We simultaneously measured particle pollution in the underground subway platform and in the surface pedestrian route using three types of monitors. We took measurements six hours a day, from approximately 9 a.m. to 3 p.m., five weekdays during the summer of 2022.

The next step in this project involves exposing lung cells in the laboratory to air pollution particles from the 15th Street station and measuring the oxidative stress caused by these particles. This stress contributes to chronic diseases, including asthma, chronic obstructive pulmonary disease and lung cancer.

We will also look at the types of air particles and the levels of various metals they contain, to determine whether these particles from the subway are causing stress on lung cells.

This article is republished from The Conversation under a Creative Commons license. Read the original article.