Photo: Julio Cortez / AP / Shutterstock
Particle pollution from vehicles and chimneys is a familiar sight for city dwellers, in the form of that black soot-laced film that settles on urban snow banks after a snowfall. But a new study found worryingly high levels of very fine particle pollution known as PM2.5 – named for the size of its particles, which penetrate deep into the lungs – in an unexpected place: within dozens of subway stations across the Northeast. And a stop in New York City, the Christopher Street PATH station, ended up having the worst air by far, with particulate pollution on the platform registering 77 times the concentration found in the air above the ground – a public health experience that is less how to breathe the normal dirt of the city and more how to inhale smoke from a fire on your daily commute.
Researchers at the NYU Grossman School of Medicine measured PM2.5 levels on 70-station underground platforms in New York City, Boston, Philadelphia and Washington, DC systems, as well as Long Island Rail Road and PATH train stations . Only 13 stations in New York City were analyzed as part of this study, but the department had already conducted a much larger survey of MTA stations in 2014 with similar results. This new body of research focused on re-evaluating MTA metro stations with the worst readings in the 2014 study, while trying to obtain comparable data on other systems. Two systems in the New York area recorded the highest number of PM2.5, with PATH stations averaging 392 micrograms per cubic meter and MTA metro stations coming in second, with 251 micrograms per cubic meter. Only Philadelphia’s was relatively low, at just 39 micrograms per cubic meter – which still exceeds EPA’s clean air levels. The data was collected before the coronavirus pandemic, and the researchers say they are not sure how nearly a year of reduced service may have changed air quality.
This does not mean that people should avoid the subway, warns David Lugilo, a doctoral student at NYU Grossman School of Medicine who was the lead author of the study. “I take the subway every day. I think the subway is a very good thing for cities because it reduces traffic on the roads, which reduces greenhouse gases, ”he says. But it is important to know that there is a risk, especially for certain groups of subway users, he notes. “Air pollution at these subway stations is likely to pose a significant health risk to individuals with pre-existing breathing problems, such as asthma, for passengers and workers.” Although no one discusses the superior air quality inside the subway cars – it is updated 18 times an hour – the air on the platform has not been evaluated as carefully, says Lugilo, which is where MTA representatives say they will look more closely. “We conducted previous air quality tests on metro trains operating on our system and found no health risks. However, we will thoroughly review this study, as the safety of customers and employees is always our top priority, ”said MTA’s Tim Minton. He added that the system is testing additional filtering technology for subway cars, while the system is getting ready to work 24 hours a day with the reopening of the city. For those who don’t spend a lot of time on the platform in general, the news is less alarming; the study says that adverse health effects are not likely with 15 minutes or less of exposure, and the average waiting time for the MTA is much shorter than that of rush hour trains, when most passengers are in transit.
Pollution by fine particles in our subways is not the same thing that comes out of car exhaust. It is largely created by the friction of steel wheels against steel rails and a “black carbon” generated by the constant friction of the brakes. (Some subway systems have rubber wheels on concrete rails and reduce the problem, but do not completely eliminate it.) In London, an investigation spurred by Mayor Sadiq Khan’s air quality initiatives caused the Financial Times declare the metro the “dirtiest place in the city” in 2019. Many of the world’s busiest transit systems have made major changes to address the problem in the past decade: London undertook an aggressive cleaning regime, Barcelona is experimenting with new station designs, and Seoul installed more than 800 air quality monitors across its subway system to share data publicly with passengers. A 2019 study that looked at various mitigation efforts such as fans and filters found the platform’s screen doors to be the most effective solution. These doors, which completely close the platform and only open when the train is completely stopped at the station, protect passengers from air pollution and also prevent people from jumping or falling on the tracks. Installing them in a system the size of New York would be an overwhelming task, and they were considered and rejected as part of the modernization work on the L train. Although not common in the US, many cities, including Singapore, have them all over the world. the system.
But even the platform doors do not universally protect workers, who Lugilo says are most at risk from high levels of underground pollution. What is dangerous about pollution in New York City’s subways, in particular, is that it includes high levels of iron, manganese and chromium, heavy metals that are much more destructive than the usual fossil fuel emissions to the lungs and are more likely to cause heart attacks and strokes. Nearly 140 MTA workers died of COVID-19, a disease that several studies have confirmed to be more serious for people exposed to high levels of particles. “Metro workers have one of the highest mortality rates,” says Lugilo. “I wouldn’t be surprised if air pollution had anything to do with it.” Fortunately, high-quality masks, something we hear a lot today, can be extremely effective in keeping viruses and PM2.5 at bay. If you plan to spend a lot of time underground, Lugilo suggests using one – which is, for better or worse, what MTA workers and passengers will do for a long time.