Photo: Julio Cortez / AP / Shutterstock
Private pollution by vehicles and smoke piles is a familiar sight to urbanites, in the form of the black black soot film that settles on urban snow banks after a snowstorm. But a new study has found alarmingly high levels of the very fine contamination of particles known as PM2.5 – named after the size of the particles that penetrate deep into the lungs – in an unexpected place: within dozens of subway stations throughout the Northeast. And one stop in New York City, the Christopher Street PATH station, has by far the worst air, with particulate matter pollution on the platform registering 77 times the concentration in above-ground air – a public health experience that is less than being in normal slowness and more like inhaling wildfire smoke on your daily commute.
Researchers from NYU’s Grossman School of Medicine measured PM2.5 levels on the platforms of 70 subway stations in New York City, Boston, Philadelphia and Washington, DC, as well as stations for the Long Island Rail Road and the PATH train. Only 13 stations in New York City were analyzed as part of this study, but the department conducted a much larger survey of MTA stations earlier in 2014 with similar findings. This new investigation focused on re-evaluating the MTA metro stations with the worst measurements from the 2014 study, while attempting to obtain comparable data on other systems. Two New York regional systems recorded the highest for PM2.5, with PATH stations averaging 392 micrograms per cubic meter, and MTA subway stations ranked second at 251 micrograms per cubic meter. Only Philadelphia’s was relatively low, at only 39 micrograms per cubic meter – which still exceeds the EPA’s cleaning levels. The data was collected before the coronavirus pandemic, and researchers say they are not sure how the air quality could change for almost a year of reduced service.
That does not mean people should avoid the subway, warns David Lugilo, a doctoral student at the NYU Grossman School of Medicine, who served as lead author of the study. “I ride the subway every day. I think metros are a very good thing for cities, because they reduce road traffic, which reduces greenhouse gases, ”he says. But it is important to know that there is a risk, especially for certain groups of metro riders, he notes. “The air pollution in these metro stations is likely to pose a significant health risk to individuals with pre-existing respiratory health conditions such as asthma, to commuters as well as workers.” While no one is debating the superior air quality in subway vehicles – it is being refreshed 18 times an hour – the air on the platform has not been so carefully evaluated, says Lugilo, this is where MTA representatives say they will take a closer look. ‘We have done previous air quality tests on metro trains operating in 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 Tim Minton, MTA. He added that the system is launching additional filtration technology for metro cars as the system is ready to move back to 24-hour service as the city reopens. For those who do not spend much time on the platform, the news is less disturbing; the study says adverse health consequences are unlikely to be with exposure to less than 15 minutes, and the average waiting times for MTA are much lower than the peak times, when most passengers drive through.
The pollution of fine particles in our metros is not the same thing that comes from the exhaust pipes of cars. It is largely created by the friction of steel wheels against steel rails, and a ‘black carbon’ produced by the constant grinding of brakes. (Some metro systems have rubber wheels on concrete tracks, and this reduces the problem but does not eliminate it completely.) In London, an investigation spurred by Mayor Sadiq Khan’s air quality initiatives Financial Times to declare the Tube the “dirtiest place in town” in 2019. Many of the world’s busiest transit systems have undergone major changes over the past decade to address the problem: London has embarked on an aggressive clean-up regime, Barcelona is experimenting with new station designs, and Seoul has installed more than 800 air quality monitors throughout its metro system to share data publicly with passengers. A study from 2019 in which various mitigation efforts, such as fans and filters, were interviewed, considers platform screen doors to be the most effective solution. These doors, which completely enclose the platform and only open when the train has stopped completely at the station, would protect passengers from air pollution and also prevent people from jumping or falling on the tracks. Installing them in a New York-sized system would be a big task, and they were considered and then rejected as part of the modernization of the L-train. Although not common in the US, these are systems across the country, including Singapore.
But even platform doors will not protect workers, which, according to Lugilo, posed the greatest danger due to high levels of underground pollution. What is particularly dangerous about the pollution in the New York subways is that it contains elevated levels of iron, manganese and chromium, heavy metals that are far more destructive than ordinary fossil fuel emissions to the lungs, and which are more likely to to cause heart. seizures and strokes. Nearly 140 employees of MTA have died from COVID-19, a disease that has been confirmed to be more serious for people exposed to high levels of particles. “Metro workers had some of the highest death rates,” says Lugilo. “I would not be surprised if the air pollution had something to do with it.” Fortunately, high-quality masks, something we hear a lot about these days, can be extremely effective in keeping out both viruses and PM2.5. If you plan to spend a lot of time underground, Lugilo suggests wearing one – which is good or bad that MTA workers and commuters will do for a long time.