People traveling on subway systems in major US cities are being exposed to unsafe amounts of air pollution, with passengers in New York and New Jersey subject to the highest levels of pollution, the research found.
Tiny particles suspended in the air, probably released by train brakes or friction between train wheels and tracks, are abundant in the 71 underground stations sampled by researchers during morning and evening peak hours in Boston, New York, Philadelphia and Washington DC, the cities that contain most subway systems in the USA.
The levels of these tiny pollution particles, called PM2.5, were well above the nationally determined daily safe levels of 35 micrograms per cubic meter in each city. New York’s Metropolitan Transit Authority (MTA) system was 251 micrograms per cubic meter, followed by Washington DC with 145 micrograms per cubic meter. Philadelphia was, by comparison, the cleanest system, but it still crossed the threshold beyond which serious health risks are subject.
“New Yorkers in particular should be concerned about the toxins they are inhaling,” said study co-author Terry Gordon, professor at the Grossman School of Medicine at New York University, with the research finding that concentrations of dangerous metals and particles organic matter was anywhere from two to seven times that of the city’s outdoor air samples.
Christopher Street, a Manhattan station that helps connect New York and New Jersey, had an incredible level of particle pollution of 1,499 micrograms per cubic meter, about 77 times greater than above-ground pollution. This is a level of pollution most commonly encountered near a major fire or during the demolition of a building, the researchers said.
“It was the worst pollution ever measured at a subway station, higher than some of the worst days in Beijing or Delhi,” said Gordon, who said he was so surprised by the readings on his instruments that he had to ask colleagues to perform repeated tests to make sure the numbers were correct. “It just wasn’t credible. My colleague went down there and his airways were tight after an hour or more. “
The researchers calculated that someone who takes a typical round trip to Christopher Street increases the risk of an adverse cardiovascular event by 10%. But the station was not the only one with high airborne toxins, with Broadway in Boston, Second Avenue in New York and 30th Street in Philadelphia among the most polluted stops in the northeastern United States. “People should be very alarmed by these high levels,” said Gordon.
Subway systems typically transport millions of people across US cities, with the New York City MTA, the largest in the country, transporting 5.5 million people around New York every day in 2019. Metro use has plummeted during the coronavirus pandemic, however, with many of the remaining passengers are those working in essential frontline jobs.
The analysis of the air samples shows that the pollutants were composed mainly of iron and organic carbon, a chemical produced from the degradation of fossil fuels or of decomposing plants and animals. The latter, when inhaled, was associated with an increased risk of respiratory problems, lung cancer and heart disease. It is not entirely clear why pollution in the subways is worse than on the surface, although the open air is able to dilute and remove some of the smoke from cars and trucks, while underground stations are often poorly ventilated.
Gordon emphasized that more research is needed to determine the exact impact on the health of passengers and public transport workers, who spend a lot of time at polluted stations. The researchers also plan to further explore the exact sources of the pollutants, which can range from the exhaust provided by diesel locomotives to the dust raised from the remains of dead rodents.
“This is an important contribution, especially to our understanding of the disproportionate burden of air pollution faced by low-income communities and communities of color,” said Gretchen Goldman, research director at Union of Concerned Scientists, who was not involved in the study. , which was published in Environmental Health Perspectives.
“As the scientific community works to better understand the exposure and potential effects of air pollution on the urban environment for health, I hope that local decision makers will use this valuable work to inform the best ways to address the known racial and socioeconomic inequalities in exposure to air pollution in US cities. “