Feb. 10 (UPI) -- All of the major subway systems on the East Coast trap polluted air in their stations, according to a new study.
But the air inside New York City's transit system, the world's most famous subway, is the most heavily polluted.
For the study, published Wednesday in the journal Environmental Heath Perspectives, researchers collected air quality data during morning and evening rush hours in 71 stations in Boston, New York City, Philadelphia and Washington, D.C.
Inside the 13 New York City Subway stations, levels of hazardous metals and organic particles in the air ranged from two to seven times the concentrations measured outside.
"Our findings add to evidence that subways expose millions of commuters and transit employees to air pollutants at levels known to pose serious health risks over time," lead study author David Luglio, a doctoral student at the NYU Grossman School of Medicine, said in a news release.
Inside the Christopher Street Station, a station on the PATH line connecting New Jersey and Manhattan, researchers measured concentrations of potentially dangerous particles 77 times greater than levels measured in the city air above ground.
The survey, which was conducted prior to the beginning of COVID-19 pandemic, found dirty air in all of the East Coast's transit systems, but none of the transit stations in Boston, Philadelphia or Washington, D.C., hosted air as heavily polluted as New York's worst subway stations.
"As riders of one of the busiest, and apparently dirtiest, metro systems in the country, New Yorkers in particular should be concerned about the toxins they are inhaling as they wait for trains to arrive," said co-senior study author Terry Gordon, a professor of environmental medicine at NYU Grossman.
The most polluted stations outside New York included: Capitol South in Washington, Broadway in Boston and 30th Street in Philadelphia
In addition to collecting more than 50 hours of real-time air quality data, scientists collected particles in air filters for analysis in the lab.
Roughly three-quarters of the particles found polluting the air in regional transit stations were iron and organic carbon.
Iron is mostly nontoxic, but organic carbon, which is released by decaying plants and animals or the incomplete breakdown of fossil fuels, has been linked with an increased risk of asthma, lung cancer and heart disease.
In followup studies, researchers plan to pinpoint the sources of dirty subway air. Scientists suspect fumes from diesel engines, decaying rodents and poor ventilation all play a role.