New York City subway riders are breathing in hazardous air, study finds

New York City subway riders are breathing in hazardous air, with Black and Hispanic commuters exposed to higher levels of pollution, a new study shows.

New York University researchers found that the average subway platform had four times the particulate pollution (PM2.5) exposure standard deemed safe over a 24-hour period by the Environmental Protection Agency, and nine times the exposure guideline set by the World Health Organization.

The researchers note that although commuting time is only a portion of the entire day, riding the subway accounts for a significant portion of a person’s daily exposure to PM2.5.

“At that size, these particles penetrate the lung, and it’s been shown that small particles cause issues with cardiovascular, respiratory and neurological diseases,” said Masoud Ghandehari, the lead researcher and a professor of urban systems engineering at New York University. “We have 5 million riders per day. Imagine the human impact one may be having in a single day in the New York City subway system.”

The burden of air pollution disproportionately falls on low-income people and communities of color, both above ground and below. By looking at census block data for ethnicity and income, researchers found that low-income New Yorkers and people living in majority Black and Hispanic communities have longer, more frequent commutes. That, in turn, leads to higher exposure to dangerous air pollutants. The study found that Black and Hispanic workers endure PM2.5 levels that are 35% and 23% higher, respectively, than Asian and white commuters.

“Most jobs are in financial districts in New York City, [such as] midtown and downtown Manhattan,” Ghandehari said. “Those with lower income oftentimes live further away from these job centers. So their commute time ends up being longer, which means their exposure is going to be higher.”

The researchers found a staggering concentration of iron within the fine particles they analyzed. That is largely due to wear and friction of trains’ metal wheels, brakes and rails, they said. Older, deeper, busier stations with poor ventilation had higher concentrations of PM2.5.

“Whatever pollutants that are brought from the outdoor air get trapped and recirculated,” said Kabindra Shakya, an assistant professor of geography and the environment at Villanova University who was not involved in the study. “Above ground, there is more chance for dispersion, wind speed carrying away and cleaning it, whereas it’s being accumulated [underground] with less ventilation.”

In 2020, Shakya and his team found that the level of air pollution in Philadelphia’s subway systems was roughly four times that of aboveground. They also found that stations with less direct outdoor access had higher concentrations of particulate matter.

He described the risk to people with short commutes as “minimal”, but added: “I want to emphasize that occupational workers, like subway workers or the vendors who work [there], are at the most risk.”