Black carbon fouls New York subway stations

Among the grit and grime cloaking New York City’s subway stations, one type of tiny, sooty particle looms large. Black carbon, an easily inhaled byproduct of burning diesel fuel, clogs the air of underground stations along several subway lines; particle levels can reach an average of seven times as high as those at the roadside, a new analysis suggests.

Researchers knew that subway air was dirty — wheels grinding along metal rails fill tunnels with steel dust, for example­ — but until now, no one had measured NYC stations’ black carbon. High levels of the fine airborne particles also have been found at subway stations in Amsterdam and Helsinki, though New York City’s stations may claim the title for most polluted, researchers report November 19 in Environmental Science & Technology.

Passenger trains in New York City use electricity, but maintenance trains still run on diesel and trigger spikes in underground black carbon levels. Breathing in too much black carbon could spark respiratory problems such as asthma.

Editor’s Note: This story was updated December 8, 2014, to correct the name of one of the subway stations in the graph.