Subway system 10 times more polluted than outside, study shows

Waiting a long time for a subway can be annoying but a new study suggests it could do more than test your patience — it might also expose you to potentially harmful pollution.

According to a study published Tuesday in the journal Environmental Science & TechnologyEnvironmental Science & Technology, concentrations of fine particulate matter on the Toronto subway system are roughly 10 times the level found outside TTC stations. At 95 micrograms per cubic metre, researchers say the levels are typical of an average day in pollution-choked Beijing.

The study also found that concentrations measured on the TTC subway system were almost three times greater than those discovered on Montreal’s Metro and five times higher than those on Vancouver’s SkyTrain.

The lead author of the study, Keith Van Ryswyk, said the research didn’t measure the health effects of the pollution and the findings shouldn’t deter anyone from taking public transit.

But under some conditions, the kind of particulate matter that was measured, known as PM2.5, has been associated with lung problems, and Health Canada guidelines advise that indoor concentrations “should be kept as low as possible.”

“That is to say, there isn’t a safe level of PM2.5, so reducing it in any environment where people spend their lives every day is a good idea,” said Van Ryswyk, a researcher at Health Canada’s air health science division.

In a written statement, TTC spokesperson Stuart Green said the subway “remains a safe system for our customers and employees” and said the transit agency has been working for years to improve air quality underground.

The study was a collaboration between Health Canada, McGill University, and the University of Toronto, and was part of ongoing work to measure air quality in commuter environments, which represent a significant daily source of pollution exposure for millions of Canadians.