Despite several improvements, air quality in Toronto’s subway system still falls short of international standards, according to a study from a team of chemical engineering students at the University of Toronto.

“We’ve been interested in subway air quality for over a decade,” said Professor Greg Evans. “On Line 2, air quality has remained about the same, and it’s not great compared to many subway systems around the world,” he said.

As part of the study, six students rode the full length of Line 2, spending about two hours per trip collecting air samples.

They found a mix of particles in the air, including trace metals like copper, chromium, and zinc.

While there’s no official threshold for health impacts, Health Canada advises that levels of particulate matter be kept as low as possible

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