Study: Torontonians Breathe Easier in the Subway

The Subway Air Quality Initiative was conducted between 2018 and 2020. It was prior to this time that TTC deployed its new Bombardier (now Alstom) “Toronto Rocket” rolling stock on Line 1 and Alstom’s Urbalis 400 CBTC system with Automatic Train Operation (ATO) to optimize acceleration, deceleration and braking. These cars are also equipped with regenerative braking, which reduces the level of friction braking required.

Toronto Rocket transit at TTC’s  at St. Clair station. Photo courtesy the Globe & Mail.

The team found reduced levels of fine particulate matter (PM)—the mass of airborne particles smaller than 2.5 micrometers (PM2.5) per cubic meter of air—on trains and platforms when compared with previous measurements taken between 2010 and 2011, when the previous series of cars were in service.

The research team included UofT Professor Greg Evans from the Department of Chemical Engineering & Applied Chemistry and Institute for Studies in Transdisciplinary Engineering Education & Practice (ISTEP), and Health Canada researcher Keith Van Ryswyk, who has been studying air quality in subway systems for more than 10 years and is now completing a Ph.D in the Department of Chemical Engineering & Applied Chemistry. National Research Council Canada provided support.

Evans and Dr. Cheol-Heon Jeong, both of whom serve at the university’s Southern Ontario Centre for Atmospheric Aerosol Research (SOCAAR), in 2017 conducted a study for Metrolinx on commuter train diesel exhaust and its potential effects on passengers.

“Observed levels [of PM2.5] fall well below the occupational exposure limits, and are now as much as 10,000 times lower than they were in the first such study, conducted in 1995,” TTC said.

The University of Toronto Engineering News provided the following details:

“The team found that PM2.5 levels on Toronto’s Line 1 platforms decreased by about 30%, and levels inside Line 1 trains dropped by about 50% compared to 2010-11 levels. This finding is likely due to a complete changeover to newer trains.

“On Toronto’s Line 2, where the new trains have not yet been rolled out, the results were more mixed. The researchers initially observed an increase in the levels of PM2.5 by almost 50% on the platform and 13% inside the Line 2 subway cars compared to 2010-11. The cause of the increase was identified as being related to brake dust—subsequent changes in braking patterns after 2018 corresponded to PM2.5 levels below those measured in 2010-11.

“The researchers compared PM2.5 in newly built subway stations against older stations to see whether dust built up over the decades was a factor. They observed that it didn’t take long for the air in new stations to become like the old ones—indicating that legacy dust was not the issue, and that new dust from braking materials and behavior were likely the two biggest contributors to air quality levels.

“The composition of the airborne particles inside TTC stations and trains also gave a clue as to their origins: They’re high in certain metals, such as barium and iron oxides, suggesting that they’re likely thrown off by the trains’ friction brakes, more so on the older model subway cars.”

According to TTC, the research also found that air quality in Toronto’s subway system is comparable to the quality found in other large underground rail systems, and in some cases is better than other major subway systems such as New York City and Boston.

TTC acting Chief Safety Officer Betty Hasserjian

“This is excellent news for our employees and customers, and it confirms that the steps we have taken to date are having a positive impact on air quality,” TTC’s acting Chief Safety Officer Betty Hasserjian said. “We will keep modernizing our infrastructure and our operating procedures to ensure we are continuing to make gains in this area.”

“I’m pleased to see the work the TTC is doing has resulted in a lowering of PM2.5 levels in the subway system,” Toronto’s Medical Officer of Health Dr. Eileen de Villa said. “There are numerous benefits that public transit offers with respect to the city’s overall air quality by reducing traffic congestion and associated air pollution.”

Railway Age Editor-in-Chief William C. Vantuono contributed to this story.

Toronto Rocket car interior. William C. Vantuono photo.

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