Results from a new study has revealed that Toronto Transit’s air pollution is ten times worse that the air outside. Heath Canada who carried out the research recommends that these levels should be kept as low as possible and that subways increase our personal exposure to certain toxic pollutants. The findings highlight that Toronto's Transit Commission (TTC) has the poorest air quality in Canada. Its pollution levels are three times worse than Montreal’s metro but Vancouver’s SkyTrain is rated as the cleanest.
"On a poor air quality day in Toronto, it is possible for this value to rise as high as 30 micrograms per cubic metre meaning the particles would be visible in the air as haze."
The investigation was carried out by using an air quality metric called PM2.5 in 2010-11 which measures the amount of airborne particles which are smaller than 2.5 micrometres per cubic metre of air. "While larger particles get caught in your nose or throat, these ones can make the twists and turns to be able to get deep down into the lungs," says University of Toronto Engineering professor Greg Evans. Whereas, a human hair is 50 to 100 micrometres wide. According to Evans, a typical outdoor PM2.5 value for Toronto would be on the order of ten micrograms of particles per cubic metre of air. On a poor air quality day in Toronto, it is possible for this value to rise as high as 30 micrograms per cubic metre, meaning the particles would be visible in the air as haze.
It was even claimed that Toronto’s subway platforms and trains were comparable with a normal day in Beijing. What is surprising is that whilst the streets have more combustion sources from cars and trucks, subways are electric. The research suggests that the particles must be coming from elsewhere. "We know from analysing the composition of the particles that it's not just everyday grime," says Evans.
"The metal concentrations are very high, and the ratios of manganese to iron are similar to what you see in steel." This composition suggests that abrasion between the wheels and track of the train is grinding off tiny steel particles. As each train comes into the station, it pushes a column of air in front of it, which stirs up these particles along with any other dust settled at track level.
Health Canada’s report states that exposure to these levels of pollution could be reduced by upgrading ventilation systems and cleaning up the dust that may be the source of the particles. However, they do acknowledge that since the study was carried out, Toronto’s Line 1 has introduced new cars which could already be reducing better braking systems and improved air filters, although these studies have not yet been done.
In the meantime, Evans says he will continue using subways for his daily commute, at least when biking is not an option. "Public transit offers the advantage of better air quality overall across the city," he says. "This isn't enough for me to stop taking the subway, but at the same time, we should try to reduce our exposure."
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