For cities like Toronto that strive to reduce pollution and greenhouse gas emissions, being compared to Beijing regarding air pollution levels is not what one would consider a compliment. Somehow, that’s a statement from University of Toronto professor, Greg Evans, in his description of fine particulate matter, an inhalable pollutant substance present in smog.
In a 2017 study led by Health Canada comparing air pollution levels between the Montreal metro, Toronto subway and Vancouver SkyTrain, concentrations of fine particulate matter (PM2.5) were much higher in Toronto’s system than in the two others, forcing the Transit Commission to issue a notice reassuring the public of its commitment to their health and safety.
Opened in 1954, the Toronto subway system is 80% outdoors, and has four lines covering a total track length of 76.9 kilometres. With a daily ridership of roughly 1 million commuters, it’s Canada’s second-busiest (after Montreal) and second-longest (after Vancouver) subway system.
Despite its impressive size, however, it also represents an important source of air pollutants. Just how bad is it? Well, Toronto’s subway system contains the worst levels of fine particulate matter (up to 100 micrograms per cubic metre)—three times more than Montreal and five times more than Vancouver.
Because outdoor air pollution standards don’t apply to subways, it is difficult to determine whether Toronto’s subway PM2.5 concentration is safe for workers and commuters. But, for comparison’s sake, consider that on a poor air quality day, the city’s outdoor particulate matter levels might rise to a maximum average of 30 µg/m³, a little bit less than the limit concentration of 35 µg/m³set by the U.S. Environmental Protection Agency.
So, while the Toronto Transit Commission (TTC) assures that subway air quality is safe, the lack of recent studies on the subway’s overall air quality as well as the TTC’s recent efforts towards reducing PM2.5 concentrations and the well-known impacts of fine particulate matter on human health may nonetheless suggest the contrary. So the question remains: Is using Toronto’s subway system safe after all? The answer is…
Yes, but not for everyone.
A. Air pollution and human health
A.1 What is air pollution?
Let’s begin by clarifying exactly what air pollution is. Basically, air pollution refers to a combination of different substances like carbon monoxide, fine particulate matter, nitrogen dioxide, ozone and sulfur dioxide in the air. In our case study about the Toronto subway system, we are looking mainly at fine particulate matter, which was found to be problematic—reaching an average 100 µg/m³, higher than Montreal or Vancouver.
Given that air pollution is responsible for an estimated 14,400 premature deaths in Canada each year, it’s easy to see why it is an important matter of public health that should be addressed on the government level.
A.2 Fine particulate matter
Fine particulate matter (PM 2.5) refers to a range of particles that are less than 2.5 microns in diameter. They are part of a wider range of particles called particulate matter, which range from 0.0005 to 100 microns in diameter, in solid or liquid form…or both. Fine particulate matter contains various substances like pollen, fungal spores, endotoxins and iron. Because of the microscopic size of these different substances, they can travel deep into the lungs when inhaled and cause a variety of illnesses, particularly those involving the respiratory system.
A.3 Effects of fine particulate matter on health
Health Canada warns that air pollution can affect breathing and lung conditions and heart conditions as well as linking it with strokes, asbestosis and Legionnaires’ disease. Fine particulate matter is notably associated with an increased risk of heart and respiratory diseases, lung cancer and reduced lung functions. It is most dangerous for: (a) children with asthma, as it affects breathing functions, (b) older adults, as it affects breathing, heart and blood functions, and (c) people with an underlying condition, which may get aggravated by exposure to poor air quality.
Although subway systems do not have limits for air quality, Health Canada suggests that particulate matter concentrations “be kept as low as possible”. With fine particulate matter levels 10 times higher than in the outside air, Toronto’s subway pollution logically raises serious health concerns among scientists, subway workers, commuters, as well as federal and local authorities.
B. Toronto’s subway air pollution
B.1 A preventable source of concentration
The fine particulate matter found in Toronto’s subway system contains mainly iron and manganese; furthermore, it reaches higher levels on the tracks than in the subway cars themselves. In fact, it’s the friction between the steel wheels and the steel tracks that is the primary source of particulate matter. Montreal’s metro, in comparison, runs on rubber wheels, concrete rails and a wood-based braking system. Therefore there’s less abrasion than in Toronto’s iron steel-on-steel wheels and rails. This difference in technology is confirmed by the difference in PM2.5 concentrations.
B.2 Is the Toronto subway safe?
For TTC, the subway has “typical” dust levels, similar to those of New York, London and Seoul, which all share same characteristics (iron wheels on steel tracks). Also, there is no scientific evidence linking Toronto’s subway fine particulate matter concentration to health problems in either commuters or subway workers.
The same has been concluded in a 2010 study led by Columbia University researchers trying to determine whether New York’s subway particulate matter concentration exposed subway workers to health complications. Nevertheless, the authors also recommended further investigation for more at-risk groups like track-maintenance and track-construction workers, children, the elderly and people with pre-existing respiratory conditions, given the association between PM2.5 exposure and respiratory diseases like lung cancer.
Basically, it means that the lack of scientific evidence of the subway’s PM2.5 effects on certain groups doesn’t prove its absence of health implications. In addition, the type of iron-charged fine particulate matter found in Toronto’s metro has been proven to be different and more toxic than your typical outdoor PM2.5, making TTC claims questionable.
The possibility of health issues therefore depends on each person’s immune system, respiratory health, metabolism and the duration of exposure. Given that most commuters usually spend less than an hour on the subway transit system, it remains relatively safe for users without known conditions or regular, prolonged exposure. Furthermore, efforts to reduce fine particulate matter levels should be implemented and regularly monitored.
Unfortunately, the last air quality study measuring various pollutants in Toronto’s subway system dates back to 1995 and is, with the absence of occupational exposure limits, one of TTC’s main arguments to certify the safety of Toronto’s subway air quality.
B. 3 Solutions
You may be wondering why they don’t just replace the wheels and rails. Even though this question seems the most evident, it doesn’t take into account how costly and disruptive such an undertaking would be.
Instead, the TTC has since initiated a series of ventilation and air cleaning solutions in order to reduce the subway’s fine particulate matter levels, following the recommendations of Health Canada. Improvements include:
• Improved air filtration on subway cars;
• A new track vacuum workcar equipped with HEPA filtration;
• Corridor cleaning program;
• Station and tunnel washing;
• Track clean-up crews; and
• T1 air duct cleaning program.
For the moment, conclusions are limited by a lack of research regarding air pollution in Toronto’s subway system, especially when it comes to its impact on commuters and workers. It is obvious that the concentration of PM2.5 far exceeds the safety limits, causing a plausible threat to people with respiratory conditions among others. Moreover, we are hopeful that future air quality studies of Toronto’s subway will assess current pollution levels and possibly make the TTC officially change its optimistic position on the subway system.
If you are worried about air quality in your home or work space, do not hesitate to get in touch with our Toronto Mold Busters experts team.