Language selection


The air around us: Evidence from the Subway Air Quality Study

Have you ever wondered about the quality of the air that you breathe while you are stuck in traffic? Keith Van Ryswyk, a researcher on air pollution exposure at Health Canada, has been looking into it and the results are interesting.

Airborne fine particulate matter, known as PM2.5, are a mixture of liquid and solid particles smaller than 2.5 micrometers. Their chemical make-up varies and they can get deep into your lungs and cause health issues in the long and short term. Canada has made significant contributions to understanding the health effects of PM2.5 and this evidence has informed air quality policy around the world. Keith is specifically examining the particles we find in commuting environments to inform actions to reduce Canadians’ exposures.

It all started with backpacks. In 2005, as a research assistant, Keith was involved in air pollution research studying the personal PM2.5 exposures of asthmatic children. One of his objectives was to better understand how children’s exposure to PM2.5 can vary depending on their daily activities. Each child carried a diary and a backpack. The backpacks contained a PM2.5 monitor taking measurements every second and the children recorded their activities in the diary. Turns out, these studies and others like it seem to suggest something interesting about getting to school or work; while commuting can represent a small portion of your day, it can make a big contribution to your daily PM2.5 exposure. That got Keith thinking about commuting, and the air we breathe on buses, cars and subways and how this information could be used to inform policies to reduce Canadian exposure to air pollutants.

Keith soon found out that there was very little data available about air pollution levels in Canadian commuting environments. So in 2010, he designed a study to measure air pollution levels in the commuting environments of Toronto, Montreal, Vancouver, and Ottawa, which has led to some interesting findings. The mixture of air pollutants in each commuting method are very different. In private vehicles and buses, people are exposed to pollutants related to gas and diesel exhaust. Subways, on the other hand, have electrical propulsion and are generally removed from street and highway vehicle exhaust. The major particulate matter sources in subways are rail, wheel, and brake components from train activity. The constant wear of these materials can result in high levels of PM2.5, which can become concentrated in confined underground spaces.

The subway systems of Montreal, Toronto, and Vancouver are among the largest in North America. Combined, they normally carry 2.5 million Canadians to work every day. These three systems are very different in their design. The Vancouver SkyTrain system is largely outdoors and elevated, while most of the Toronto subway and all of the Montreal metro are below ground. As well, the trains of Toronto and Vancouver have steel wheels and metallic brake shoes while the wheels of the Montreal system are rubber and its brake shoes are made of peanut-oil treated wood – which they make themselves. These differences in design have led to significant differences in PM2.5 levels and composition.

PM2.5 has been linked to a range of health outcomes including respiratory and cardiac disease and reduced lifespan. However, almost all of this research has been done in outdoor environments. Subway PM2.5 is very different from that of outdoors. The particulate matter that Keith’s team and other groups have found in the subway systems are highly enriched in steel-based and brake-related elements. “We need to better understand the components of particulate matter that drive its toxicity. Answering this research question would be very valuable towards better management of airborne particulate matter,” says Keith.

Another objective of Keith’s work will be to test ways in which subway PM2.5 can be reduced. The initial study estimated that the more than half a million Canadians who spend 5% of their day in the Toronto subway get 21% of their daily PM2.5 exposure during their commute. If a small reduction in the PM2.5 levels in this system could be made, it could make a big difference for the daily PM2.5 exposures for a large group of Canadians.

Each commuting method is essential to our economy, especially public transit, and it is essential to ensure the health and safety of its users. Clean air is an important part of that. In order to address this issue, Keith has been investigating ways in which air quality in public transit can be sustainably improved.

Since the beginning of this study, Keith has been working closely with the Toronto Transit Commission (TTC) to develop ways of testing what changes might influence the levels of PM2.5 in the subway. New tests have been carried out on platforms in coordination with measures already being adopted by the TTC to improve the subway. Data is being analysed to determine what makes a difference. For decades, the TTC has ensured that the occupational air standards, set by the Ontario Ministry of Labour, are met. In fact, the TTC just completed an air quality study, and none of the levels exceeded the regulations set forth for the workers who spend their days in the subway system.

The subway air quality research is an example of what Health Canada is doing to contribute to a foundation of evidence and to establish guidance on air quality management, including recommendations on mitigation measures for commuting environments upon which policy can be designed to improve the lives of Canadians, now and for years to come.

Date modified: