Does particulate matter matter?

Story by Tammy Thorne and Cayley James

The benefits of cycling far outweigh the risks.

That's the introductory slide for the summary presentation for new research regarding particulate matter in the bike lane.

Last month, U of T professor Marianne Hatzopoulou presented her team’s research with the clear and concise introductory disclaimer in all caps:


It is followed by further enforcement: "If you are a healthy individual, the physical activity benefits largely offset air pollution exposure. If you have asthma, diabetes, a cardiovascular condition, you may not want to ride on poor air quality days."

The reason the Transportation and Air Quality Research Group conducted this research are simple. Air pollution remains a problem and cyclists are breathing deeply as they pedal in bike lanes that are often adjacent to major roads.

Hatzopoulou, Canada Research Chair in Transportation and Air Quality at U of T, began research on this topic while she was working at McGill University. And while you won't see many people riding their bikes wearing medical masks or air purification breathing devices over their mouths and noses here in a city sometimes called "The Big Smoke" by out of towners, pollution - particularly, particulate matter - is something that those of us who pedal about town do feel in our lungs and throats some days. It helps that the province finally shut down coal plants in 2014, but traffic-related air pollution is still a big problem for Ontarians. Rapid changes in vehicle technology have led to gains in fuel efficiency but not necessarily in the emissions of air pollutants.

To conduct the research, cyclists (and pedestrians) were fitted with air quality monitors. There were 10 chosen cycling routes. (You can find more details on the methodology here.) The chart below shows the block-by-block measurements.

Ultrafine particles refer to particles of diameter 100nm or less, mostly produced from combustion reactions. In urban areas, they are primarily generated by traffic exhaust. Due to their small size, they are able to penetrate deep into the lungs and have been associated with a range of health effects. And, generally speaking, cyclists have the highest exposure among other road users.

A quick glance at the colour-coded average UFP map shows that busy roads are where they found higher particulate matter.

We asked Hatzopoulou, who is a professor in civil engineering, to explain why this research is important, most especially for us every day city cyclists.

“Downtown streets with their dense buildings on both sides have extremely high levels of ultrafine particles (UFP)  — this can help us identify roads that are best candidates for traffic reduction measures. Coincidentally bicycle facilities that attract the most cyclists also have the highest levels of UFP,” she says.

Air pollution is associated with more deaths in Canada annually than traffic accidents or breast cancer or prostate cancer. Exposure to pollution during busy commute times is also higher than the average throughout the day. There is a large spatial variability in UFP levels which means that two adjacent roads can exhibit very different levels - and this is good news. It means that vulnerable individuals can change routes.

Hatzopoulou says the project is “about how we can design streets and urban microenvironments that promote healthy lifestyles and do not penalize cyclists for giving up their cars.”

Once they tallied the data they compared it to the Montreal study. Toronto, embarrassingly, has both a mode and median that trumps the Montreal’s UFP levels by a couple of thousand.  

As for whether the installation of the much debated Bloor bike lane pilot project has changed air pollution level, the group is yet to see the before and after results. But she says, “traffic reductions on Bloor will certainly be associated with reductions in near-road air pollution and reduced exposures to pedestrians and cyclists.” (There has been a 22 per cent reduction in motor vehicle traffic on Bloor recorded, thus far.)

Hatzopoulou doesn't currently bike on Bloor because the bike lane doesn't go far enough west to serve her commute in from Islington. But what if the bike lane were extended?

"Of course I would bike on Bloor if there was a protected bike lane that went all the way! The bike network in Toronto in very fragmented and there is so much more that needs to be done. This being said, I am a researcher not an advocate. I am always very concerned about the media portraying academics as advocates for one thing vs another. I refuse to play that role," she says. "I simply do good research that is based on science and can be published in reputable scientific journals."

Hatzopoulou and her team are now planning the next steps of applying the data. First they will generate a map of UFP across the city in order to estimate levels along roads that were not sampled. Then they’re planning on intersecting these with GPS data for a large number of bike trips to look at the average exposure of a typical cyclist in Toronto. Hatzopoulou will also be updating the CleanRideMapper web application.

You can see the entire presentation here.

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Bring on the data!


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