From tires to brakes, U of T researchers tackle 'non-tailpipe' air pollution from vehicles

With the increasing popularity of electric vehicles, car-related air pollution will be less of a concern, right? Think again, say a group of University of Toronto researchers who are studying the effects of air pollution from brakes and tires. 

While the push to mandate EV aims to reduce tailpipe emissions such as carbon dioxide – the federal government has set a target of complete EV adoption by 2035 – swapping every vehicle on the road still won’t eliminate all the sources of air pollution that can impact human health.

That’s because brake pads, rotors and tires grind down over time and erode. This results in tons of particulate matter like heavy metals and microplastics polluting the air. 

“Millions of tires being driven on the road breaking down –that’s a problem,” says Matt Adams, an assistant professor in U of T Mississauga’s department of geography, geomatics and environment.  “It’s an emerging question in the field – it’s hard to know where the particles end up.”  

Adams and Greg Evans, a professor of chemical engineering and applied chemistry in U of T’s Faculty of Applied Science & Engineering, belong to a team of U of T researchers who are conducting a three-year study to learn more about tailpipe vs. non-tailpipe emissions. The study is for a U.S.-based organization called the Health Effects Institute, which gathers research on the effects of air pollution. Other researchers include: Professor Marianne Hatzopoulou and Associate Professor Arthur Chan in the Faculty of Applied Science & Engineering; Associate Professor Meredith Franklin in the department of statistical sciences in the Faculty of Arts & Science; and McGill University’s Scott Weichenthal and University of Barcelona visiting professor Maria Pérez. 

Evans says the source of vehicle pollution has shifted in recent years.  

“Because of changes in vehicle technology, tailpipe emissions particularly from cars has dropped off a lot over the last two decades,” Evans says. “What we found with research we’ve done in Toronto is that, since 2013, non-tailpipe emissions have exceeded tailpipe emissions.” 

While tires are made from a combination of plastics and rubber, brakes are made of heavy metals, including iron, barium and copper. 

Particles of heavy metals, microplastics and micro rubber from tires and brakes pollute the air and can contribute to a range of negative health outcomes. Some heavy metals like copper can cause oxidative stress when inhaled. Lungs suffer from inflammation and an immune response is triggered. 

“There is not an organ in your body that’s not impacted by air pollution,” Adams says. “We know your health risk is increased. We know a lot of these pollutants are carcinogens. [It] can contribute to cardiorespiratory issues.” 

Evans says the researchers hope the study will improve methods of gathering vehicle pollution data.

“At the end of it, we’re hoping to have better methods to able say how much is coming from tailpipe and how much is non-tailpipe, and how do we identify hot spots,” he says. 

The findings could potentially result in regulations for tire and brake emissions. In late 2022, the EU proposed new Euro 7 standards to reduce vehicle emissions and improve air quality. The new proposals were the first worldwide emissions standards to set additional limits for emissions from tires and brakes. 

Greg Evans, a professor of chemical engineering and applied chemistry, says his research shows that non-tailpipe emissions have exceeded tailpipe emissions in Toronto since 2013 (supplied photo)

Adams says there are additional considerations when switching over to EVs, including the source of electric power, lithium sourcing and related infrastructure. 

“We’re trying to translate the links of how and where you are in the urban environment to your exposure [to air pollution], and then using that to plan cities better for our health,” Adams says. 

Planning more healthy cities means building urban areas where people can walk, cycle and take public transit in addition to adopting EVs. 

“Air pollution is tricky,” Adams says. “It’s invisible for the most part –we don’t smell it. We’re trying to quantify the intangible for the average person.”