Most Canadians breathe these particles every day without knowing it.
In the slow accumulation of daily breath, cities shape the health of their people—and their inequities. A McGill University study now quantifies what cleaner transportation could mean for Montreal and Toronto: more than 3,600 premature deaths prevented by 2040, simply by reducing the ultrafine particles that pour invisibly from vehicle exhaust into lungs and bloodstreams each day. The particles remain unregulated despite decades of mounting evidence, and the communities breathing the most of them are rarely the ones with the most power to change that. This research places a number on a moral question that has long resisted easy accounting.
- Ultrafine particles from vehicle exhaust penetrate deep into the body, triggering heart and lung disease, yet no Canadian regulation currently limits them—leaving millions exposed without recourse.
- The gap between what science knows and what policy has acted on is widening, and the McGill team's findings add urgent pressure to close it before another decade of preventable deaths passes.
- The most ambitious modeled scenario—rapid EV adoption, accelerated retirement of pre-2007 diesel trucks, and reduced traffic—would prevent over 3,600 deaths across both cities by 2040.
- Even a modest path, holding traffic steady and retiring only the dirtiest trucks, could still prevent more than 3,300 deaths, suggesting the floor of benefit is already high.
- The gains would fall most heavily where the burden has always been greatest: low-income neighborhoods and communities of color clustered near major roads, where the air is worst and the political voice has been quietest.
Researchers at McGill University have modeled what two of Canada's largest cities could gain by following through on their own climate commitments. The answer, rendered in human lives, is striking: more than 3,600 premature deaths prevented in Montreal and Toronto by 2040, if both cities move decisively toward cleaner transportation.
The threat being addressed is ultrafine particles—microscopic pollutants released in vast quantities by vehicle exhaust. Because of their size, they bypass the body's defenses and settle deep in the lungs and bloodstream, where they contribute to heart disease, lung disease, and early death. Most urban Canadians breathe them daily without knowing it, and despite growing scientific certainty about their harm, they remain entirely unregulated. Lead author Marshall Lloyd called that gap troubling, noting that policy has simply not kept pace with the evidence.
The McGill team grounded their projections in real targets already adopted by Toronto and Montreal, then modeled what would happen if those plans were actually carried out. Their most ambitious scenario combined rapid electric vehicle adoption—reaching roughly half the fleet by 2030 and nearly all vehicles by 2040—with accelerated retirement of older heavy-duty diesel trucks and a reduction in overall traffic. That path would prevent approximately 1,100 deaths in Montreal and more than 2,500 in Toronto.
A more modest scenario proved nearly as compelling. Even without a surge in EVs, phasing out the oldest and dirtiest diesel trucks while keeping traffic stable could still prevent over 3,300 deaths across both cities—suggesting that meaningful progress does not require a complete transformation of how people move.
Senior author Scott Weichenthal underscored where the benefits would be felt most acutely: in neighborhoods near major roads, where low-income households, immigrant communities, and visible minorities are disproportionately concentrated and already breathing the worst air. Cleaner transportation, the study implies, is not only an environmental policy—it is a decision about which communities are protected and which continue to bear costs they did not choose.
Researchers at McGill University have modeled a future where two of Canada's largest cities dramatically reduce vehicle emissions—and the numbers are stark. If Montreal and Toronto shift decisively toward cleaner transportation over the next fifteen years, more than 3,600 premature deaths could be prevented by 2040. The culprit being addressed is ultrafine particles, microscopic pollutants that pour from vehicle exhaust in enormous quantities and, because of their size, slip deep into the lungs and bloodstream where they trigger heart disease, lung disease, and early death.
Most Canadians breathe these particles every day without knowing it. They are everywhere in urban air, yet they remain unregulated—a gap that Marshall Lloyd, the study's lead author and a research associate in McGill's Department of Epidemiology and Biostatistics, finds troubling. "Most Canadians are exposed to UFPs on a daily basis and these pollutants are not currently regulated, despite growing evidence linking them to increased mortality risk," he said. While governments have tightened rules on many air pollutants over the decades, ultrafine particles have slipped through the cracks of policy, even as the science has grown more certain about their harm.
The McGill team didn't speculate about hypothetical futures. Instead, they took real emission reduction targets and climate plans already adopted by Toronto and Montreal—particularly ambitious goals around electric vehicle adoption—and modeled what would happen to ultrafine particle levels if those plans were actually executed. They then used established data on population health to estimate how many premature deaths could be averted. The most aggressive scenario they tested combined three elements: rapid adoption of electric vehicles (reaching roughly half the vehicle fleet by 2030 and nearly all vehicles by 2040), accelerated retirement of older heavy-duty diesel trucks (especially those built before 2007), and a reduction in overall traffic volume. Under that scenario, Montreal would see roughly 1,100 fewer premature deaths, while Toronto would prevent more than 2,500—a combined total exceeding 3,600 lives.
But the researchers also tested a more modest path. Even without a surge in electric vehicles, they found that simply keeping traffic levels steady and phasing out the oldest, dirtiest diesel trucks could still prevent over 3,300 deaths across both cities. That finding matters because it suggests meaningful progress doesn't require a complete transportation revolution—though the most ambitious scenario offers the greatest benefit.
Where those benefits land is crucial. Scott Weichenthal, a senior author and professor in McGill's School of Population and Global Health, emphasized that cleaner air would have its greatest impact in neighborhoods already bearing the heaviest pollution burden: areas with higher concentrations of low-income households, immigrant communities, and visible minorities. These neighborhoods tend to cluster near major roads and highways, meaning their residents inhale the worst air. A shift to cleaner transportation would thus narrow an existing health inequity, offering the most protection to those who have historically received the least. The study suggests that transportation policy is not merely an environmental question—it is a question of who gets to breathe clean air, and who does not.
Notable Quotes
Most Canadians are exposed to ultrafine particles on a daily basis and these pollutants are not currently regulated, despite growing evidence linking them to increased mortality risk.— Marshall Lloyd, Research Associate, McGill Department of Epidemiology and Biostatistics
Even without more electric vehicles on the road, keeping traffic levels steady and retiring older heavy-duty diesel trucks could still prevent over 3,300 ultrafine particle-related deaths across both cities.— Scott Weichenthal, Professor, McGill School of Population and Global Health
The Hearth Conversation Another angle on the story
Why haven't ultrafine particles been regulated if we've known they're harmful?
The science has been building for years, but regulation lags behind evidence. They're invisible, they're everywhere, and the sources are diffuse—every car produces them. It's easier to regulate a smokestack than the exhaust from millions of vehicles.
So this study is saying we could save 3,600 lives just by switching to electric vehicles?
Not just that. The biggest gains come from combining three things: more EVs, retiring the oldest diesel trucks, and reducing traffic overall. But even without the EV surge, just getting rid of the worst trucks saves over 3,300 lives.
That's a huge number. Why isn't this already happening?
Cost, mostly. Replacing vehicles is expensive. And the benefits—cleaner air, fewer deaths—they're spread across the whole population. The costs fall on specific people: truck owners, commuters, cities that have to invest in transit.
You mentioned the benefits would help low-income neighborhoods most. Why is that?
Because those neighborhoods are already next to the highways and major roads. They're breathing the worst air right now. Clean it up, and they benefit the most. It's a matter of geography and history—where cities built their poor neighborhoods.
So this is about justice as much as health?
Exactly. The study is saying that transportation policy isn't neutral. It either perpetuates an existing inequity or it fixes one.