Every other Friday, the Outside/In team answers one listener question about the natural world.
This week's question comes from Beth Anne in Montana.
"How much toxic airborne pollution is contributed by vehicle tires? Even if we electrified all transportation overnight, how much would tires continue to contribute to toxins in the air?”
Producer Marina Henke hit the metaphorical road to find out.
Marina Henke: Quick story. Cars used to belch black smoke. In the 1940s, smog in cities like Los Angeles was so bad, that fields of produce could wither over the course of a day. But then, came the regulations. Today, things aren’t perfect, but tailpipe emissions are a fraction of what they used to be. So, scientists started wondering about other parts of our cars that could be causing pollution. Like… our tires and brakes.
Heejung Jung: It has been there, but it became much more important because other sources have reduced its emissions substantially.
Marina Henke: That’s Heejung Jung, a professor of mechanical engineering at University of California Riverside. He studies how cars contribute to air pollution. Heejung told me that these days, the pollution from our tires and brakes can rival tailpipe emissions. The physics of this is pretty simple. When we drive, the friction between the car and the road wears down our tires. During its typical lifespan, a tire will actually lose between 10 to 20% of its mass this way. Basically, it turns to tire dust, which is a weird mix of a lot of chemicals: rubbers, hydrocarbons, heavy metals. The exact recipe of tire brands vary and are actually proprietary information, so it’s hard to know what’s in them.
Marina Henke: But no matter what, anytime this kind of cocktail of particles is entering the air, scientists take note. Exposure to particulate pollution has been linked to asthma, cancer and Alzheimers. A few years ago, Heejung and his team took to the streets to study just how much of that tire dust was making it into the air that we breathe.
Heejung Jung: The further you live away from major roadways, such as highways, the less you are exposed to. So that's good news and bad news, because depending on where you live, you can be much more exposed to or much less exposed to brake and tire wear particles.
Marina Henke: Brake and tire wear particles don’t go far once they’re in the air, Heejung explained. For the most part they stay right around the road. And the risk to human health?
Heejung Jung: Not much human subject or animal study has been done to figure out how much toxicity the tire particles are affecting us.
Marina Henke: We don’t really know yet. But we do know that tire particles are a significant source of microplastics in the ocean. And, they pollute freshwater streams too.
News anchor clip: New this morning, the science is clear, a chemical from tire dust is killing massive amounts of Coho salmon in the Pacific Northwest…
Marina Henke: A few years ago, a group of scientists researching salmon die-offs in the Pacific Northwest found the culprit: A common tire additive known as 66PD. It reacts with ozone and creates a new chemical that’s lethal to the fish.
Rep. Katie Porter clip: The salmon suffocate as their blood thickens, they flail near the surface in futile effects to get oxygen before sinking to the bottom where they die en masse…
Marina Henke: This is a Congressional hearing in 2021, where scientists pushed Congress to support alternatives to 66PD. Now, our listener also asked whether tire pollution is a problem with electric vehicles, too. Unfortunately, there’s actually a good chance EV cars are worse for this problem.
Heejung Jung: Those vehicles are heavier compared to conventional internal combustion engine vehicles and heavier vehicles make more friction, so it generates more brake and tire wear emissions.
Marina Henke: Now, Heejung doesn’t think that’s a strike against all EVs, but that it is an important design question.
Heejung Jung: So my take is let's promote smaller, lighter electric vehicles as opposed to heavier and larger electric vehicles.
Marina Henke: Heejung and his colleagues are hoping that research like theirs can help shape future regulations. He thinks, if tailpipe emissions are so well regulated, maybe it’s time that tire emissions are, too.
If you’d like to submit a question to the Outside/In team, you can record it as a voice memo on your smartphone and send it to outsidein@nhpr.org. You can also leave a message on our hotline, 1-844-GO-OTTER.
