The Air Beside a Busy Road Contains More Than Exhaust

 As tailpipe emissions decline, researchers are paying closer attention to particles released by tires, brakes and road surfaces.

Fine particles rising from tires and brakes on a busy urban road and drifting toward nearby homes.

                                                  AI-generated editorial illustration.

When we picture traffic pollution, we usually imagine a tailpipe.

But a moving vehicle releases particles even when nothing visible comes from its exhaust. Tires rub against pavement. Brake pads wear down. Road dust is crushed, disturbed and lifted back into the air.

Together, these sources are known as non-exhaust emissions. They come from gasoline, diesel, hybrid and electric vehicles alike.

The particles do not all remain beside the road. Some become airborne. Others settle onto streets, soil, waterways and buildings. A 2026 study in Australia found tire-related particles and chemicals in dust collected from urban balconies—evidence that road pollution can travel into residential spaces.

That does not tell us exactly how much people inhale or what health effects will follow. It does, however, challenge a familiar assumption: traffic pollution ends where the exhaust pipe disappears.

A tire is more than rubber

Modern tires are complex manufactured products. They contain natural and synthetic rubber, reinforcing materials, fillers and chemical additives designed to improve strength, flexibility and resistance to cracking.

As a tire rolls, accelerates, turns and brakes, friction removes tiny fragments from its surface. These fragments mix with pavement material and road dust. Some are large enough to settle quickly; smaller particles can remain suspended or be carried farther by wind.

One tire additive receiving particular attention is 6PPD. It helps protect rubber from degradation caused by ozone. When 6PPD reacts with ozone in the environment, it can form a transformation product called 6PPD-quinone, or 6PPD-Q.

The ecological evidence is already serious. 6PPD-Q is acutely toxic to coho salmon and some other fish. California has therefore required tire manufacturers to evaluate safer alternatives to 6PPD, while the U.S. Environmental Protection Agency is studying the chemical’s emissions, transport, ecological effects and possible management options.

For human health, however, important gaps remain. The EPA states that information about human-health effects is still limited. Detecting a chemical in dust is evidence of environmental presence—not proof that a particular exposure has caused disease.

Brakes create a different mixture

Brake wear produces another kind of traffic particle. Friction between pads and discs releases material containing metals and other components that vary with the brake-pad formulation.

In a 2025 laboratory study, researchers exposed models of human lung cells to fine particles from four kinds of brake pads. Particles from copper-enriched non-asbestos organic and ceramic pads produced some of the strongest signs of oxidative stress, inflammation and disruption of cellular processes. In that experimental system, their effects were greater than those produced by the diesel exhaust particles used for comparison.

This finding is important, but it should not be stretched beyond what the experiment showed. A cell study cannot tell us how many people will become ill, at what real-world exposure, or after how many years. It identifies biological signals that justify more research and better exposure measurement.

Electric vehicles change the problem—they do not erase it

Electric vehicles eliminate tailpipe pollution during driving, an important benefit for urban air quality. Regenerative braking can also reduce the use of conventional friction brakes in many driving conditions.

But electric vehicles still use tires and roads. Vehicle weight, acceleration, tire design, driving style and road surface can all influence wear. It is therefore misleading to describe any vehicle as producing no pollution at all.

This is not an argument against electrification. It is an argument for looking at the entire vehicle rather than only its engine.

Cleaner transport will require several changes at once: lower-emission power, safer tire chemistry, durable materials, lighter vehicles where practical, better public transportation and urban design that reduces unnecessary traffic.

What can individuals realistically do?

No individual can remove tire and brake particles from a city’s air. This is primarily a problem for manufacturers, transportation planners and regulators.

Still, a few actions can reduce avoidable wear:

  • keep tires correctly inflated;
  • avoid unnecessary hard acceleration and braking;
  • replace damaged or excessively worn tires;
  • walk, cycle or use public transportation when conditions make those options safe and practical;
  • avoid assuming that a closed window removes every form of traffic-related exposure.

People living near busy roads should not be made responsible for pollution they did not create. Better monitoring and product design matter more than personal perfection.

The disappearing tailpipe is not the end of the story

For decades, tailpipe emissions were the most visible symbol of traffic pollution. As engines and fuels become cleaner, the less visible sources become harder to ignore.

Tire wear, brake dust and resuspended road material form a complicated mixture. Some components have well-established ecological effects. Laboratory studies reveal mechanisms that may matter for the lungs. But direct evidence about long-term human exposure and health outcomes remains incomplete.

That uncertainty is not a reason for panic—and it is not a reason to look away.

The air beside a road contains a history of every vehicle that has passed: not only what it burned, but also what it left behind through friction and wear.

Educational information only; not individual medical advice.

Editorial disclosure: AI assistance was used in preparing and editing this article. The scientific claims and sources were reviewed before publication.

Sources

  1. Kaur S, et al. From Streets to Seats: Assessment of Tire Wear Particles and Tire Additive Chemicals in Australian Urban Dust. ACS ES&T Air. 2026. DOI: 10.1021/acsestair.6c00072
  2. University of Queensland. Microplastic tyre pollution found in Brisbane balcony dust
  3. U.S. Environmental Protection Agency. 6PPD-quinone
  4. U.S. Environmental Protection Agency. Where Rubber Meets the Road: EPA Researchers Study the Environmental and Health Impacts of Tires
  5. California Department of Toxic Substances Control. Motor Vehicle Tires Containing 6PPD
  6. Parkin J, et al. Copper-enriched automotive brake wear particles perturb human alveolar cellular homeostasis. Particle and Fibre Toxicology. 2025;22:4. Open article

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