Scientists learn more about the impacts of microscopic fragments of car and truck tires in the air we breathe, prompting calls to regulate non-exhaust emissions globally.

Any time you walk alongside a busy road, you’re inhaling pollution you cannot see. Thanks to decades of tightening regulations for new cars, exhaust (tailpipe) emissions are significantly cleaner than they once were. A recent study focused on US vehicle emissions found that rates of hydrocarbons, nitrogen oxides, and carbon monoxide all fell by more than 99% between 1957 and 2020. Car exhausts also produce a range of different types of particulate matter (PM) of different sizes – fine particles (PM_2.5) and coarse-but-still-small particles (PM₁₀) – comprised of soot, heavy metals, sulfates and nitrates. These too are managed through emission standards, to varying degrees, in most parts of the world.

But the same cannot be said for non-exhaust emissions, i.e. the PM produced from brake wear and tire abrasion. As of right now, these emissions – which together represent the majority of emissions from road transport – are completely unregulated. This will change in November 2026, when the EU becomes the first region in the world to directly target and set limits on non-exhaust emissions, via their Euro 7 emissions standards for cars and vans.

A cluster of recent scientific papers, drawing on research from Sweden, Germany, Italy, Slovakia, the UK Canada, and the US, paint a detailed and troubling picture of these invisible emissions, prompting calls for other regions to follow the EU’s lead in regulating them. So, let’s jump in.

How are they produced?

A standard vehicle disc brake consists of a rotor and pads. When you engage the brake pedal, these elements are pressed against each other, generating friction between them. This not only causes the pads and rotor to heat up, it also physically damages the surfaces; a combination that releases a mixture of tiny metallic filings, resins, and lubricants into the air around the brake assembly. These are brake wear particles and by some assessments, they account for 8–27% of total traffic-related emissions (by weight).

The size of the emitted particles depends on the composition of the brake pad and rotor, and the temperatures generated by the brakes. In general, the heavier the vehicle, and the more abruptly the brakes are engaged, the more particles are produced. Somewhere between 30 and 50% of all brake wear particles make their way into the air, with most of those airborne particles (80-98%) in the PM₁₀ size range.

Perhaps surprisingly, the mechanism behind tire abrasion wasn’t fully explained until 2024, in a paper from US researchers. Their models and experiments showed that tire particles are released through a fatigue fracture process. As tires roll along the road, cracks invisible to the naked eye form on the tire surface. Over time, these crack spread, detaching tiny particles of material (mostly PM₁₀-sized) from the tire, releasing them into the environment. The researchers also found that a threshold exists in tire performance – below it, wear rates are relatively low, but at or above it, tire wear accelerates dramatically. The threshold is related to the toughness of the tire, which means it is possible to measure it, and to design tougher tires using materials that produce lower emission rates. As with brakes, the heavier the vehicle, the worse the tire wear.

Something in the (urban) air

Scientists in Canada recently spent a year sampling the air across eight sites in the Greater Toronto Area – everything from quiet residential streets to a stretch of Highway 401, North America’s busiest road. In their paper, published last year, they showed that tire-related chemicals – not just ‘rubber’ – were present at every location they studied. A class of compounds called benzothiazoles, which are used as vulcanization agents in tire production, were found in 94% of samples, at concentrations highest close to busy roads. 6PPD-quinone is another key tire ingredient that was found at elevated concentrations at “traffic-impacted” locations. TMQ – an antioxidant for tires – was detected only near traffic. The researchers noted seasonal differences too, with the highest concentrations of tire-related chemicals measured in winter. This, they attribute to the use of more rigid winter tires, which are known to shed more tire wear particles than all-season tires.

A separate Toronto-focused study, from a group of Italian and Canadian environmental scientists, used a rather surprising sensor to detect non-exhaust emissions – a species of lichen called Evernia prunastri. Over a period of two summer months, the group exposed their lichen to the air at a variety of distances from Highway 401. They found a dramatic decrease in the concentration of tire particles as the lichen was moved further from the road. At 5 m away, they detected >17,500 particles per gram of lichen. At 150 m, that had dropped to 1,500 particles per gram, while the size of the particles remained pretty consistent throughout. In terms of brake wear particles, both antimony (a common brake ingredient) and magnetic susceptibility (a measure of the presence of metallic particles) both declined sharply – by 70% – within 35 m.

In 2023, researchers from Swedish National Road and Transport Research Institute concluded that tire wear particles were ubiquitous in urban areas. Their modelling-based study found the highest concentrations along busy highways and in poorly ventilated street canyons – where the street is flanked by tall buildings. In their 28 km × 34 km study area in central Stockholm, they estimated the total tire wear emissions (all particle sizes) amounted to 960 tonnes per year, compared to 51 tonnes of PM₁₀ exhaust emissions.

For a team of chemists from Leipzig, Germany, the focus was on presence of airborne micro- and nanoplastics in urban air, and the risks they pose to human health. Their study, published just last month found that tire wear particles from cars and trucks accounted for two-thirds (65%) of all of the plastic particles they detected in their experiment.

Their impact in our bodies

The Leipzig study estimated that residents inhale at least 2.1 micrograms of plastic per day (0.7 milligrams annually) through the air, with the majority of those particles fitting into the PM_2.5 size range. These fine particles have been shown to penetrate deeper into the respiratory system than coarse particles. As a result, the researchers say, city- dwellers face an increased risk of cardiopulmonary issues and lung cancer. The tire ingredients detected across sites in the Toronto study have also been linked to “acute toxicity, oxidative stress, and chronic respiratory and cardiovascular issues.”

A review paper published in June 2025 suggests that city dwellers “routinely inhale approximately 3200 tire wear particles daily”. It also claimed that fine particles are associated with 18-25% increased asthma incidence near high-traffic areas, and for every 10 µg m⁻³ increase in particle concentration, the risk of death due to cardiovascular issues grows by 12%. Tire wear particles have also been implicated in increased incidence of hypertension (which can lead to stroke and heart attack) in people living near major roadways. There has even been some evidence that the ability of tire wear nanoparticles to cross the placental barrier may come with developmental and reproductive risks.

There are no positive outcomes to having tire- and brake-wear particles in the air we breathe.

What can we do?

The first thing that would make a significant difference would be to have fewer vehicles on the road in general, and for those vehicles to be lighter than they are today. As I’ve written about previously, car bloat and the popularity of ‘supersized’ cars are a major issue for our cities.

And while electrifying every car, van and truck on our roads would greatly improve air quality in general, it wouldn’t necessarily alleviate non-exhaust emissions. Thanks to their battery packs, electric vehicles are generally – but not always – heavier than their fossil-fuel equivalents, which means that they’re more susceptible to tire wear. The Stockholm modelling study suggested that if all light vehicles on Stockholm’s roads suddenly transformed into electric vehicles, tire wear particle concentrations in the city would increase by 13%. Interestingly, it might be a different situation for brake wear because EVs use regenerative braking. Chinese researchers found that under continuous braking, EVs produce three times fewer brake wear particles than gasoline cars.

The automotive industry – prompted by the introduction of the EU’s Euro 7 emissions standards – is changing the way it makes and tests brakes and tires. New brake disc materials, coatings and designs are all in development with some previously ‘high end’ braking systems being adopted more widely. The tire industry is focusing on developing tougher tire formulations, as well as developing new assembly techniques and testing facilities. As part of Euro 7, tires in Europe will be labelled with their abrasion performance. Car makers are also looking to increase the use of lightweight materials in vehicle interiors. The hope is that all of these improvements will be gradually rolled out beyond the EU.

At an individual level, car owners could drastically reduce non-exhaust emissions simply by driving better – avoiding rapid acceleration and hard cornering, anticipating stops and using gentle braking to slow down. Maintenance too makes a difference, so be sure to keep tires at the appropriate pressure, and don’t carry heavy objects unnecessarily.

All pedestrians can really do is avoid exposure. Try to maximize distance from the road itself – as we’ve seen, these emissions are worst closest to the traffic. So, even when crossing the road, be sure to step back from the edge of the path. Where traffic is unavoidable (e.g. for cyclists or for those living with chronic health conditions), consider wearing a tight-fitting FFP2 mask – as the BBC reported in February, respiratory protection in high-traffic areas leads to less air pollution getting into the blood.

And of course, no matter how we travel, we can talk to our representatives (local and national) about this form of pollution, and lobby for policies similar to those being introduced in the EU.