‘Non-exhaust' emissions are the next green target

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The year is 2030. The roads are filled with the quiet buzz of electric vehicles and the population is filled with a quiet sense of satisfaction that the worst of our traffic pollution problems have been consigned to the history books.

Except they haven't.

According to the research group, Emissions Analytics, pollution from tyre wear can be 1,000 times worse than the stuff that comes out of a car's exhaust.

Harmful particles from tyres – and also brakes – is a very serious and growing environmental problem. It's also one that we are making worse in many ways. The increasing popularity of big, heavy vehicles such as SUVs, and growing demand for electric vehicles, which are heavier than standard cars because of their batteries, is actually increasing the amount of particle pollution produced on the roads.

Lack of rules for non-exhaust emissions

Unlike exhaust emissions which have been rapidly reduced by car makers thanks to the pressure placed on them by European emissions standards, there are no rules and regulations covering ‘non-exhaust' emissions. Non-exhaust emissions (NEE) are particles released into the air from brake wear, tyre wear, road surface wear and the spreading of road dust as vehicles travel around. No legislation is in place to limit or reduce NEE despite the impact they have on air quality.

To put that into some sort of context, Emissions Analytics performed some tyre wear testing.

Using a regular family hatchback running on brand new, correctly inflated tyres, it was found that the car emitted 5.8 grams of particles per kilometre. That doesn't sound very much until you consider all those exhaust emissions we've been worried about only account for 4.5 milligrams per kilometre. A slightly rougher road surface, incorrectly inflated tyres, and even the use of budget tyres, can all have the effect of pushing that number up even higher.

Audi is working on filter traps

There is work being done to counter the particle pollution though, and Audi has been busy designing something other than a car to help tackle the issue.

Tyre and road wear particles are generated as a result of every car ride. In Germany alone, an estimated 110,000 metric tonnes of it ends up on the streets in the form of microplastics. From there, it is blown into the environment by the wind, or is washed by the rain through the sewers into the soil and rivers, and ultimately the oceans.

The Audi Environmental Foundation, in conjunction with the Technical University of Berlin, has developed new filters for urban run-off. They prevent tyre particles and other environmentally harmful substances from being washed into sewers and bodies of water along with the rainwater. In real world tests, the filters managed to permanently trap regular street cleaning waste, cigarette filters, microplastics up to three millimetres in size, sweet wrappers, and lids from disposable coffee cups.




The picture shows the possible module combinations of the urban filter: depending on the catchment area, different filters are required to filter the floating, suspended and sedimentable particles from the water. The filters contribute to a continuous improvement of the water quality and relieve rivers and lakes.

That's obviously a solution for the future, but in the meantime it's important to remember that not all the traffic pollution we should be worried about is conveniently channelled through your exhaust. Obviously you can't do without tyres and brakes, but you can help a little by making the right choices.

Until Audi and the rest of the scientific and automotive industry comes up with a solution that can be rolled out in bulk, microplastics will remain a pollution issue. In the meantime, make sure your tyres are properly inflated, and as far as you can, make sure you get the best quality tyres you can afford.

And well done if you already drive an EV, but it's still worth bearing in mind that you can help the environment by using regenerative braking as much as possible, thereby prevent brake dust contaminating the environment.

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