Capturing tyre pollution

Hear the phrase “vehicle emissions”, and you might instantly think of the exhaust. But tyre-wear accounts for nearly half of road transport air particulate emissions, and a student group at Imperial College London and the Royal College of Art have announced this week that they’ve made a device to capture bits of tyre that come off of cars, trucks and lorries during use. Chris Smith spoke to Masters student Hanson Cheng...

Hanson - Yeah, so there's actually half a million tons produced in Europe annually.

Chris - Just in Europe. So when you add to the rest of the rest of the world, it's going to be huge amount.

Hanson - It adds up. Tyre wear is actually the second largest microplastic pollutant after single use. Plastics and tyres wear off every time we accelerate, brake and turn a corner. And the particles are actually small enough to become airborne, which are linked to lung diseases, and the ones that make it into the waterways affect marine life as well as enter our food chain. While electric cars are great, and developments in renewable energy tailpipe emissions are projected to fall quite significantly, tyre wear will increase because of the heavier battery and torque of the car.

Chris - Yeah, that's a very good point. So basically, you know, as we move towards an electrified future, while we're dealing with one form of pollution, actually there's one very important one that's still there, like the elephant in the room and that is the wear particles of tyres. Have you got a solution that will work then?

Hanson - So we discovered that particles coming off tyres are charged due to friction with the road. So we created a device that captures particles using electrostatics, collecting them at source and preventing them from even entering our environment.

Chris - Why are they charged?

Hanson - From friction with the road surface.

Chris - So it's rather like rubbing a balloon on your head and then sticking it on the wall? You get some static electricity, the particles flying off the back of the tyre are charged in the same way.

Hanson - Yeah. So that's actually one of our first experiments. We took a sandpaper to a wheel, rubbed the balloon and saw that the particles jumped up and down. And so we built a test rig to test our initial idea and we explored different ways and geometries to maximize surface area to collect the particles. And we're currently at about 60% efficient.

Chris - Is this a bit like, you know how you have a mudguard on the back of the car that sort of dangles down and is there to cut down spray? Does it work in the same sort of way that you've got your trap deployed on that so that as the particles come up they have passing over that and it's charged and can attract them rather like iron filings are attracted to a magnet?

Hanson - Yeah. So our current device is attached on a wheel, and harnesses the spin at the wheel as well as its position, to take, and account for all the air flows around the wheel, to direct the particles into our device, and then electrostatics works to capture them.

Chris - And how effective is it? Do you know roughly what proportion of the particles that would otherwise end up in my lungs get caught?

Hanson - Currently in our test rig, we are capturing 60% of all airborne particles tested over one hour intervals, but the next steps would be to put our device on a car and see how it performs.

Chris - Why is it only 60%? I don't mean that in a disparaging way - 60% a lot better than nought percent, but why is there that 40% missing?

Hanson - A lot of that is just because of the position of the device. It needs to be as close as possible to the contact patch, but then you also have to be wary of hitting speed bumps and such, so we'll have to position further away than we want to.

Chris - And how does it hold onto the particles? Once it's got them in the first place, how do you make sure they don't fall off again?

Hanson - So once they're collected on the plates, we're using various cleaning mechanisms to gather them in a storage unit and then once they're in a storage unit that can be removed. These particles are actually small enough that they could be reused. So once we collect it, we can actually use it back into the manufacturing process of tyres as well as different applications or more creative applications such as extracting them for dyes and 3D printing.

Chris - What's the energy cost of doing this though? Is it going to add a lot of, effectively, miles to the gallon to a car if you were to deploy this?

Hanson - That is something that we're currently looking at. We're at the proof of concept stage and in our next prototypes we will consider more cost effective ways to develop a device that's more integrated.

Chris - And could you retrofit this? I know that you've got the electric car market in mind, but existing vehicles are a major headache with this. Could you retrofit to the existing road stock?

Hanson - Yeah, so we're looking into retrofitting them on buses just because they produce more per kilometre, basically from their weight, and they have a regular maintenance schedule that we could tap into to remove the cartridge and send it back to us.