Right now the environmental focus for new cars is CO2 emissions, one of the primary causes of climate change. We’re all being urged to go electric as soon as possible in a bid to reduce our environmental footprint and from 2030 the government has mandated that the only new cars we’ll be able to buy will be electric.
Assuming we’re all using green electricity by then, that’s job done for automotive then, isn’t it?
Well, think again. Electric cars still have emissions, it’s just that they’re not from the tailpipe.
Primarily there are two non-exhaust ‘emissions’ from cars and vans; rubber particles from tyres and brake dust.
Of course, there are other non-exhaust emissions such as lubricants and air conditioning losses. However, these are so small in volume that for the moment we need not worry about them.
Cars and tyres go together like bread and butter and from day one of cars being fitted with tyres they’ve always been made from rubber.
Rubber is great at giving compliance to the ride comfort and even better at keeping cars stuck to the road when cornering. But those qualities mean rubber also wears out, producing waste particles that are left on the road and then wash off the road and into the wider ecosystem. There is also evidence that the smallest of these particles can become airborne.
To give an idea about the scale of the problem, one scientific paper from September 2020 calculated tyre wear to be in the region of 0.2-5.5kg per person per year. Even at the lower end of this, that’s 13,600 tonnes of tyre wear in the UK.
Particles emitted by tyres are of mixed sizes, some are small enough to be airborne, classed as PM10 or PM2.5, that’s particles that are 10 or 2.5 micrometres in size. For reference, a micrometre is a thousandth of a millimetre.
The same scientific report stated: “A recent thorough risk assessment indicates the risk for human health via inhalation to be low, but no information is available on the risk caused by intake via the food chain. Data on degradation is scarce and most studies do not use realistic materials and conditions.
“The only published degradation study performed under environmental conditions implies a half-life of tyre rubber particles in soils of 16 months. For truck tyres, which mainly contain natural rubber, shorter periods were observed under optimum conditions in laboratory tests.”
With an increased focus from the population on plastics and rubber particles entering the environment, we all need to be aware of, and potentially aiming to reduce, the amounts they’re emitting.
One report last year, from vehicle testing firm Emissions Analytics, found that in the worst case tyres could emit up to 5.8g/km of rubber.
While school-level maths would suggest this is unbelievable – the average tyre weighs around 10kg which would mean it’s entire weight would be lost after just over 1,000 miles – Nick Molden, CEO of Emissions Analytics said: “The 5.8g per km figure is a worst case scenario. It was a fully laden car, on the cheapest tyres available at the time and the car was driven very hard.
“We’ve since done some more tests and found that on better tyres in normal conditions tyres can produce as little as 64 micrograms per km. It shows what can be done to reduce tyre particle emissions.
“The challenge to the industry and regulators is an almost complete black hole of consumer information, undone by frankly out of date regulations still preoccupied with exhaust emissions. In the short term, fitting higher quality tyres is one way to reduce these non-exhaust emissions and to always have tyres inflated to the correct level.
“Ultimately, though, the car industry may have to find ways to reduce vehicle weight too. What is without doubt on the horizon is much-needed regulation to combat this problem. Whether that leads to specific types of low emission, harder wearing tyres is not for us to say – but change has to come.”
Tyre manufacturers are aware of the issue and some, including Continental are already working with the US-based Tire Industry Project to research ways of addressing the issue.
The other area of non-exhaust emissions that still impacts electric vehicles is brake dust. It’s an area with ongoing research in the UK, although the US has already announced legislation to reduce the harmful copper particles that are emitted as brakes are worn.
Writing for the Medical Research council, scientist Dr Liza Selley, said: “Little is known of the impacts that non-exhaust particles have on respiratory health, but their small size and often metallic composition suggests that they could cause inflammatory airway injury.
“Brake dust is the most abundant non-exhaust particle, contributing up to 25% of total traffic particulates. This figure is forecast to increase as more people invest in electric vehicles so it is vital that we understand how the particles impact human health.”
Multi-national vehicle parts manufacturer Delphi which supplies brakes to both car makers at the factory as well as in the aftermarket has already moved to reduce the amount of copper in its brake pads.
“Every time you press the brake pedal, a small amount of copper is deposited onto the road. When it rains, this is washed into nearby streams and rivers,” a spokesman for the firm said.
“With millions of drivers using their brakes day in, day out, it is estimated that brake pads account for up to half of the copper entering water systems in urban areas. And with copper known to be very toxic to aquatic life, this can cause significant damage to the environment.
“When it comes to braking, copper is intrinsically difficult to replace, as it acts as both an abrasive and lubricant in the friction mix. Yet, we’ve re-engineered our entire friction formula to reduce copper content to no more than 0.5%. Better still, we’ve achieved all this without compromising on vehicle performance or safety - our new and improved formulation offers better fade performance and retains all its life, without compromising noise control or heat dissipation.”
For now, the message for drivers is to keep vehicles well-maintained and if there’s a choice when replacing components that wear to look for higher quality items if their focus is to be as green as possible. But like the upfront price of EVs, this isn’t necessarily the cheapest option.