When you hear the word “pollution,” most people associate it with things like factories, oil extraction plants, and vehicle exhausts. However, there is a hidden type of pollution that is not as widely known as it should be—one to which we’re even more directly exposed than exhaust gases. Surprisingly, this type of pollution can be produced by bicycles.
What are non-exhaust emissions?
Non-exhaust emissions mainly refer to the wearing down of vehicle brakes, tyres and road surfaces. Brakes are particularly relevant to ambient air pollution because they are a significant source of particulate matter, specifically PM10 and PM2.5 particles. On the other hand, tyres-release material tends to be larger in size and primarily affects water and soil bodies.
Why are non-exhaust emissions gaining more attention?
Non-exhaust emissions have drawn significant attention over the last ten years, partly due to the successful reduction of exhaust emissions through strict regulatory frameworks. In 2015, new vehicles in Europe started emitting equal or lower exhaust emissions compared to non-exhaust emissions. While non-exhaust emissions can be found in remote areas due to the long-range transport of particles, they are much more relevant in urban environments where more people live.
How can we reduce brake emissions?
Traditional grey cast iron brake discs, combined with European-type pads, emit the highest amounts of brake emissions. In contrast, drum brakes, due to their enclosed nature, emit only a fraction of the emissions of traditional grey cast iron disc brakes.
There are alternative brake pad formulations, such as non-asbestos organic pads, which are used in the US and Japan. These pads emit three to five times fewer emissions than their European counterparts. Additionally, regenerative braking has the potential to significantly reduce brake emissions because it minimises reliance on friction braking.
According to experts, the most effective way to reduce brake emissions is through fleet electrification. However, electrification comes with a challenge: heavier vehicles. Heavier electric vehicles tend to produce higher amounts of non-exhaust emissions from the tyres.
Nevertheless, when we consider the complete elimination of exhaust emissions with the adoption of electric vehicles and the fact that non-exhaust emissions are significantly reduced in modern systems, the increase in tyre emissions from EVs is not a major environmental concern. This is one of the reasons why electric cars and other low-emission vehicles are strongly promoted through policies in both the US and the European Union.
How are tyre and brake emissions affecting the environment?
For bicycles, the overall environmental benefits, combined with the positive impact on health, make non-exhaust emissions a negligible issue. However, when it comes to road traffic, non-exhaust emissions remain a significant environmental challenge.
Approximately 500,000 tonnes of tyre microplastics are released into the environment annually in the EU. Tires are the leading source of unintentional microplastic pollution, affecting air, soil, and water compartments, which in turn can cause ecosystem damage and biodiversity loss.
Unlike exhaust emissions, there are currently no epidemiological studies directly linking non-exhaust emissions to adverse human health effects. While numerous studies have been conducted, their results remain contradictory. We do know that brake particles are small enough to enter the human respiratory system and penetrate deep into the lungs. Additionally, the chemical composition of these particles includes potentially harmful elements such as heavy metals.
How are new regulations addressing non-exhaust emissions?
We are still in the process of understanding the full environmental implications of tyre microplastic emissions. More dedicated studies are needed to reach definitive conclusions. However, it’s not all bad news. Even though the specific health effects of these emissions are not yet fully understood, new regulations like Euro 7 will help tackle the challenges posed by non-exhaust emissions.
Outside Europe, similar regulatory efforts are emerging. The United Nations’ GTR 24 and Regulation 117 will serve as a foundation for addressing both brake and tyre emissions in Europe. These two regulations—the first of their kind—could serve as models for other regions worldwide in mitigating non-exhaust emissions.
To effectively reduce the environmental and health risks associated with non-exhaust emissions, it is not enough to simply implement policies that limit emissions at their source. We must also promote alternative modes of transport that generate less particle pollution in the first place. Prevention is always better than mitigation.
