The debate around vehicle-generated non-exhaust emissions took turn this week when research undertaken by the University of Southampton found that particulate matter from copper-enriched brake pads is more hazardous to health than that from a diesel engine.
Non-exhaust emissions are generally taken to mean tyre wear particles (TWPs) brake wear particles (BWPs) and the resuspension of particles on the road.
As legislation and technological progress has reduced the emissions from vehicles’ exhaust, many countries are now finding that non-exhaust emissions contribute more by mass than exhaust emissions.
Brake wear particles are troublesome because they are chemically much more complex than those from exhausts or tyre wear and there are four different classes of brake pad design in current use:
- Low-metallic (LowM)
- Semi-metallic (SemiM)
- Non-asbestos organic (NAO)
- Ceramic
The team collected particles from all four and tested their effect on lung function compared to diesel exhaust particles.
Lead author of the study, Dr James Parkin, explains that a move to electric cars is bringing the problem into sharper focus: ‘We wanted to understand how different types of chemical composition of pads affect the toxicity of the particles emitted and what this might mean for the health of individuals.’
They found that of the four types of brake pads, non-asbestos organic pads had the worst impact on lung cells in the laboratory, proving more detrimental to them than diesel exhaust particles.
In the US, NAO brake pads are the most popular type of brake pad in use, preferred because of their low cost, low noise and longevity. The pads were introduced to replace a design which contained asbestos. The asbestos provided thermal conductivity and to replicate that, the NAO pads featured copper fibres.
The second worse performing pads were the ceramic ones, which also contain high amounts of copper. When the amount of copper was reduced in further experiments, the particulate matter became less toxic.
Project supervisor Professor Matthew Loxham said: ‘This research has important implications for health and future policy because as we switch from diesel and petrol-powered cars to electric vehicles, non-exhaust particle emissions will remain. Non-exhaust emissions could increase over time due to electric vehicles being heavier than combustion engine vehicles and creating greater friction.’
In conclusion ,the team suggest that: ‘current legislation, which focuses on PM exhaust emissions, may be inadequate to mitigate the health effects of vehicle-derived PM, and that regulations also need to target not only non-exhaust PM emissions, but also specific components of PM.’
Sarah Sleet, chief executive at Asthma + Lung UK said: ‘It’s encouraging to see new research into the causes and impact of air pollution, which is a health emergency and contributes to up to 43,000 premature deaths a year in the UK.
‘What’s novel about this study is it examines different types of brake pads and assesses which materials might be most damaging, but all sources of pollution from traffic must be reduced to protect people’s health. The government needs to restrict the number of cars on the road and commit to an ambitious Clean Air Act which could protect people, wherever they live, from the dangers of polluted air.’
The full research can be read here.
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