Widespread misunderstanding exists about how airborne tyre emissions contribute to air pollution, photo courtesy Siriel Saladin
Widespread misunderstandings about the contribution of tyre wear to air pollution have crept into government reports in the UK, EU and US and could wrongly influence critical policy decisions.
A study published yesterday in Environmental Science & Technology Letters, reveals decades of misunderstandings about how much vehicle tyres contribute to air pollution.
The study, by researchers in the Yusuf Hamied Department of Chemistry and the Department of Engineering at the University of Cambridge, warns that since 1995 the models used by scientists and environmental agencies have overestimated the contribution of tyre particles to air pollution. Because these emission models will be used for upcoming Euro 7 standards, it is critical that tyre emissions are accurately represented.
Airborne tyre wear is often linked to the increased weight of electric vehicles, which has raised concerns that shifting to electric cars may not reduce air pollution. However, this new study suggests that the contribution from electric vehicles to air pollution could be lower than anticipated.
Accidental misunderstandings
First author Siriel Saladin holds a German PhD thesis from 1998 which is one of the primary sources that has been misinterpreted.
The discrepancy between the existing models and the current state of science is based on inaccurate interpretation of published research due to unclear terminology, misquotations and language barriers.
“After analysing more than 100 citations, we have found more inaccurately than accurately quoted primary research,” said the study’s first author Siriel Saladin, a second-year PhD student in Professor Chiara Giorio’s atmospheric research group.
Inaccuracies included confusion with terminology, unit mix-ups and misquotations.
Examples found by the researchers include statements which confuse road wear with tyre wear, and quotation figures per tyre rather than per car.
“These mix-ups have created an ‘illusion of truth’ around high emissions of airborne tyre particles. However, most primary sources suggest that the mass of airborne particles emitted by tyre/road interaction is mainly from the road and not tyres,” said Saladin.
Willingness to correct
“I have been heartened by how the community has been willing to acknowledge where errors have been made and the willingness to correct them. Based on the nature of the misquotations, we strongly believe they happened unintentionally,” emphasised co-author Professor Adam Boies of the Department of Engineering.
“We trust academia and governments and we believe everyone acted to the best of their knowledge. When we reached out to scientists and agencies we found a genuine support and a shared commitment to truth,” said Professor Giorio.
Accurate figures needed
The researchers emphasise that the actual amount of airborne tyre emissions remains the subject of scientific discussions.
It is also unknown whether non-airborne particles released by tyres, which pollute water and soil, could degrade over time and contribute to air pollution.
“The main point is that currently accepted mass-based emission factors for directly emitted airborne tyre wear particles need revisiting to ensure that what is being included within emissions models represents the best science we have to date,” said Professor Boies.
"Scientific truths are sometimes more intricate than they initially appear. It is vital that the scientific community engages in evidence-based discussions, taking into account new findings and ultimately providing more accurate figures for research and policy," stated Professor Giorio. "We’re confident that this correction will happen."