Non-Exhaust Particulate Matter Emissions from Road Traffic
Summary
Non-exhaust particulate matter (PM) encompasses airborne particles generated by brake wear, tyre wear, road surface abrasion and the resuspension of deposited road dust. As tailpipe emissions decline through stricter regulations and vehicle electrification, the relative and absolute contribution of these sources to urban and roadside PM has grown. Non-exhaust PM spans a wide size spectrum from coarse particles (> 10 µm) to ultrafine nanoparticles (< 0.1 µm), each with distinct physicochemical properties and environmental fates. Compositionally, brake wear particles are rich in metals such as iron, copper and antimony, whereas tyre wear particles contain organic polymers, fillers and siliceous materials. Road surface abrasion contributes mineral dust, and resuspension mobilises a heterogeneous mixture of previously deposited pollutants. Collectively, these particles influence air quality, human respiratory health and climate forcing, and they pose a particular challenge for mitigation, as they originate from mechanical processes rather than fuel combustion. Current management strategies encompass material innovations for friction and tread compounds, enhanced street cleaning and policy measures to limit high-emission driving behaviours. A unified framework combining laboratory experimentation, field monitoring and source apportionment is essential to quantify emissions accurately and to develop effective controls.
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Non-Exhaust Particulate Matter Emissions from Road Traffic publication trend
The graph below shows the total number of articles in non-exhaust particulate matter emissions from road traffic across all publications each year (not limited to Nature Index journals).
Technical terms
Non-exhaust emissions: Particulate matter released from mechanical wear processes, distinct from exhaust tailpipe outputs.
PM10, PM2.5, PM0.1: Particle size fractions defined by aerodynamic diameter thresholds of 10 µm, 2.5 µm and 0.1 µm, respectively.
Brake wear particles (BWPs): Metallic-rich particulates generated by frictional abrasion of brake pads against rotors.
Tyre wear particles (TWPs): Polymer and filler fragments produced by the mechanical degradation of tyre treads on road surfaces.
Resuspension: Re-entrainment of road dust and deposited particles into the atmosphere by vehicle turbulence and wind.
Source apportionment: Analytical techniques used to quantify contributions of different emission sources to ambient PM concentrations.
References
- Beyond the tailpipe: Review of non-exhaust airborne nanoparticles from road vehicles. Eco-Environment & Health (2024).
- Automotive braking is a source of highly charged aerosol particles. Proceedings of the National Academy of Sciences of the United States of America (2024).
- A Review of Road Traffic-Derived Non-Exhaust Particles: Emissions, Physicochemical Characteristics, Health Risks, and Mitigation Measures. Environmental Science and Technology (2022).
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