Vehicle-related particulate matter (PM) emissions may arise from both exhaust and non-exhaust mechanisms, such as brake wear, tyre wear, and road pavement abrasion, each of which may be emitted directly and indirectly through resuspension of settled road dust. Several researchers have indicated that the proportion of PM2.5 attributable to vehicle traffic will increasingly come from non-exhaust sources. Currently, very little empirical data is available to characterise tyre and road wear particles (TRWP) in the PM2.5 fraction. As such, this study was undertaken to quantify TRWP in PM2.5 at roadside locations in urban centres including London, Tokyo and Los Angeles, where vehicle traffic is an important contributor to ambient air PM.

The sources of PM2.5 vary spatially with long-range transport sources generated mainly from secondary PM and local sources generated mainly from combustion processes associated with industrial operations and road transport. A recent literature review of various PM2.5 local source apportionment studies conducted in 51 different countries concluded that 25% of urban ambient air pollution from PM2.5 is contributed by traffic, 15% by industrial activities, 20% by domestic fuel burning, 22% from unspecified sources of human origin, and 18% from natural dust and salt. Both primary and secondary PM were accounted for in the analysis and the contribution was dependent on the source. For example, the researchers generally apportioned traffic sources by primary PM emissions and the unspecified sources of human origin based on secondary PM emissions. PM2.5 also varies spatially and temporally.

Over the last 20 years, environmental agencies worldwide have enacted regulations, including those for motor vehicles, in an effort to reduce the emissions of PM2.5; and, indeed, a decline is observable in areas with established monitoring networks. For example, in the US, from 2000 to 2016, the nationwide levels of PM2.5 have decreased 42%; with the vast majority of the measurements below the national standard of 12 μg/m3 since 2012. In Europe (EU-28), the emissions of primary PM2.5 decreased by 16% from 2003–2012.

Vehicle-related PM emissions may arise from both exhaust and non-exhaust mechanisms, such as brake wear, tyre wear, and road pavement abrasion. Several researchers have indicated that the proportion of vehicle traffic attributable to PM2.5 will come increasingly from non-exhaust sources, due to additional regulations limiting vehicle exhaust emissions. The current and future contributions of non-exhaust sources have been evaluated primarily through indirect methods such as various receptor-modelling approaches or air dispersion modelling paired with emission inventories. A recent literature review of non-exhaust emissions reported more than 250 estimates of contribution to ambient air PM.

When tyres interact with the roadway surface, tyre and road wear particles (TRWP) are produced, containing both the tread rubber and embedded road material.

The contribution of tyre wear to ambient PM10 and PM2.5 has been estimated to be between 0.8–8.5% and 1–10% by mass respectively, although the data are sparse and most estimates are indirectly calculated with only a few observational studies. Given the complex composition of the TRWP, a variety of analytical techniques have been proposed, but the only ones with sufficient specificity to the particles are chemical markers associated with the tread rubber, which include monomers styrene and 1,3-butadiene, as well as the dimers vinylcyclohexene and dipentene. Given the predicted increases in non-exhaust emission contributions to PM2.5, the current study was undertaken to measure levels of TRWP in PM2.5 in urban environments where traffic-related PM is significant. Sample locations were chosen to be representative of likely human exposure in various roadside microenvironments. To facilitate comparison to our earlier work and estimates published by others, we present mass-based concentrations and relative contribution to PM2.5 for both TRWP and tread for each sampling location.

Materials, methods

To select the cities for inclusion in this study, data were assembled for large urban areas in Europe, Asia, and the United States. A selection matrix was developed to identify cities based on several criteria including, levels of ambient PM2.5, traffic loads, population density, and local regulatory actions to reduce PM2.5.

In Europe, five cities were considered, including Barcelona, London, Milan, Paris and Rome, with London being ultimately selected. In Japan, six cities were considered, including Nagoya, Osaka, Tokyo, Saitama City, Yokohama, and Kyoto, with Tokyo being ultimately selected. In the US, three cities were considered, including Atlanta, Los Angeles and New York City, with Los Angeles ultimately selected.

Within each city, the site selection criteria included the presence of identifiable traffic and historical presence of high PM2.5 levels where possible. All air samples were collected near the roadside, and the distance from road was dictated by logistical constraints such as security of the equipment and available power sources. For London only, an urban background site was also included.

The analytical technique is based on the characteristic fragments generated by the thermal decomposition of the tyre tread polymers that include styrene butadiene rubber (SBR), butadiene rubber (BR) and natural rubber (NR). Briefly, the method consists of the following steps: the tread rubber polymers in environmental samples undergo thermal decomposition at 670 °C by Curie-point pyrolysis; next, the thermal decomposition products are separated using a gas chromatograph (GC); and finally, the pyrolysis fragments are quantified with mass spectrometry (MS).

The data were evaluated using the Analysis of Variance (ANOVA) and regression models to identify differences among the cities and trends in determinants of TRWP concentrations between sampling locations and cities.

Results

In total 80 samples were analysed, and the TRWP detection frequencies ranged from 0–100%. The lowest detection frequencies were recorded in Los Angeles, with four of the six locations showing no detections. The total ambient PM2.5 levels were low in Los Angeles during sampling days, which was surprising due to the historical levels recorded in the area for the same time of year.

The TRWP made a small contribution to total ambient PM2.5 levels, representing 0.1–0.68% of the total PM2.5 across all locations. The range of concentrations of TRWP were 0.012–0.29 μg/m3 in London, 0.010–0.1 μg/m3 in Tokyo, and 0.004–0.072 μg/m3 in Los Angeles. The highest concentrations were recorded at the Blackwall Tunnel Approach in London (mean 0.104 μg/m3 and range (0.03–0.29 μg/m3)) where significant braking activity occurs before the tunnel portal which creates more tyre wear abrasion than constant speed driving.

The highest TRWP PM2.5 concentration measured in Tokyo was at the Kawasaki Industrial Road location, which had the highest traffic count of the Tokyo sites. In both Tokyo and London, the traffic composition was dominated primarily by passenger car and light duty vehicle traffic, with truck traffic generally comprising less than 20% of the total traffic. One exception was Kawaskai Industrial Road, where the truck traffic accounted for nearly 43% of the traffic.

Uncertainties

The data generated from this research provide an initial observation of TRWP in PM2.5 using methods that are specific to tyre tread, however, they are site specific and may not be applicable more broadly given the small sample size and consequent low statistical power. The calculation of the TRWP concentration involves the assumption of 50% of the polymer in the tread and 50% of tread in the TRWP. However, the 50% assumption of tread in the TRWP is based on the characterisation of bulk TRWP in the size range of 0–150 μm. As such, the composition of the <10 μm fraction has not been specifically characterized.

It is currently unknown if the use of the 50% tread assumption overestimates or underestimates that composition in the <10 μm particles. Previously, the tyre wear contribution to the PM2.5 fraction was evaluated using Aerosol Time-of-Flight Mass Spectrometer (ATOFMS) and the researchers concluded that there was both a pavement and tread component, although the researchers did not have a quantitative estimate of the amounts. More recently, roadside airborne particulate in the 10–80 μm range was characterised using SEM EDX and the researchers concluded that the amount of pavement encrustation of the surface area of the ‘tyre core’ (i.e., tread) ranged from approximately 10% to more than 50%. As such, more research may be needed to refine TRWP composition in the PM10 and PM2.5 fractions.

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The Alliance for the Future of Tires (AZuR) has confirmed its participation as a cooperation partner for the tyre material flow for an interactive event on the Digital Product Passport (DPP), scheduled for 16 June 2026 at the Bottrop campus of Ruhr West University of Applied Sciences. With the European Union planning to introduce DPP from 2028, the initiative aims to establish greater transparency, resource conservation and functional material cycles. The upcoming gathering will focus on practical applications and future prospects for industry, trade, recycling and the circular economy.

The European Union has classified tyres as a priority product group under the new Ecodesign Regulation. The digital passport will provide accessible data on a tyre’s entire lifecycle, including material composition, carbon dioxide emissions, repair history, retreading suitability and recycling methods, potentially via QR codes or radio-frequency identification technology on the tyre itself.

Significant potential exists for the tyre recycling sector. Retreaders will be able to quickly assess casing history, mileage and past repairs to determine suitability for retreading. Recyclers will gain improved material transparency regarding ingredients, additives and recycled content, thereby facilitating both mechanical and chemical recycling. Thus, the passport can support longer tyre use and more efficient recovery of valuable raw materials.

AZuR views DPP as a key step towards advancing the tyre circular economy. Several manufacturers are already working on pilot projects, including Michelin’s coordination of a scalable system through the CIRPASS-2 project, standardisation efforts by Bridgestone and Michelin via the Global Data Service Organisation and AZuR partners’ work on radio-frequency identification and digital traceability. The upcoming university event offers companies, researchers and municipalities an early opportunity to address the passport’s requirements and develop practical solutions.

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Continental marked a major milestone on 22 May 2026 during opening ceremonies for the second expansion phase of its Rayong plant in Thailand. The development includes growth for the Passenger and Light Truck Tires division and the start of radial production for motorcycle tyres.

The Rayong motorcycle tyre facility operates with fully in-house manufacturing, from rubber compounds to finished products, using modern equipment. All processes adhere to Continental’s global quality and control standards, enabling production of both radial and diagonal tyres with capacity for future expansion. A high degree of automation and automatic monitoring systems eliminate manual errors while maintaining strict quality checks at every step.

Continental’s Rayong production serves diverse riding styles, including sport-touring and adventure touring segments, with popular radial and diagonal tyre models already in production. In March 2026, the plant received IATF certification, meeting international automotive standards that guarantee continuous quality processes and supply reliability for original-equipment customers.

The expansion also reflects Continental’s sustainability commitment, with solar energy supplying about 13 percent of the plant’s electricity needs. Additionally, the project has created new jobs, strengthening the regional economy.

Christoph Ettenhuber, Head of Business Field Motorcycle Tires, Continental, said, “By expanding our facility in Thailand, we are strategically strengthening our global production structure for Continental Motorcycle Tires. Together with our established operations in our Korbach plant in Germany, we are laying the groundwork for a faster, more flexible response to market demands. Rayong is a key component of our international motorcycle tyre strategy and underscores our clear commitment to growth and state-of-the-art production processes. For our customers, this means premium quality made by Continental – no matter which continent they’re on or which roads they travel."

Sahil Agrawal, Head of Manufacturing Operations in Rayong, said, “Quality is our top priority – for our original equipment customers as well as for end consumers. Our system captures every detail: all tyres are fully traceable at every production step. Online monitoring systems such as automatic scales, profilometers and camera systems ensure that every component is within specification limits. Automation – from the green tyre spray system to automatic tool management – enables us to achieve maximum quality levels while creating an ergonomic and safe working environment.”

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Bridgestone Corporation has once again been selected as a constituent of several globally recognised environmental, social and governance (ESG) indexes, including the Dow Jones Best-in-Class World Index, the FTSE4Good Index Series, the MSCI Selection Indexes, the FTSE JPX Blossom Japan Index, the FTSE JPX Blossom Japan Sector Relative Index, the MSCI Japan ESG Select Leaders Index and the MSCI Japan Equity ESG Select Leaders Index.

The Japanese tyre giant’s continued inclusion in these rankings serves as a concrete and objective embodiment of its corporate mission to serve society with superior quality. Company leadership views the ability to sustain such ESG initiatives over many years as a distinct organisational strength.

Regarding the Dow Jones indexes, Bridgestone has been selected for the Best-in-Class World Index for four consecutive years since 2022, which recognises the top 10 percent of sustainability leaders among 2,500 major global companies. The firm has also maintained a place in the Best-in-Class Asia Pacific Index for 16 straight years since 2010.

In the FTSE Russell assessments, Bridgestone has achieved eight consecutive years of selection for the FTSE4Good Index Series since 2018, alongside the same duration for the FTSE JPX Blossom Japan Index. The company has also been included in the FTSE JPX Blossom Japan Sector Relative Index for five consecutive years since 2021. For MSCI, Bridgestone has secured three straight years of selection for the MSCI Selection Indexes since 2023 while receiving the highest AAA rating in the MSCI ESG Ratings for three consecutive years.

The company has additionally earned high marks from the international non-profit CDP, receiving an A minus rating in both Climate Change and Water Security for 2025, marking six consecutive years at the leadership level. Bridgestone also obtained an A rating in the Supplier Engagement Rating for the seventh time. Key initiatives behind these recognitions include the expansion of its sustainability business model towards carbon neutrality and a circular economy, actions supporting nature positive goals such as sustainable natural rubber and water resource management, a comprehensive due diligence system based on Plan-Do-Check-Act cycles for human rights and environmental risk and global policy execution guidelines.

Bridgestone places sustainability at the core of its management, aiming to implement and evolve its unique business model across the entire value chain from production and use to renewal and raw materials. These efforts link business operations directly to the realisation of carbon neutrality, a circular economy and a nature positive world.

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Tegeta Green Planet and Shine Energy, both affiliated with Tegeta Holding, have launched a joint educational initiative to raise environmental awareness and a sense of responsibility among young people. The project addresses modern challenges such as environmental protection and sustainable development.

Company representatives are visiting schools across Tbilisi to hold informational meetings, presentations and workshops. The programme begins with presentations, followed by interactive games and activities designed to help students retain the information. At the end of each session, participants receive symbolic gifts and prizes as motivation.

Tegeta Green Planet focuses on teaching students the principles of specific waste management, including how to properly handle used tyres, batteries and oils. The sessions explain why proper waste management is essential for environmental protection and how it connects to the circular economy. Meanwhile, Shine Energy educates young people on the importance of energy, its everyday use and why developing renewable and sustainable energy resources is crucial.

The initiative is not limited to schools. In the near future, both organisations will expand their efforts to universities, aiming to broaden awareness about environmental protection, waste management and energy efficiency. The ultimate goal is to foster environmentally responsible attitudes among the younger generation, helping build a more sustainable and conscious society.

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