Search Results (113)

Non-exhaust emissions (NEEs), particularly brake wear particles (BWPs), have become a dominant source of traffic-related particulate matter (PM), accounting for approximately 77% of PM10 and 60% of PM2.5 emissions. Accurate quantification of these emissions is essential under increasingly stringent regulations such as Euro 7. However, measurement reliability is strongly influenced by particle transport and sampling losses. This review provides a state-of-the-art analysis of laboratory-scale methodologies for investigating BWP emissions, focusing on pin-on-disc (PoD) tribometers and inertia dynamometer systems. Particular attention is given to chamber design, airflow management, sampling configurations, and the mechanisms governing particle transport efficiency. The literature indicates that PoD systems are often affected by complex and non-uniform flow fields, leading to incomplete particle capture and reduced representativeness, whereas inertia dynamometers, especially when coupled with constant volume sampling (CVS), provide more controlled and reproducible conditions. Key loss mechanisms, including inertial deposition, diffusion, gravitational settling, and non-isokinetic sampling effects, are major contributors to uncertainty. The reviewed studies highlight that aerodynamic limitations in PoD systems, particularly box-shaped chambers, promote flow recirculation and particle losses. Advanced optimization approaches that combine artificial neural networks (ANNs) with computational fluid dynamics (CFD) simulations show strong potential to improve system design and measurement reliability. Full article

Non-exhaust emissions represent a growing share of traffic-related particulate matter and are increasingly addressed by regulatory frameworks. This study presents a comparison of two brake emission test cycles, the California Brake Dynamometer Cycle (CBDC) and Worldwide Harmonized Light Vehicles Test Procedure Braking Cycle (WLTP-BC), the latter being formally embedded in current regulations. Firstly, we present a detailed comparison of WLTP-BC and CBDC in terms of parameters that are shown to affect or may affect braking control and particle emissions (braking torque, vehicle speed, acceleration, friction work, disc temperature, etc.). Secondly, we present a way to evaluate test system torque control quality, supplementing the friction work-based method present in United Nations Regulation (UNR) No. 179, and quantitatively assess the control quality between the cycles. CBDC was found to be the more challenging cycle to execute. However, the testbench control architecture was found to be sufficient to execute it with high fidelity. Thirdly, we present the emission results obtained from the cycles, both per kilometre driven, as well as per friction work done. We argue that the latter is better for comparing the emission results obtained from cycles with different braking profiles. Driving the CBDC resulted in higher particle mass (PM) emissions but similar particle number (PN) emissions. In light of this dataset, friction work seems to be a better predictor for PN than for PM. While this study encompasses only a single friction pair, and more tests with different brakes would be required to generalize the findings, the results highlight the importance of cycle selection in emission research, both in terms of quantifying the emissions and demands for the test system. Full article

Brake wear is a major contributor to non-exhaust particulate emissions, and standardized measurement methods are currently being extended from light-duty (LD) to heavy-duty (HD) vehicles. However, differences in brake geometry and operating conditions may influence particle transport and sampling representativeness in HD brake emission test systems. This study investigates the influence of brake caliper position on particle emissions and mixing uniformity in an HD brake emission test setup. Experiments were conducted using a dynamometer-based system with four sampling probes distributed across the sampling plane. Emissions of particulate mass (PM10, PM2.5) and particle number (solid and total particle number emissions for particles >10 nm) were measured for two caliper orientations (horizontal and vertical). Mixing quality was assessed by comparing probe-specific emission results to the plane-averaged value. The results show that the vertical orientation was associated with 34% higher PM10 and 40% higher PM2.5 emissions on average, a significant increase. Particle number emissions also increased on average, but the differences were small relative to test repeatability. The more pronounced effect on PM suggests that the caliper position mainly influences the transport and losses of larger particles, which contribute more to PM. In contrast, the uniformity of particle concentration across the sampling plane was similar for both configurations, with deviations comparable to those reported for LD systems. These findings should be considered in the interpretation of results obtained with any similar test systems, comparisons between such systems, and literary reviews. Full article

With the progressive decline of tailpipe emissions, non-exhaust sources such as brake wear are becoming an increasingly important contributor to traffic-related particulate matter in urban environments. In this context, improving real-world characterization of brake wear particles is essential for air-pollution assessment, source apportionment, and the development of cleaner and more sustainable road transport systems. Here, we investigated the emissions levels, particle size distribution and elemental composition of particles released during harsh real-world braking events by a single light-duty vehicle braking system equipped with an original manufacturer (OEM) non-asbestos organic (NAO) pad formulation. Using a direct on-vehicle sampling system combined with real-time particle sizing and high-resolution microscopy, we observed that particle emissions remained close to background levels at speeds up to 100 km/h, but rose sharply at 120 km/h, reaching 3.7 × 10⁷ #/cm³ in the 8–10 nm size range. This increase suggests that higher speeds are associated with elevated particle emissions, likely due to the higher braking temperatures reached at increased vehicle speeds. The emitted particles were mainly spherical agglomerates rich in iron, titanium, barium, zirconium, and sulphur, consistent with NAO pad formulations. Our results show that the investigated NAO pad system can deteriorate under thermal stress, potentially leading to higher levels of nanoparticle emissions compared to low-metallic or semi-metallic pads investigated under similar conditions. These findings provide real-world evidence relevant to urban air quality research, support the refinement of non-exhaust emissions inventories, and highlight the importance of thermally resilient friction-material formulations for mitigating residual particulate emissions in increasingly cleaner transport systems. Full article

The European Union is currently focused on reducing non-exhaust emissions (NEE), a growing source of particulate matter (PM) pollution from road transport. This study presents the Life Cycle Assessment (LCA) of an innovative zero-emission magneto-rheological braking system specifically designed to meet new brake emission targets. Prototyped for A-segment passenger cars, the system uses magnetorheological fluids that modify their rheological properties when subjected to an external magnetic field. The environmental impacts of this innovative system are compared with those of a conventional disc brake, considering 16 environmental indicators across all life stages: raw material extraction, manufacturing, use, and end-of-life. In fact, although the system eliminates PM emissions during operation, it is crucial to assess whether it remains advantageous in terms of overall environmental impacts when the full life cycle is considered. As a prototype, this study also aims to inform design improvements that minimize environmental burdens. Results show that the innovative braking system performs better, particularly during the use and maintenance phases. Moreover, several eco-design strategies have been identified to reduce impacts related to materials and production. Overall, the magneto-rheological system demonstrates strong potential to meet future emission standards while improving the sustainability of vehicle braking technology. Full article

Non-exhaust particulate emissions are expected to remain a relevant source of traffic-related air pollution, including an increase in electrified vehicle fleets. Particle formation results from tribological interactions and is influenced by both operating conditions and friction material system. This study presents an extended measurement methodology under application-relevant tribological conditions for the reproducible quantification of PM₁₀ and PM_2.5 emissions from dry-running friction systems and applies it to a systematic investigation of operating parameter and friction pairing effects. A dry inertial brake test bench with an enclosed friction chamber and integrated aerosol measurement chain was used under controlled tribologically relevant conditions. Specific friction work and specific friction power were varied by adjusting sliding velocity, contact pressure, and inertial load. Six friction pairings, comprising four representative friction lining types combined with either C45 cast steel or GGG40 gray cast iron, were examined. In situ PM₁₀ and PM_2.5 measurements were complemented by gravimetric wear and microstructural analyses. The results show that specific friction work has a direct influence on PM₁₀ and PM_2.5 emissions, whereas the independent effect of contact pressure is secondary. Friction power exhibits material-dependent effects. Emissions also vary strongly with friction pairing, indicating that operating conditions and material system must be considered jointly when assessing low-emission brake systems. Full article

Electric vehicles (EVs) have emerged as a vital component of sustainable urban mobility. In this life cycle assessment, the GREET model (Greenhouse Gases, Regulated Emissions, and Energy Use in Technologies) is used to compare three EV scenarios for Washington, DC, the capital of the United States. We compare these three scenarios to a 2022 baseline scenario that describes the current state of EV utilization in Washington, DC. The three future scenarios we examine are based on policy assumptions that differ in the extent to which they integrate renewable energy into the EV future of Washington, DC. Our findings suggest a significant decrease in greenhouse gases between 52 and 66 percent by 2050 and a similar decline in other air-pollutants associated with all three future scenarios. This confirms the advantages of EVs for urban air quality. However, two important aspects of the analysis suggest that there is (1) the threat of emissions leakage associated with electricity imports into DC, which complicates the overall assessment of local environmental benefits; and (2) an increase in non-exhaust emissions of particulate matter attributable to tire and brake wear. These emissions cannot be removed through electrification and tend to increase due to the increased weight of EVs. Our analysis shows that the full capabilities of electric vehicles can best be realized through grid decarbonatization. Achieving genuine sustainable mobility therefore requires complementary strategies that address transboundary emissions and vehicle-specific non-exhaust particulates. Full article

Urban transport is a major contributor to particulate matter (PM) pollution, yet information on the spatial distribution of fine and ultrafine particle fractions remains limited in medium-sized tropical cities. This study examines the spatial variability of transport-related particulate matter across eleven urban districts in Padang, Indonesia, using Nano Sampler-based measurements. Size-segregated PM concentrations (PM₁₀, PM_2.5, PM₁, and PM_0.5) were obtained from 24 h sampling campaigns conducted between June and July 2025 at locations selected based on urban density, proximity to major roadways, and land-use characteristics. Descriptive statistics, correlation analysis, and principal component analysis were applied to evaluate spatial patterns and traffic-related influences. The results show pronounced spatial heterogeneity in PM concentrations. Traffic-intensive and mixed-use districts exhibited higher PM levels, particularly for coarse and ultrafine fractions, whereas coastal districts showed lower concentrations due to enhanced atmospheric ventilation. Strong correlations were observed between traffic volume and coarse PM fractions, with moderate associations for fine and ultrafine particles, indicating combined exhaust and non-exhaust emissions. These findings highlight the importance of district-specific mitigation strategies and size-resolved monitoring to support effective urban air-quality management. Full article

Although the organic fraction of PM_2.5 has been extensively studied, there is a considerable gap in understanding the organic fraction of coarse particles with diameters between 2.5 and 10 µm. We investigate the composition of coarse organic aerosol (OA) across rural, suburban, and urban areas of Switzerland. Using Aerosol Mass Spectrometer analyses of water-soluble OA extracted from collected filter samples (one entire year, 441 samples per size fraction), we identified two distinct classes of coarse OA. The first class, which constitutes 41–81% of coarse organic carbon (OC), is associated with primary biological organic carbon (PBOC). PBOC is characterized by specific marker ions (e.g., C₂H₅O₂⁺) and exhibits pronounced seasonal variation, with peak concentrations observed in the summer. This seasonal trend correlates with that of molecular markers such as arabitol and mannitol, as well as the fraction of biological particles determined by automated scanning electron microscopy coupled to energy dispersive X-ray spectroscopy of individual particles. The second class, contributing 7.9–17.8% to OC_coarse, is denoted as sulfur-containing organic carbon (SCOC) due to the presence of sulfur-containing ions such as CH₃SO₂⁺. Elevated concentrations of SCOC in urban environments near roadways suggest a strong influence from non-exhaust traffic emissions and resuspended dust. While the overall variation in coarse OC between rural and urban areas is approximately 10%, PBOC concentrations are 1.4 times higher in rural areas, whereas SCOC concentrations are 1.5 times higher in urban settings. Overall, our study shows that although OC_coarse concentrations in Switzerland are relatively consistent across site types, major water-soluble sources, particle properties and composition vary considerably geographically and seasonally. Full article

The contribution of non-exhaust emissions (NEEs) to particle number concentration (PNC) remains insufficiently quantified, particularly across different urban environments. In this study, we address this gap by quantifying the contribution of NEEs to airborne nanoparticles in urban areas. Using positive matrix factorisation (PMF), conditional probability function analysis, Pearson correlation, and source identification, we identified five source factors contributing to PNC at two sites in London: a traffic site and a background site. Five source factors were resolved at both sites: Aitken-mode traffic exhaust particles, nucleation-mode exhaust emission, secondary aerosol, non-exhaust emission, and regional background accumulation. Interestingly, the contribution of NEEs differed between the two sites. At the traffic site, NEEs contributed 14.9%, while at the background site, their contribution was higher at 28.5%, likely due to the favourable summer dispersion conditions. However, the contribution of nucleation-mode exhaust emission also showed significant differences: 26.6% at the traffic site and only 9.9% at the background site. Based on these findings, we propose that air quality policies should integrate NEEs into regulations, improve road maintenance, and use PNC-based along with metal tracers to identify and control PNC. This study offers valuable insights for developing strategies to manage urban nanoparticle pollution. Full article

Brake dust (BD) generated by vehicle braking systems, including those of cars and trains, contains various Potentially Toxic Elements (PTEs) that may pose risks to human health and the environment, particularly in soils where it accumulates. This study aims to evaluate differences in the chemical composition of BD emitted by road and railway transport, to analyze its deposition mechanisms in soil, and to estimate the associated carcinogenic (CR) and non-carcinogenic (HQ) risks from ingestion and dermal exposure. Two sites were selected: one adjacent to a busy roadway and the other near a railway line. At both locations, soil-sampling transects were established perpendicular to the emission sources at distances of 3, 6, 15, 25, and 45 m. Elemental concentration analyses were integrated with magnetic measurements, which are selective for magnetic iron oxide particles. The results confirm elevated concentrations of several metals at both sites. Both elemental and magnetic data reveal a clear deposition gradient, with the highest accumulation within 15 m of the source, followed by a gradual stabilization up to 45 m. However, the railway site exhibited significantly higher concentrations than the road site, highlighting the relevance of non-exhaust emissions (NEEs) from railway traffic, which remain poorly investigated. While HQ was non-significant, CR associated with Pb-, Ni-, and As-rich BD exceeded acceptable threshold values, particularly for ingestion exposure at the railway site. These results highlight the significance of NEEs from rail traffic in terms of soil contamination and risk assessment. Full article

This study quantifies energy consumption and tank-to-wheel (TTW) emissions of urban buses under varying traffic conditions and passenger loads in Osnabrück, Germany, to support emission-aware route assessment in sustainable mobility applications. Exemplary bus trajectories were modeled on a representative 6.17 km route of line M5 (18 m articulated bus; diesel and battery-electric) within a 22.31 km² traffic net using the Simulation of Urban MObility (SUMO) software, and were calibrated with traffic sensor data. To assess the influence of trajectories in different traffic situations, three different 90 min scenarios were compared (morning peak, noon, night). Trajectory-based energy consumption and greenhouse gas emissions were compared by using the SUMO-implemented emission models HBEFA and PHEMlight, as well as data from the literature. Both diesel and electric buses showed variations in energy consumption depending on the traffic conditions, with generally lower energy consumption for electric propulsion. Temporal differences in the TTW emissions of the diesel bus were modest, with slightly higher morning values, while spatial analysis showed PM peaks in pedestrian zones, NO_x peaks during acceleration phases, and CO₂ increases after stops and in low-speed areas. The results provide spatially resolved TTW factors for integration into routing applications, excluding upstream and non-exhaust processes in line with the defined system boundary. Full article

The environmental impacts of road transport, in particular air pollution and noise, are receiving increasing attention in urban and regional planning, as they can not only predict vehicle movements but also provide detailed information on traffic volumes and speed distributions, which are indispensable for effective regulation, targeted interventions and health-conscious urban planning. This study presents an emission calculation module that can be integrated into traffic models and provides detailed estimates of pollutants emitted by road vehicles. The developed module builds on the COPERT methodology, which accounts not only for exhaust emissions such as ${\mathrm{CO}}_2$, ${\mathrm{NO}}_x$ and PM, but also for non-exhaust emissions from brake wear, tyre wear, road abrasion and evaporation. The presented system has an open architecture, enabling further customisation, particularly when local measured data are available. This contributes to building a stronger, data-driven link between transport planning and environmental protection. Full article

Brake wear particles (BWPs) represent a major source of non-exhaust particulate matter from road traffic, contributing substantially to human exposure, particularly in urban environments. While traditionally associated with coarse and fine fractions, mounting evidence shows that brake systems emit large quantities of ultrafine particles (UFPs; <100 nm), which dominate number concentrations despite contributing little to mass. This paper synthesizes current knowledge on BWP formation mechanisms, physicochemical characteristics, environmental behavior, and toxicological effects, with a specific emphasis on UFPs. Mechanical friction and high-temperature degradation of pad and disc materials generate nanoscale primary particles that rapidly agglomerate yet retain ultrafine structural features. Reported real-world and laboratory number concentrations commonly range from 10³ to over 10⁶ particles/cm³, with diameters between 10 and 100 nm, rising sharply during intensive braking. Toxicological studies consistently demonstrate that UFP-rich and metal-laden BWPs, particularly those containing Fe, Cu, Mn, Cd, and Sb compounds, induce oxidative stress, inflammation, mitochondrial dysfunction, genotoxicity, and epithelial barrier disruption in human lung and immune cells. Ecotoxicological studies further reveal adverse impacts across aquatic organisms, plants, soil invertebrates, and mammals, with evidence of environmental persistence and food-chain transfer. Despite these findings, current regulatory frameworks address only the mass of particulate matter from brakes and omit UFP number-based limits, leaving a major gap in emission control. Full article

Brake particulate matter (PM) represents a significant portion of the non-exhaust related soot emissions from all forms of transport, posing significant environmental and health concerns. Euro 7 standards only regulate road automotive emissions, while no regulation covers train transportation. This study compares two brake PM samples from rail and automotive applications. Rail brake PM was generated from composite brake pads subjected to real-world urban rapid transit braking conditions, while automotive brake PM was generated using ECE brake pads and discs under World Harmonized Light-Duty Test Cycle (WLTC) conditions. Transmission electron microscopy (TEM) and energy-dispersive X-ray (EDX) analyses were performed to assess PM morphology and composition. Both samples showed PM in coarse (10–2.5 µm), fine (2.5–0.1 µm), and ultrafine (<0.1 µm) size ranges, with angular flakes in automotive PM and rounded particles in rail PM. The rail PM exhibited a uniform size distribution, with a mean Feret diameter of 1 µm. In contrast, the automotive PM shifted toward larger particles, with ultrafine PM representing only 4% of the population. Excluding carbon and oxygen, automotive PM was dominated by iron (6 at.%) and magnesium (1 at.%). Rail PM showed lower iron (0.6 at.%) and higher aluminium (0.7 at.%) and calcium (0.8 at.%), with a broader non-C/O composition. This study tackles source-specific PM features, thereby supporting safer and more efficient non-exhaust emissions regulations. Full article