The elevated concentration of airborne particulate matter on underground metro platforms, far higher than in aboveground environments, has drawn increasing public attention. This study builds on long-term particulate matter measurements from three underground metro platforms in Stockholm, introducing a platform-specified multi-factor model that improves on the previous single-station model. By incorporating platform-specific data, this new model enhances applicability across multiple stations and analyses the effects of train frequency, train type, passenger flow, and urban background PM on PM1, PM2.5, and PM10 concentration changes. Comparative analysis shows the new model has better flexibility, accuracy, and stability. The results reveal significant interactions between variables, with platform-specific differences in how these factors influence PM concentration rates. Model estimations indicate that as new train types replace older ones, PM concentrations will vary across platforms but are expected to approach the recommended levels set by Stockholm's transport authorities.

The use of studded tires can cause significant wear of road surfaces then also affect the air quality in urban areas. The studs of today's studded tires are manufactured from hard metal containing cobalt. In this study, we investigated using alternative cobalt-free hard metal studs to reduce particulate emissions in the future. The tire-to-road interface is subjected to both impact wear and sliding abrasive wear. The alternative hard metal studs were evaluated in parallel with standard studs using two different laboratory test rigs specially designed for wear and particulate emission testing. Stone materials commonly used in the road tarmacadam were utilized as counter material. The results showed that the cobalt-free studs generated lower particle concentrations and less road wear.

Accurate measurement and modeling of mean exhaust gas temperature (EGT) in internal combustion engines (ICEs) is paramount to improve its emission and efficiency while maintaining component durability. Sheathed thermocouples provide a robust and cost-effective EGT measurement to the detriment of accuracy due to the junction's heat balance. Literature indicates that exposing and reducing the thermocouple junction diameter improves the mean measured EGT accuracy. However, such designs can affect its interaction with the pipe wall, the conventional heat sink for sheathed thermocouples. Furthermore, characteristics of the pulsating exhaust gas flow govern junction heat convection and heat conduction linked to the exposed wire length-to-diameter (l/d) ratio. Therefore, the complex interaction between thermocouple design attributes and the pulsating exhaust flow requires isolating the effects to derive the measurement accuracy benefits from exposed junction thermocouples. This study utilizes Type-K thermocouples in sheathed (6 mm) and multiwire exposed junction (51-254μm) constructions downstream of a single-pipe exhaust of a heavy-duty diesel engine. Isolated engine speed and load sweeps provided distinct pulsating exhaust flow conditions measured using a Pitot tube for mass flux and the exposed junction heating rate to indicate the true EGT. The study highlights fundamental differences in the junction-to-pipe wall thermal interaction between sheathed and exposed thermocouples, motivating the need for distinct heat sinks and error correction before comparing measurements. Moreover, the nature of the pulsating exhaust flow conditionally enhances or undermines gains in mean EGT accuracy.

Airborne wear particle emissions from dry clutches have been investigated in terms of particle mass and number concentration, size distribution, and chemical composition of a single clutch material. This paper presents a detailed continuation of the investigation. Clutch plates of two different friction materials, i.e., from different manufacturers but for the same automobile applications, are tested and compared under different running conditions. Online measurements are made of number and mass concentration as well as size distribution. Chemical composition is analysed of both collected particles and used and unused clutch disc surfaces. Particle morphology is studied using a transmission electron microscope. Results indicate that emission profiles of the two materials are different in terms of concentrations and composition, but both materials emit fine and ultrafine particles, and the emitted particles consist of elements like Al, Fe, Cu, and Ba.

Surface roughness strongly affects the surface load-carrying capacity, transmission efficiency, and bending strength of gears. However, tooth-surface roughness is traditionally measured in terms of the average roughness parameter of the tooth surface, which is satisfactory for processing quality control but inadequate for performance analysis purposes. Each point of the tooth-profile meshes sequentially and its parameters (such as slip–roll ratio, load, and friction) temporally vary throughout the gear transmission process. Considering these variations, this paper proposes a local roughness and evaluation method for analyzing tooth-profile wear. First, the gear-tooth profile (roughness, waviness, and shape deviation) is obtained on multiple geometric scales using a roughness profilometer. Second, the acquired curves are mapped to the gear coordinate system using the orthogonal distance fitting algorithm. Thereafter, the contact of the tooth surface is analyzed under the working conditions of a gear pair. The Hertzian contact width of the working points of the tooth profile is calculated from the root to the top of the tooth, and the roughness parameter at each point is calculated in the contact area. The obtained roughness parameters are sequentially connected to obtain the local roughness curve. Finally, the tooth profile wear is determined from the local roughness curve during an FZG gear test. The local roughness curves provide accurate evaluations of the lubrication state of the tooth surface and the locations of pitting and micro-pitting on the tooth surface.

Non-exhaust emissions from brakes and tyres are becoming the major transport-related contributor of particulate matter (PM) pollution in cities. Furthermore, tyre microplastics are the major contributor of unintentionally released microplastics in all environmental compartments. The European Union introduced for the first time worldwide limits for brakes (PM10) and tyres (total abrasion mass) with the Euro 7 regulatory step. Thus, the interest in brake and tyre particles regarding health and environmental impacts has significantly increased in recent years. In this review, we summarise studies that assessed the impact of brake and tyre particles on human, mammalian, aquatic, and terrestrial cells and organisms. Furthermore, we summarise the studies that compared the impact of brake and tyre particles to other sources. We also critically examine the sampling methodologies of brake and tyre particles for health and environmental impact studies.

Polyamide 66 (PA66) exhibits excellent mechanical properties and high temperature resistance, rendering it a prevalent material for gear transmission. This study investigates the influence of lubrication, contact pressure, sliding speed and PV value (the product of pressure and velocity) on the tribological performance of PA66 gear materials under Hertzian contact using a pin-on-disc test rig. The results show that grease lubrication can significantly increase the tribological properties at high PV values. At a PV value of 30 MPa<middle dot>m/s, the friction coefficient under grease lubrication is 86.9% lower compared to that under dry conditions, and the wear rate is reduced by 96.1%. The friction coefficient and wear rate of PA66 decrease with increasing PV values under dry friction conditions. However, at a PV value of 4 MPa<middle dot>m/s, the wear rate of PA66 pins is highest when lubricated with grease, which is about 18 times that of dry condition. This is due to the grease reducing the surface mechanical strength of PA66. The wear mechanisms of PA66 primarily include adhesive wear and abrasive wear. At low PV values, abrasive wear dominates under lubrication conditions, whereas adhesive wear is predominant under dry conditions. Conversely, at high PV values, abrasive wear is more prevalent under dry friction conditions, and adhesive wear is more prominent under grease lubrication conditions.

Polyamide 66 (PA66) is one of the commonly used polymer gear materials. This paper focuses on the tribological properties of glass fiber reinforced PA66 composites in self-mated contact using a pin-on-disc tribometer. The effects of glass fiber content, PV (the product of the contact pressure and sliding speed), and lubrication on the tribological properties of the specimens are also investigated. The results show that the glass fiber reinforced PA66 exhibit higher coefficients of friction and specific wear rates than PA66 under dry sliding conditions. This is probably due to the peeled glass fibers during the sliding process acting as abrasive particles which have an aggressive effect on the surface. Under grease lubricated conditions, PA66 + 33% GF has the lowest coefficient of friction and specific wear rate due to its higher strength. Under dry sliding conditions, all specimens show the highest friction coefficient and specific wear rate at 30 MPa<middle dot>m/s with the change of PV value. Under grease lubricated conditions, all specimens show the highest friction coefficient and specific wear rate at 4 MPa<middle dot>m/s with the change of PV value. The addition of grease improves friction and wear of PA66 composites under most of the experimental conditions. However, the specific wear rates of PA66 and PA66 + 13% GF under grease lubrication are higher than those under dry sliding conditions at low PV values. This may be due to the fact that greases can reduce the surface mechanical strength of PA66 and PA66 + 13% GF.

In this study, we investigated the impact of iron-rich nanoparticles derived from different locations in the subway on the innate immune system in blood. Nanoparticles were generated from Third Rail, Rail, and Wheel materials and characterized using several techniques. The response in a human whole-blood model was analyzed using ELISA and capillary immunoelectrophoresis. All nanoparticles were iron oxides, but Third Rail nanoparticles also contained Silicon and were highly thrombo-inflammatory, activating Factor XI-induced coagulation and pro-inflammatory kallikrein/kinin pathways. Wheel and Rail nanoparticles were less reactive, mainly activating the kallikrein/kinin pathway, leading to milder inflammatory reactions. The strong thrombo-inflammatory properties of Third Rail nanoparticles are attributed to their high Silicon content. None of the nanoparticles significantly activated the complement system. In conclusion, we found that the elemental composition of nanoparticles is crucial in determining whether activation leads to kallikrein/kinin system activation and bradykinin release or Factor XI activation and thrombosis.