Airborne Particle Emissions Research Articles

Correlations between the wear of car brake friction materials and airborne wear particle emissions

Airborne wear particles emitted from transport vehicle brakes are one of the main sources of toxic metals in inhalable particulate matter. Prediction of wear particle emissions may become more accurate if the relationship between the wear and particle emission characteristics is known. An experimental study was performed to investigate proportional correlations between the mass wear, 0.01–0.42 μm particle emission measured by a NanoScan SMPS Nanoparticle Sizer (SMPS) and 0.3–10 μm particle emission measured by an Optical Particle Sizer (OPS). Several car brake low-metallic materials in the form of pin samples were tested against steel disc samples at different values of the contact pressure and sliding velocity. The pin-on-disc friction pair was placed in a clean chamber to eliminate external particle sources. The obtained results suggest a strong proportional correlation between the disc sample wear and pin sample wear. OPS and SMPS particle concentrations were also revealed to strongly correlate between each other. By contrast, the disc sample wear exhibited weak correlations with the particle concentrations for most of the materials.

Recycling of worn out brake pads \u2012 impact on tribology and environment

Disc brake systems are widely used on commercial vehicles for braking. The brake pads are usually replaced by new ones before being totally worn out. Current methods to deal with the replaced brake pads include landfill and combustion, resulting in a huge waste of resources and increase of CO2 footprint. From a sustainable point of view, this study aims to evaluate the feasibility of recycling replaced brake pads by addressing a protocol recycling procedure. The results show that the recycled brake pads yield similar friction, wear and airborne particle emission to virgin brake pads. A streamlined life cycle assessment is conducted to compare the environmental impacts between producing virgin brake pads and recycling replaced brake pads. Energy consumption and CO2 footprint of the recycled brake pads are 36% and 34% less than virgin brake pads, indicating that recycling could be a promising method of handling replaced brake pads.

A Study of the Effect of Brake Pad Scorching on Tribology and Airborne Particle Emissions

Non-exhaust wear emissions from disc brakes affect the air quality in cities throughout the world. These emissions come from the wear of the contact surfaces of both the pads and disc. The tribological and emissions performance of disc brakes strongly depend on the contact surface characteristics of the pads and discs. The surfaces of conventional pads are scorched by heating it to several hundred degrees to make the resin carbonize down to a few millimetres deep into the pad. This is done to have a shorter run-in period for new pads. It is not known how scorching will affect the amount of airborne particle emissions. Therefore, the aim of the present study is to investigate how pad scorching influence the airborne particle emissions. This is done by comparing the pin-on-disc tribometer and inertia dyno bench emission results from a Cu-free friction material run against a grey cast iron disc. Three types of modified friction material surfaces have been tested: scorched, extra-scorched and rectified. The results show that the level of scorching strongly affects the airborne particle emissions in the initial phase of the tests. Even if the scorched layer is removed (rectified) before testing, it seems like it still has a measurable influence on the airborne particle emissions. The results from the tribometer tests are qualitatively in line with the inertia dyno bench test for about the first forty brake events; thereafter, the airborne particle emissions are higher for the scorched pads. It can be concluded that it seems that the level of scorching has an adverse influence on both the tribological performance and level of particle emissions.

Nanoparticle exposure and hazard in the ceramic industry: an overview of potential sources, toxicity and health effects

The ceramic industry is an industrial sector of great impact in the global economy that has been benefiting from advances in materials and processing technologies. Ceramic manufacturing has a strong potential for airborne particle formation and emission, namely of ultrafine particles (UFP) and nanoparticles (NP), meaning that workers of those industries are at risk of potential exposure to these particles. At present, little is known on the impact of engineered nanoparticles (ENP) on the environment and human health and no established Occupational Exposure Limits (OEL) or specific regulations to airborne nanoparticles (ANP) exposure exist raising concerns about the possible consequences of such exposure.In this paper, we provide an overview of the current knowledge on occupational exposure to NP in the ceramic industry and their impact on human health. Possible sources and exposure scenarios, a summary of the existing methods for evaluation and monitoring of ANP in the workplace environment and proposed Nano Reference Values (NRV) for different classes of NP are presented. Case studies on occupational exposure to ANP generated at different stages of the ceramic manufacturing process are described. Finally, the toxicological potential of intentional and unintentional ANP that have been identified in the ceramic industry workplace environment is discussed based on the existing evidence from in vitro and in vivo inhalation toxicity studies.

Tribology performance, airborne particle emissions and brake squeal noise of copper-free friction materials

Copper and its alloy have been widely used in the formulation of non-asbestos organic (NAO) friction materials as reinforcements and/or additives. But U.S.A has raised a legislation to reduce the copper content in friction materials due to the toxicity of copper in wear debris. Thus, there is a need to develop copper-free friction materials which also owns the desired tribology performance. In the present study, two new copper-free non-asbestos organic (NAO) friction materials were developed by replacing the copper fiber with steel fiber (named SFM) or ceramic fiber (named CFM). Friction and wear behaviors, airborne wear particle emissions and brake squeal noise of these two copper-free friction materials were evaluated and compared with a reference copper containing friction material (RFM) by using a pin-on-disc test rig. Results show that all friction materials have comparable friction coefficients, and the specific wear rates of SFM and CFM are larger than that of RFM. The mean fractal dimension of RFM surface is larger than those of SFM and CFM surfaces. For the airborne particle emissions, RFM presents the lowest particle number emissions and particle mass concentrations (PMCs) of PM10 (particles smaller than 10 μm) and SFM presents the highest values of these two results. For brake squeal noise, the brake squeal noise of all friction materials has comparable A-weighted sound pressure levels (SPLs). It can be concluded that the replacement of copper fiber with steel and ceramic fibers can obtain comparable tribology performance and brake squeal noise, but it will increase the particle emissions.

Particle emission of organic brake pad material: A review

Wear of a brake pad emits airborne particles and is a major environmental issue. This review paper deals with the analysis of different brake pad composite materials and their wear phenomenon. The volume fraction and size distribution of non-asbestos organic airborne particles emitted from the brake pad material with time, load and speed have also been discussed under different braking conditions. The airborne particles are measured by different aerosol instruments. TSI P-Trak, GRIMM aerosol spectrometer and scanning mobility particle sizer were used by different researchers for measuring ultrafine particles, micron-sized particles and aerodynamic nanoparticles, respectively. This paper shows that the wear particles emitted from the brake pad material vary in diameter between 10 nm and 10 μm under various loads and sliding velocities. These airborne particles such as coarse fine (diameters > 1 μm), fine (diameters between 100 nm and 1 μm) and ultrafine (diameters < 100 nm) particles are responsible for health hazards to the human respiratory system. This study has accumulated the data of different ingredients of the brake pad with airborne particle emission from various studies, which may be helpful for the evolution of new composite materials in the near future.

Friction, wear and airborne particle emission from Cu-free brake materials

Abstract Cu is required to be abated in brake pads due to its toxicity. There are on the market several Cu-free brake pads. These Cu-free brake pads are only evaluated regarding their friction and wear performance, whereas, their airborne particle emissions are not considered. A pin-on-disc tribometer is used to evaluate the friction, wear and airborne particle emission from two Cu-free commercial brake pads used in the Europe. Moreover, a commercial brake pad containing Cu is evaluated as a reference. The results indicate that Cu-free brake pads yield comparable coefficient of friction as the Cu-contained brake pad. All three brake materials result in similar wear to the mating brake rotor. Cu-free brake pads generate more airborne particles than Cu-contained brake pad.

An FEA approach to simulate disc brake wear and airborne particle emissions

Emissions from disc brake wear adversely affect the air quality in cities. Finite Element Analysis (FEA) approaches focussing on the macroscopic wear of pads and rotors can be found in the literatu ...

Airborne particle emission rates and doses received in operating rooms from surgical smoke

The surgical smoke is commonly generated by electrosurgery, i.e. by the heat-producing device used in operating rooms for cutting tissues and coagulating small blood vessels through the use of high-frequency electrical current. Health effects due to the exposure to surgical smoke were recently recognized, thus the scientific community is currently paying more attention to such research field. In particular, studies focusing on the improvement of the effectiveness of filtration systems and mechanical ventilation systems were carried out, nonetheless, a gap of knowledge on the particle concentration levels in the operating rooms and on the emission rate of the surgical procedures still exists.In the present paper an experimental analysis was performed (i) to estimate the particle emission per unit time for several types of surgery for different aerosol metrics and (ii) to measure the dose of both sub-micron and super-micron particles received by workers and patients. To this purpose, samplings were performed in seven operating rooms located in three different Italian hospitals.The median emission rates in terms of particle number and mass concentrations amongst the surgery procedures investigated varied in the 1.59–3.21 × 1011 part. min−1 and 0.09–0.32 mg min−1 ranges, respectively, leading to corresponding median particle concentration levels of 0.7–1.2 × 104 part. cm−3 and 5–13 μg m−3.Finally, the median particle surface area dose received by personnel working in the operating rooms during the surgery procedures varied from 5 to 12 mm2.

A comparison of airborne wear particle emission models based on metro station measurements

The main sources of non-exhaust particles around metro systems are the wear from wheel-rail contact, brake contact and the contact between mechanical parts in electric power systems. In order to predict the PM10 levels on underground metro platforms, the relation among time, train frequency and PM10 level should be investigated. Two types of particle emission models have previously been published to determine the PM10 level on underground train platform; these are the linear model and the conservation model. The aim of this study is to compare the results from the two models with a set of field measurements PM10. In 2016, a set of field measurements are performed on four underground metro platforms in Stockholm. The predicted PM10 values from the two models are compared with the measurement data. The accuracy of the two models is analysed and the behaviours of the two models in high and low train frequency regions are separately discussed. (Less)

Towards a two-part train traffic emissions factor model for airborne wear particles

In 2017 a new railway tunnel containing two stations opened in Stockholm, Sweden. A series of field measurements were carried out on the platforms in this tunnel before and after it was opened for normal traffic. These measurements were used to investigate the contribution of airborne particle emissions from wear processes to total train emissions. This field data was used to develop a two-part train traffic emission factor model for PM10. The two parts are the accumulative effect term (relating to operating distance such as wheel-rail contact and overhead electric line sliding contact) and a brake effect term (relating to the number of braking operations such as brake disc and brake pad contact). The results show that operating a single trial train at a higher than normal frequency on an otherwise empty platform increases the platform particulate concentration until the concentration reaches a steady value. The model suggests that brake emissions account for about 50% of the total emissions measured in the tunnels.

A pin-on-disc study of airborne wear particle emissions from studded tyre on concrete road contacts

Studded tyres wear surfaces of winter roads, generating inhalable airborne particles. In this study, four concrete road materials and two stud geometries were investigated in terms of wear, road material hardness and airborne particle concentration. The sliding contact between studded tyres and road materials was studied using a pin-on-disc machine in a clean chamber. The results show that the normal load and the stud size have a large influence on the wear and particle emission. It was found that the wear and particle concentration are inversely proportional to the hardness of the aggregate in the road material and proportional to the sliding distance. The particle size distribution has peaks at 0.2 µm, 1 µm and 2 µm.

Molecular composition of particulate matter emissions from dung and brushwood burning household cookstoves in Haryana, India

Abstract. Emissions of airborne particles from biomass burning are a significant source of black carbon (BC) and brown carbon (BrC) in rural areas of developing countries where biomass is the predominant energy source for cooking and heating. This study explores the molecular composition of organic aerosols from household cooking emissions with a focus on identifying fuel-specific compounds and BrC chromophores. Traditional meals were prepared by a local cook with dung and brushwood-fueled cookstoves in a village in Palwal district, Haryana, India. Cooking was done in a village kitchen while controlling for variables including stove type, fuel moisture, and meal. Fine particulate matter (PM2.5) emissions were collected on filters, and then analyzed via nanospray desorption electrospray ionization–high-resolution mass spectrometry (nano-DESI-HRMS) and high-performance liquid chromatography–photodiode array–high-resolution mass spectrometry (HPLC-PDA-HRMS) techniques. The nano-DESI-HRMS analysis provided an inventory of numerous compounds present in the particle phase. Although several compounds observed in this study have been previously characterized using gas chromatography methods a majority of the species in the nano-DESI spectra were newly observed biomass burning compounds. Both the stove (chulha or angithi) and the fuel (brushwood or dung) affected the composition of organic aerosols. The geometric mean of the PM2.5 emission factor and the observed molecular complexity increased in the following order: brushwood–chulha (7.3 ± 1.8 g kg−1 dry fuel, 93 compounds), dung–chulha (21.1 ± 4.2 g kg−1 dry fuel, 212 compounds), and dung–angithi (29.8 ± 11.5 g kg−1 dry fuel, 262 compounds). The mass-normalized absorption coefficient (MACbulk) for the organic-solvent extractable material for brushwood PM2.5 was 3.7 ± 1.5 and 1.9 ± 0.8 m2 g−1 at 360 and 405 nm, respectively, which was approximately a factor of two higher than that for dung PM2.5. The HPLC-PDA-HRMS analysis showed that, regardless of fuel type, the main chromophores were CxHyOz lignin fragments. The main chromophores accounting for the higher MACbulk values of brushwood PM2.5 were C8H10O3 (tentatively assigned to syringol), nitrophenols C8H9NO4, and C10H10O3 (tentatively assigned to methoxycinnamic acid).

Open System Tribology in the Wheel–Rail Contact—A Literature Review

The tiny contact zone (approximately 1 cm2) where steel wheel meets steel rail is fundamental to rail transport. This work is a comprehensive presentation of recent research in wheel–rail contact tribology. It stresses that, unlike gears or rolling bearings which are sealed contacts with reduced exposure to the surrounding environment, a wheel–rail contact is an open system that is exposed to dirt and particles as well as to applied and natural lubrication (the latter category includes rain, dew, and biological materials such as leaves). As an open system contact, it also radiates sound and airborne wear particles. These characteristics of an open system underscore the need for special studies of open system tribology. Areas requiring study include airborne particle emissions and the environmental effects of applied lubrication and friction modification. Given that adhesion, wear, and sound and particle emission are closely related in an open system, these should be studied together rather than independently.

Effect of humidity on the tribological behaviour and airborne particle emissions of railway brake block materials

A pin-on-disc tribometer placed in a one-way ventilated chamber was used to investigate the effect of relative humidity on the tribology and airborne particle emission of three commercial railway b ...

A pin-on-disc tribometer study of disc brake contact pairs with respect to wear and airborne particle emissions

In the EU, PM10 from the wear of disc brakes can contribute up to 50% of the total non-exhaust emissions from road transport. The wear originates from the contact surfaces of the friction material and the disc. One possible way to decrease PM10 emissions is to change the materials of the contact pair in terms of composition and coatings. The wear and particle emissions of three novel friction material formulations, one novel disc formulation, one disc WC/CoCr coating realized with the HVOF technique, and one disc surface treatment realized by a nitriding process, were investigated. Pin-on-disc tests were run to rank the novel materials in terms of specific wear rate and particle number and mass rate. The results show that it is possible to achieve a reduction in particle emissions of up to 50% by changing the materials of the contact pair.

Estimation of Cancer Risk Due to Exposure to Airborne Particle Emission of a Commercial Three-dimensional Printer.

Estimation of Cancer Risk Due to Exposure to Airborne Particle Emission of a Commercial Three-dimensional Printer.

Concentric Ring Method for generating pollen maps. Quercus as case study

Mapping pollen concentrations is of great interest to study the health impact and ecological implications or for forestry or agronomical purposes. A deep knowledge about factors affecting airborne pollen is essential for predicting and understanding its dynamics. The present work sought to predict annual Quercus pollen over the Castilla and León region (Central and Northern Spain). Also to understand the relationship between airborne pollen and landscape. Records of Quercus and Quercus pyrenaica pollen types were collected at 13 monitoring sites over a period of 8years. They were analyzed together with land use data applying the Concentric Ring Method (CRM), a technique that we developed to study the relationship between airborne particle concentrations and emission sources in the region.The maximum correlation between the Quercus pollen and forms of vegetation was determined by shrubland and “dehesa” areas. For the specific Qi pyrenaica model (Q. pyrenaica pollen and Q. pyrenaica forest distribution), the maximum influence of emission sources on airborne pollen was observed at 14km from the pollen trap location with some positive correlations up to a distance of 43km. Apart from meteorological behavior, the local features of the region can explain pollen dispersion patterns. The method that we develop here proved to be a powerful tool for multi-source pollen mapping based on land use.

Real-Time Ultrafine Aerosol Measurements from Wastewater Treatment Facilities.

Airborne particle emissions from wastewater treatment plants (WWTP) have been associated with health repercussions but particulate quantification studies are scarce. In this study, particulate matter (PM) number concentrations and size distributions in the ultrafine range (7-300 nm) were measured from two different sources: a laboratory-scale aerobic bioreactor and the activated sludge aeration basins at Orange County Sanitation District (OCSD). The relationships between wastewater parameters (total organic carbon (TOC), chemical oxygen demand (COD), and total suspended solids (TSS)), aeration flow rate and particle concentrations were also explored. A significant positive relationship was found between particle concentration and WWTP variables (COD: r(10) = 0.876, p <.001, TOC: r(10) = 0.664, p <.05, TSS: r(10) = 0.707, p <.05, aeration flow rate: r(8) = 0.988, p <.0001). A theoretical model was also developed from empirical data to compare real world WWTP aerosol number emission fluxes with laboratory data. Aerosol number fluxes at OCSD aerated basins (9.8 × 104 lbs/min·cm2) and the bioreactor (7.95 × 104 lbs/min·cm2) were calculated and showed a relatively small difference (19%). The ultrafine size distributions from both systems were consistent, with a mode of ∼48 nm. The average mass concentration (7.03 μg/cm3) from OCSD was relatively small compared to other urban sources. However, the in-tank average number concentration of airborne particles (14 480 lbs/cm3) was higher than background ambient concentrations.

Towards the ranking of airborne particle emissions from car brakes – a system approach

Airborne particulate matter emitted from motor vehicle brakes is a contributor to urban air quality. Therefore, a method to rank brake pairs (pads and rotors) with respect to their particle emission factors in a reliable way is needed to develop a low-emission disc brake. A novel inertial disc brake dynamometer designed for brake particle emission studies, a modified SAE J 2707 cycle, an electrical low-pressure cascade impactor and a filter are used to test five different pad materials against cast-iron rotors. By changing only the pad materials, it is shown that the differences between the mass emission factor and the number emission factor of the the worst brake pair and those of the best brake pair decreases by more than four times and 19 times respectively. Furthermore, the results show that the material combination ranked the best in terms of the mass emission factor is ranked the worst in terms of the number emission factor. The results reveal that this combination of a test stand, a test cycle and particle instruments can discriminate between different brake pair materials in a reliable way in the case of the mass emission factors while more research has to be carried out in the case of the number emission factors.