Gasoline Engine Exhaust Research Articles

Research on the Hazards and Emission Control Strategies of Small Agricultural Gasoline Engine Exhaust

With the widespread use of small gasoline engines in lawnmowers, generators, and chainsaws, their exhaust emissions have become a significant environmental pollution issue. Small gasoline engine exhaust primarily contains carbon monoxide (CO), nitrogen oxides (NOx), and hydrocarbons (HC), which negatively impact air quality and pose threats to human health. To mitigate these emissions, research on emission control strategies for small agricultural gasoline engines is increasingly important. This study aims to explore and evaluate different exhaust treatment technologies for small gasoline engines, including traditional catalytic converters, emerging particulate filters, electric catalysts, and selective catalytic reduction (SCR) technology. The study highlights the importance of these exhaust treatment technologies in reducing environmental pollution and promoting sustainable development, contributing significantly to environmental protection and the sustainable development of the ecological environment.

Scaling up a hollow fibre adsorption unit for on-board CCS applications using a real gasoline engine exhaust

Decarbonising road transport using on-board carbon capture and storage (CCS) is challenged by inherent space and energy limitations. Thus, to be technically and economically viable, robust and compact carbon capture units need to be developed. Hence, in this work, a scaled up hollow fibre adsorption unit was tested downstream of a real 90:10 gasoline-ethanol engine exhaust gas to evaluate its CO2 capture performance after 100 adsorption–desorption cycles. The scaled up hollow fibre adsorption unit consisted of 37 four-channel hollow fibre adsorption units coated with a thin carbon xerogel layer, referred to as the CX-coated hollow fibre module (HFM). It should be noted that this is the first study to report the results of a HFM tested under real conditions over 100 adsorption–desorption cycles and is one of the few studies that reports the desorption step. Furthermore, despite the presence of CO, THC, NOx, and H2O in the exhaust gas, the CX-coated HFM exhibited high CO2 capture stability and mechanical integrity. This was evidenced through the CX-coated HFM obtaining and maintaining an average total capacity of 1.2 mmol/g over 100 adsorption–desorption cycles, and showing no visible signs of deterioration or a loss of mechanical integrity.

Analysis of Gasoline Engine Exhaust Emissions Using a Hydrocarbon Crack System

The increase in the number of motorbikes as a means of transportation results in increased exhaust emissions resulting from combustion of gasoline engines and is dangerous for human health. The use of a Hydrocarbon Crack System is one solution to reduce exhaust emissions in gasoline engines. Hydrocarbon Crack System can perfect the combustion process resulting in low exhaust emissions. The aim of this research is knowing gasoline engine exhaust emissions using the Hydrocarbon Crack System. The research used experimental methods applied to gasoline engine motorbikes with a fuel injection system. Adding Hydrocarbon Crack System is a tool to break down hydrocarbon elements in fuel gas. The use of the Hydrocarbon Crack System in gasoline engines reduces the levels of HC 20 percent and CO 4 percent exhaust emissions at rpm 5500 and above and the exhaust temperature is 215 degrees celsius so that it can maximize the work of the catalyst.

Reducing particulate emissions by using advanced engine oil nanoadditives based on molybdenum disulfide and carbon nanotubes

Nanoadditives can be used to enhance lubricating properties of engine oils. Although many additives have been developed, molybdenum disulfide and carbon nanotubes have attracted significant attention. In this study, we demonstrate that hybrid nanostructures based on these unique materials (MoS2/CNTs) positively affect engine oil lubricating properties. Hybrid nanostructures were produced via wet chemical synthesis in impinging jet reactor. This method is characterized by easy scalability and possible continuous operation, which are crucial in material commercialization. The application of 0.5 wt% suspension exhibited the best results, reducing the friction coefficient at the engine operating temperature by up to 26%. Nanoadditives protected the lubricated parts, causing their wear to be considerably lower than the base oil. The effect of nanoadditives on the quality of exhaust gases was also investigated, which has not yet been researched. The application of the oil with MoS2/CNT reduced the emissions of solid particles in the gasoline engine exhaust gas. The total volume of particles in the exhaust gas was reduced by 91% and 49% under idling and load-running conditions. This research showed that MoS2/CNTs can be successfully used as nanoadditives in engine oils for improving tribological properties, enhancing anti-wear performance, and reducing particle emissions in exhaust gas.

Analysis of Unregulated VOCs Downstream a Three-Way Catalyst in a Simulated Gasoline Engine Exhaust under Non-Optimum Conditions

Urban air pollution is partly due to exhaust emissions from road transport. Vehicle emissions have been regulated for more than 30 years in many countries around the world. Each motor type is equipped with a specific emission control system. In gasoline vehicles, a three-way catalytic converter (TWC) is implemented to remove at the same time hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). However, TWCs are only efficient above 200 °C and at a stoichiometric air-to-fuel ratio in the exhaust. However, deviations from stoichiometry occur during fast accelerations and decelerations. This study reports the analysis of unregulated VOCs commercial mini-TWC fed by model gasoline gas mixtures. A synthetic gas bench was used to control the model exhaust containing two model hydrocarbons (propene and propane) to identify the conditions at which VOCs are created under non-optimal conditions. Most of the pollutants such as N2O and VOCs were emitted between 220 and 500 °C with a peak at around 280 °C, temperature which corresponds to the tipping point of the TWC activity. The combination of different mass spectrometric analysis (online and offline) allowed to identify many different VOCs: carbonated (acetone, acetaldehyde, acroleine), nitrile (acetonitrile, propanenitrile, acrylonitrile, cyanopropene) and aromatic (benzene, toluene) compounds. Growth mechanisms from propene and to a lesser extend propane are responsible for the formation of these higher aromatic compounds that could lead to the formation of secondary organic aerosol in a near-field area.

The Ability of Selected Plants to Absorbing CO₂, CO and HC from Gasoline Engine Exhaust

Global warming is the unusually rapid increase in the earth’s average surface temperature, which has an impact on climate change. The cause of global warming is the inhibition of heat transfer from the earth’s surface to space, which is analogous to the greenhouse effect. The occurrence of the greenhouse effect is due to the large amount of carbon dioxide (CO2) produced by the complete combustion of fuel in vehicles and industrial processes. The rising use of fossil fuels and the ongoing reduction in forest plants’ ability to absorb CO2 is to blame for the rise in CO2 levels in the atmosphere. To reduce the increase in CO2 gas, one effort that can be made is to increase CO2-absorbing plants. In this regard, plants are able to absorb CO2 and convert it into oxygen and glucose by utilizing solar heat. The purpose of this study is to determine the ability to absorb CO2 from several types of plants. The test was carried out using two closed test rooms with dimensions of 100×50×50 cm, where room 1 (first) was used to store 0.5% of CO2 emissions, while room 2 (second) was used for the plants being tested. Gas is flowed into room 2 using a fan for 300 minutes, and data collection is carried out every 60 minutes. Based on results obtained in this line of research, the best plant ability to absorb CO2 can be ordered as follows 0.25 mg/m2.hour for squirrel tail, 0.243 mg/m2.hour for trembesi, 0.2 mg/m2.hour for mahogany, 0.177 mg/m2.hour for kaffir lime, 0.166 mg/m2.hour for mango, and 0.166 mg/m2.hour for cape.

Comparison of Gasoline Engine Exhaust Emissions of a Passenger Car through the WLTC and RDE Type Approval Tests

The article presents a comparison of exhaust emission test results from a passenger car with a spark-ignition engine examined with the WLTC (Worldwide Harmonized Light-Duty Vehicles Test Cycle) test, which was carried out on a chassis dynamometer, and examined with a RDE (Real Driving Emissions) test, which was conducted in real vehicle operating conditions. The exhaust emissions and the emitted particle number in the individual phases of both tests were determined. Large disparities were found in the results of the two tests. The cold start-up had a particularly significant impact on the test results in the case of the WLTC test. This impact is much greater than in the RDE test, mainly due to the fact that the RDE test is much longer than the WLTC test. Moreover, the engine load in the RDE test was greater than in the WLTC test. As a result of the conducted analyses, it was postulated that the research should be continued in stochastic conditions for the vehicle speed function, e.g., in the implementation of the speed function determined for the real conditions of the vehicle operation.

Effect of framework Al pairing on NO storage properties of Pd-CHA passive NOx adsorbers

Three Pd/H-CHA samples were prepared containing 53.0 %, 10.8 % and 6.5 % paired Al sites at near fixed Si/Al ratio and similar Pd loading. According to H2 temperature-programmed reduction, Pd was present almost exclusively as isolated cations in the two samples containing the higher concentrations of paired Al sites, whereas in the other sample PdO was also present. Simulated lean cold start tests on the fresh samples conducted in a microflow reactor showed that the sample containing PdO stored the lowest amount of NOx. When tested with CO/H2, the sample containing 53.0 % paired Al sites showed significantly better storage capacity than the other samples and deactivated less rapidly upon sequential tests. Experiments using lean gasoline engine exhaust revealed similar trends. This study showed that a high concentration of paired Al sites in Pd/H-CHA is beneficial for NOx storage capacity, thermal durability, and minimizing deactivation in the presence of CO/H2.

A detailed review of the analysis of the different types of materials such as aluminum alloys and cast-iron piston by comparing the results we can say among these which one of the pistons had better results

A piston is a component of reciprocating engines, pumps and gas compressors. It is located in a cylinder and is made gas-tight by piston rings. In an engine, its purpose is to transfer force from expanding gas in the cylinder to the crankshaft via a piston rod and/or connecting rod. The alloy from which a piston is made not only determines its strength and wears characteristics, but also its thermal expansion characteristics. Hotter engines require more stable alloys to maintain close tolerances without scuffing. The normal temperature of gasoline engine exhaust is approximately 650ºC (923ºK). This is also approximately the melting point of most aluminum alloys and it is only the constant influx of ambient air that prevents the piston from deforming and failing. For this purpose testing different types of materials such as aluminum alloys and cast iron piston. In this project we design the three models of pistons flat head, concave head & convex heads by using Pro-Engineer 5.0 software, and imported them to make analysis in ANSYS 11.0 soft ware. And find out the vonmisses stresses, total deformation, heat distribution, and heat flux. By comparing the results we can say among these which one of the piston had better results.

The effects of variable excess air ratio and ignition timing on the performance and exhaust emissions in a direct injection Hydrogen-CNG fueled engine

This study investigates a direct injection (DI) engine fueled with compressed natural gas (CNG) enrichment with hydrogen blend (HCNG) in counter from the conversion of the port injection gasoline engine. The intention of the investigation was to examine the performance and exhaust gases from the effect of excess air ratio and timing angle changes in consequence of hydrogen increment to natural gas in comparison to gasoline engine performance and exhaust gases as a single fuel. The compression ratio was set at 14:1 with varying load at 3000 rpm, and the ignition timing was applied at −17, −19, −21, and −34°bTDC at WOT, and the amount of hydrogen enrichment to natural gas was applied at 10%, 20%, 30%, and 40%. The conditions on torque, power, heat release rate, brake specific fuel consumption, CO, and NOx were studied. Results showed that the power and torque increased by 8% with increasing the hydrogen content to 40% in fuel composition and advancing ignition timing and heat release rate as well as decreasing λ from 1.4 to 1.2 relative to the stoichiometric state. Also, the specific fuel consumption decreased by 18.5% in the optimal condition.

Experimental investigation on sucrose/alumina catalyst coated converter in gasoline engine exhaust gas.

In this study, a modified catalytic converter was employed to treat the harmful exhaust gas pollutants of a twin-cylinder, four-stroke spark-ignition engine. This research mainly focuses on the emission reduction of unburnt hydrocarbons, carbon monoxide, and nitrogen oxides at low light-off temperatures. A sucrolite catalyst (sucrolite) was coated over the metallic substrate present inside the catalytic converter, and exhaust gas was allowed to pass through it. A scanning electron microscope, X-ray diffraction, and Fourier transform infrared spectroscopy were used to investigate the changes in morphology, chemical compounds, and functional group elements caused by the reactions. Catalytic reactions were studied by varying the engine loads and bed temperatures, and the results were compared with those of the commercial catalytic converter. The results show that sucrose present in the catalyst was suitable at low temperatures while alumina was suitable for a wide range of temperatures. In the case of the modified catalytic converter, the maximum catalytic conversion efficiencies achieved for oxidizing CO and HC were 70.73% and 85.14%, respectively, and for reduction reaction at NOx was 60.22% which is around 42% higher than in commercial catalytic converter. As a result, this study claims that sucrolite catalyst is effective for low-temperature exhaust gas.

Health Risk Factors of Emissions from Internal Combustion Engine Vehicles: An Up-to-Date Status of the Problem

Introduction: Motor transport with internal combustion engines powered by diesel fuel and gasoline is one of the main sources of ambient air pollution since its emissions pose an urgent medical and environmental challenge. The objective of the study was to identify priority pollutants from emissions of motor vehicles powered by internal combustion engines based on the results of a systematic review in order to substantiate the main preventive strategy to mitigate the associated public health adverse effects. Methods: We did keyword search for relevant publications in several electronic databases, such as the Russian Science Citation Index, CyberLeninka, Scopus, and WoS. Research papers published in 2000–2021 were selected for the analysis. Out of 103 topical full-text publications, 59 works met the criteria for inclusion in the systematic review. Results: We observed that atmospheric emissions of internal combustion engines represent a complex agglomeration of gases, vapors, and particulate matter. The chemicals present in the emissions impair the oxygen transport function by inhibiting cellular respiration, cause irritation of mucous membranes, have mutagenic and carcinogenic effects, contribute to the occurrence of acid rains and to global warming. The biological effect of airborne particles largely depends on their size. It has been established that an increase in the number of airborne particles with an aerodynamic diameter less than 10 μm is associated with the risk of endothelial inflammation, thrombosis, increased cell permeability, and DNA methylation. It has been also demonstrated that a 5 µg/m3 increment in ambient concentrations of fine particles (< 2.5 μm) causes a 7 % increase in the mortality rate. At the same time, PM2.5 exposure-related risks of excess deaths from cardiovascular diseases are twice as high as those posed by exposure to PM10. Conclusions: Diesel and gasoline engine exhausts are a significant risk factor for human health. An effective preventive strategy should be aimed at replacing heavy hydrocarbon motor fuels by compressed gas using hydrogen cells and electric motors.

Thermal stability and SO2 resistance of Pd/Rh-perovskite based three-way catalyst wash-coated on cordierite monoliths

The effect of hydrothermal aging and SO2 poisoning on the three-way catalytic performance of dispersed Pd/Rh-based and Pd/Rh perovskite-based catalysts were studied by using a dynamic activity test system that simulates redox fluctuations of gasoline engine exhaust conditions. Both catalysts were supported on ceria-zirconia-alumina and wash-coated on cordierite monoliths and were characterized by ICP-OES, BET, XRD, TEM-EDX, DRIFTS, and CO chemisorption. Their performance was very close when the catalysts were fresh but, after 3 h of hydrothermal aging at 1000 °C, the dispersed Pd/Rh-based catalyst lost its performance especially with respect to C3H8 and NO conversions; however, the Pd/Rh perovskite-based catalyst kept its activity. Parallel to that, CO uptake capacity losses after hydrothermal aging were 85% and 30% for the dispersed metallic catalyst and the perovskite-based catalyst, respectively. Moreover, 20 ppm SO2 exposure decreased CO uptake capacities by 61% and 48% for the two catalysts, respectively.

Application of CFD and ANN in Predicting the Flow Nature of Flue Gas in the Catalytic Converter

The main objective of this research is to improve the performance of the catalytic converter by achieving uniform flow distribution of petrol engine exhaust gas using a distributor plate in the upstream section. The flow analysis in the catalytic converter is conducted using computational fluid dynamics (CFD) Solid works 2017 simulation software. Totally, flow simulation is carried out for twelve different cases. It has been observed that a 140 mm diffuser and distributor plate positioned 117 mm from the entrance delivers the optimal flow trajectory. This catalytic converter highly exhibits a non-linear correlation between the input and output variables. Results of such simulation study are then considered as an input for artificial neural network (ANN) model, an artificial intelligence (AI) technique. Results predicted by the ANN model are compared with CFD output. Compared outputs are in good agreement with each other. To sum up, we conclude that by introducing the distributor plate in the flow regime of the conventional catalytic converter, we can accelerate the rate of uniform flow distribution.

Transcriptional analysis of gasoline engine exhaust particulate matter 2.5-exposed human umbilical vein endothelial cells reveals the different gene expression patterns related to the cardiovascular diseases

Particulate matter (PM) causes several diseases, including cardiovascular diseases (CVDs). Previous studies compared the gene expression patterns in airway epithelial cells and keratinocytes exposed to PM. However, analysis of differentially expressed gene (DEGs) in endothelial cells exposed to PM2.5 (diameter less than 2.5 μm) from fossil fuel combustion has been limited. Here, we exposed human umbilical vein endothelial cells (HUVECs) to PM2.5 from combustion of gasoline, performed RNA-seq analysis, and identified DEGs. Exposure to the IC50 concentrations of gasoline engine exhaust PM2.5 (GPM) for 24 h yielded 1081 (up-regulation: 446, down-regulation: 635) DEGs. The most highly up-regulated gene is NGFR followed by ADM2 and NUPR1. The most highly down-regulated gene is TNFSF10 followed by GDF3 and EDN1. Gene Ontology enrichment analysis revealed that GPM regulated genes involved in cardiovascular system development, tube development and circulatory system development. Kyoto Encyclopedia of Genes and Genomes and Reactome pathway analyses showed that genes related to cytokine–cytokine receptor interactions and cytokine signaling in the immune system were significantly affected by GPM. We confirmed the RNA-seq data of some highly altered genes by qRT-PCR and showed the induction of NGFR, ADM2 and IL-11 at a protein level, indicating that the observed gene expression patterns were reliable. Given the adverse effects of PM2.5 on CVDs, our findings provide new insight into the importance of several DEGs and pathways in GPM-induced CVDs.

Formation pathways and sources of size-segregated nitrate aerosols in a megacity identified by dual isotopes

Nitrate becomes a vital secondary component in atmospheric aerosols, especially in the urban areas with effective control of sulfur emissions. The elucidation of NO3− formation pathways and sources would be very helpful for accurately modeling and controlling the particle pollution. In this study, the dual isotopic compositions (δ15N and δ18O) of size-segregated NO3− aerosols were measured at an urban site of Shanghai in the winter of 2018 and the late summer of 2019. The formation mechanisms and sources of NO3− in five size-modes and different seasons were explored by combining analyses of dual isotopes, ion concentrations, air mass back trajectories and the Bayesian isotopic mixing model. Our results showed that the δ18O-NO3− values in summer (62.1 ± 12.8‰) were generally lower than those in winter (80.1 ± 9.9‰) with the lowest values in Aitken (sub–0.1 μm) and condensation modes (0.1–0.56 μm, 48.6 ± 9.8‰). This suggested that NO2 + ∙OH pathway probably played a significant role in the NO3− formation in summer (56.1 ± 4.8%) especially in Aitken and condensation modes, while N2O5 heterogeneous and NO3 + RH/RSC (hydrocarbons/reduced sulfur compounds) pathways could be critical in winter (55.0 ± 12.6% and 28.3 ± 15.2%, respectively). The isotopic fractionation may play a critical role in the size distribution of δ15N-NO3−. Based on the formation pathways of NO3− and calculated fractionation factors εN, the contribution of major NOx sources to NO3− aerosols in Shanghai was estimated. It was found that diesel engine exhaust contributed to the highest percentages (39.3% and 32.1%) of NO3− aerosols followed by gasoline engine exhaust (30.9%) and coal combustion (29.4%) in summer and winter, respectively. The contribution of coal combustion was almost doubled in winter compared to summer whereas soil emission decreased. Our results suggest that the impact of diesel engine exhaust on particle pollution in eastern Chinese megacities should be emphasized.

Brownian coagulation of particles in the gasoline engine exhaust system: Experimental measurement and Monte Carlo simulation

In this article, Brownian coagulation of particles in the exhaust system of a gasoline engine were investigated by measuring particle size distribution (PSD) at different sampling points and Monte Carlo simulation. The measurement results show that the particle size distributions of nucleation mode (NM) change remarkably after the exhaust gas passes through the exhaust plenum chamber. The constructed coagulation model based on the classic coagulation theory can well catch the measured PSDs, particle number (PN) concentrations, and count median diameters (CMDs) along the exhaust system under both the in-cylinder direct injection and port fuel injection modes, indicating that the particle process in the exhaust system is dominated by coagulation. The NM PN concentration decreases, and the NM CMD increases in the downstream exhaust gas, and the changes are more significant at higher accumulation mode (AM) PN concentration conditions. The coagulation history provided by modelling shows that coagulation mainly occurs between two NM particles (NM-NM) or one NM and one AM particles (NM-AM). At higher AM PN concentration conditions, the NM-AM coagulation dominates and quickly eliminates NM particles, resulting in more significant NM particle reduction. The PN concentration variation as a function of time indicates that PN concentration decreases quickly at first and then the decreasing rate slows down.

Catalytic performance of hydrotalcite-like-compound-derived Ni-metal alloy catalyst for toluene reforming with gasoline engine exhaust model gas as reforming agent

Reforming of toluene with model exhaust gas was carried out as Reformed EGR of gasoline engine mainly at 773 K with Ni-M/Mg/Al (Ni 12 wt%, M = Fe, Co, Cu) prepared from corresponding hydrotalcite-like compounds. Ni-Fe/Mg/Al (Fe/Ni = 0.1–0.5) showed clearly higher performance than Ni/Mg/Al in terms of activity, coke-deposition resistance and stability. In contrast, Ni-M/Mg/Al (M/Ni = 0.25, M = Co, Cu) showed similar behaviors to Ni/Mg/Al. The optimum Fe/Ni ratio was 0.25 from toluene conversion and the suppression of benzene formation. Ni-Fe/Mg/Al (Fe/Ni = 0.25) showed high coke-deposition resistance at any position of the catalyst bed, indicating that both substrate decomposition and CO disproportionation were suppressed. The coke amount was not increased even at low temperature (773 K) or higher toluene partial pressure (toluene/H2O/N2/CO2 = 0.5–1.2/11.8/71.2/11.8, molar ratio), but the activity gradually decreased under such conditions. The Ni-Fe alloy nanoparticles in the reduced Ni-Fe/Mg/Al were almost unchanged during the reaction. The deactivated catalyst was regenerated successfully by the treatment under N2 at 873 K, catalytic use at 973 K or re-reduction. These results suggest that the deactivation was caused by carbonaceous species which can be removed easily even by N2 treatment, rather than by graphite-like coke that is difficult to be eliminated via such simple treatment.

Modelling the performance and emissions of ethanol–gasoline blend on a gasoline engine using ANFIS

ABSTRACT This research investigates the importance of the adaptive neuro-fuzzy inference method (ANFIS) to model the gasoline engine's performance and exhaust emissions using various fuels. To collect data for the creation of the planned ANFIS model, an experiment was performed on a SI engine using gasoline-ethanol blends at varying engine loads. The ANFIS model was designed to provide an association between all parameters using specific gasoline-ethanol blends and different engine loads. Then, using experimental data, engine performance parameters, and emissions were forecasted by the ANFIS model. The model findings were then contrasted with experimental values to determine the accuracy of the ANFIS predictions. The maximum correlation coefficient (R) of 0.9900–0.9999 and 95.3594% accuracy for both performance and exhaust emissions values were generated by the ANFIS model. The Mean relative errors (MRE) ranged from 0.055 to 8.396% whereas the root mean square errors (RMSE) values were small. The findings confirmed that the ANFIS is competent enough to forecast the performance and emissions of gasoline engines very efficiently.

Source apportionment of magnetite particles in roadside airborne particulate matter

Exposure to airborne particulate matter (PM) is associated with pulmonary, cardiovascular and neurological problems. Magnetite, a mixed Fe2+/Fe3+ oxide, is ubiquitous and abundant in PM in urban environments, and might play a specific role in both neurodegeneration and cardiovascular disease. We collected samples of vehicle exhaust emissions, and of heavily-trafficked roadside and urban background dusts from Lancaster and Birmingham, U.K. Then, we measured their saturation magnetic remanence and used magnetic component analysis to separate the magnetite signal from other contributing magnetic components. Lastly, we estimated the contributions made by specific traffic-related sources of magnetite to the total airborne magnetite in the roadside environment. The concentration of magnetite in exhaust emissions is much lower (3–14 x lower) than that in heavily- trafficked roadside PM. The magnetite concentration in petrol-engine exhaust emissions is between ~0.06 and 0.12 wt%; in diesel-engine exhaust emissions ~0.08–0.18 wt%; in background dust ~0.05–0.20 wt% and in roadside dust ~0.18–0.95 wt%. Here, we show that vehicle brake wear is responsible for between ~68 and 85% of the total airborne magnetite at the two U.K. roadside sites. In comparison, diesel-engine exhaust emissions account for ~7% - 12%, petrol-engine exhaust emissions for ~2% - 4%, and background dust for 6% - 10%. Thus, vehicle brake wear is by far the most dominant source of airborne magnetite in the roadside environment at the two sites examined. Given the potential risk posed, post-inhalation, by ultrafine magnetite and co-associated transition metal-rich particles to human cardiovascular and neurological health, the high magnetite content of vehicle brake wear might need to be reduced in order to mitigate such risk, especially for vulnerable population groups.