Objective: There is substantial evidence that exposure to airborne particulate matter (PM) from road traffic is associated with adverse health outcomes. Although it is often assumed to be caused by vehicle exhaust emissions such as soot, other components may also contribute to detrimental effects. The toxicity of fine PM (PM2.5; <2.5 mm mass median aerodynamic diameter) released from brake pads was compared to PM from other sources. Materials and methods: PM2.5 of different types of brake pads (low-metallic, semi-metallic, NAO and ECE-NAO hybrid), tires and road pavement, poultry as well as the combustion of diesel fuel and wood (modern and old-fashioned stove technologies) were collected as suspensions in water. These were subsequently aerosolized for inhalation exposures. Female BALB/cOlaHsd mice were exposed for 1.5, 3, or 6 hours by nose-only inhalation up to 9 mg/m 3. Results: Neither cytotoxicity nor oxidative stress was observed after exposure to any of the re-aerosolized PM2.5 samples. Though, at similar PM mass concentrations the potency to induce inflammatory responses was strongly dependent on the emission source. Exposure to most examined PM2.5 sources provoked inflammation including those derived from the poultry farm, wear emissions of the NAO and ECE-NAO hybrid brake pads as well as diesel and wood combustion, as indicated by neutrophil chemoattractant, KC and MIP-2 and lung neutrophil influx. Discussion and conclusions: Our study revealed considerable variability in the toxic potency of brake wear particles. Understanding of sources that are most harmful to health can provide valuable information for risk management strategies and could help decision-makers to develop more targeted air pollution regulation.

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Soot particle size profiles of a laminar co-flow diffusion flame were determined using time-resolved laser-induced incandescence (TiRe-LII) for various fuels. In the fuel matrix, both the level (0–20 vol %) and type (oxygenated versus non-oxygenated) of aromaticity was varied. Motivation for this study was earlier engine research, which demonstrated that the addition of certain aromatic oxygenates, among which anisole and veratrole, to diesel fuel manifested in lower engine out particle emissions. The co-flow burner research conducted in this study may conclude that the presence of oxygenated aromatics, although less detrimental than the non-oxygenated variety, toluene, still manifested in both greater soot volume fractions and particle sizes than was the case for the aliphatic base fuel, n-heptane. Hereby, the effectiveness of aromatic ring oxygenation was most pronounced for the first functional oxygen group. The addition of a second functional oxygen had little impact on the results.

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