Non-exhaust emissions from Brakes: Comparative assessment of physico-chemical properties in nanometric and micrometric particulates

Results from literature review show that specific studies on nanometric particles generated by automotive brakes are extremely limited. Therefore, this study focuses on: i) the generation and the physico-chemical properties of nanometric brakes emissions; ii) the correlation of their composition with the materials composing the origin friction pair; and iii) the assessment on eventual compositional differences between nanoparticulates and corresponding coarser particulates. Five different automotive brakes friction pairs are tested following standard procedures for emission assessment of disc brake systems. Nano-particulates are collected and weighed to determine corresponding concentration ranges of 0.0005 and 0.0026 mg m−3 at a flow rate of 400 m3 h−1. Several analytical techniques are deployed to investigate the physico-chemical characteristics of the collected particulates, including scanning electron microscopy, energy dispersive spectroscopy, mass spectroscopy gas chromatography and X-ray absorption spectroscopy. Main results of this study highlight significant differences in the physico-chemical composition of nanometric particulates compared to coarser ones. Clear increase in carbon content is identified when decreasing particle size distribution. Conversely, the amount of iron decreases in finer particulates, while its oxidation level increases. In addition, several Cr, Cu and Zn compounds are identified in investigated particulates, such as chromite, tenorite and zincite. Finally, for nanoparticulate emissions the polycyclic aromatic hydrocarbons (PAHs) concentrations vary largely ranging from 74 - 1460 μg g−1 and the oxygenated polycyclic aromatic hydrocarbons (OPAH) concentrations ranges from 8 to 110 μg g−1. Comparatively, lower PAHs and OPAHs values are measured in particulates from coarser fractions.