Airborne Brake Wear Debris:  Size Distributions, Composition, and a Comparison of Dynamometer and Vehicle Tests

Abstract

Particle size distributions of light-duty vehicle brake wear debris are reported with careful attention paid to avoid sampling biases. Electrical low-pressure impactor and micro-orifice uniform deposit impactor measurements yield consistent size distributions, and the net particulate matter mass from each method is in good agreement with gravimetric filter measurements. The mass mean diameter of wear debris from braking events representative of urban driving is 6 microm, and the number-weighted mean is 1-2 microm for three currently used classes of lining materials: low metallic, semimetallic, and non-asbestos organic (NAO). In contrast, the wear rates are very material dependent, both in number and mass of particles, with 3-4 times higher emissions observed from the low metallic linings as compared to the semimetallic and NAO linings. Wind tunnel and test track measurements demonstrate the appearance of micron size particles that correlate with braking events, with approximately 50% of the wear debris being airborne for the test vehicle in this study. Elemental analysis of the wear debris reveals a consistent presence of the elements Fe, Cu, and Ba in both dynamometer and test track samples.

Potential health risk for residents around a typical e-waste recycling zone via inhalation of size-fractionated particle-bound heavy metals

“…Cu is one of the most important elements in typical printed circuit boards and automobile brake lining, with approximately 16% and 1-14% of the contents [34,35]. Brake dynamometer testing [36] and measurements in an urban near-highway environment [37] demonstrated that airborne particle-bound Cu was concentrated in particles with diameters >1.0 m. It should be noted that the electrical low-pressure impactor used in these experiments was similar in size-segregated particles efficiency to the MOUDI sampler [36] used in the present study. As a result, it can be expected that both e-waste recycling activities and increasing transportation of e-waste would release Cu to the atmosphere.…”

The Policy Relevance of Wear Emissions from Road Transport, Now and in the Future—An International Workshop Report and Consensus Statement

“…This is due to the processes of formation, which for nonexhaust particles include mechanical abrasion, grinding, crushing, and corrosion, whereas exhaust particles are formed in combustion processes. Important exceptions to the typically rather coarse size of wear particles are nanometer-sized particles from tires, presumably formed due to thermally induced release (evaporation) of tire rubber components that form volatile droplets (Gustafsson et al, 2009b), and submicrometer particles from brake wear (e.g., Sanders et al, 2003). Because nonexhaust particles are large in comparison to exhaust particles, they contribute far more to the overall mass than to the number of particles (see for example Harrison et al, 2011).…”

Wear mechanism in automotive brake materials, wear debris and its potential environmental impact

“…Brake wear contribution to PM 10 (Particulate Matter smaller than 10μm in diameter) and PM 2.5 (Particulate Matter < 2.5 μm in diameter) per light-duty vehicle could be 0-80mg/km and 0-5mg/km, respectively [1]. Garg et al report that 35% of wear debris becomes airborne [2], while Sanders et al report up to 50% [3].…”