Automobile emission controls have been in place around the world since the 1960s and have been tightened year after year. Exhaust particles mainly composed of carbon emitted by internal combustion engines in automobiles are on the decreasing trend, however, with the increasing importance of powertrain alternatives, non-exhaust emissions containing brake wear particles are becoming more significant. In recently, a standard test method for measuring brake wear emissions for passenger cars was developed by the Particle Measuring Program (PMP) (United Nations, 2023). This aim is to reproduce in a laboratory experiment a driving cycle based on the worldwide average braking pattern, with particle mass (PM) sampling and particle number (PN) measurements according to generally accepted methodologies. Although this method is the basis for future regulations, it is important to evaluate the chemical composition and physical properties in order to assess environmental effects. In this study, brake wear particles derived from passenger car brakes were measured by reproducing urban driving based on brake dynamometer experiments (Hagino et al., 2016). A commercially available front brake system complying with the ECE-R90 standard was used for the passenger car brakes. Realistic driving patterns were used to observe the characterization of emission levels, particle size, and chemical composition according to driving style, using the Worldwide harmonized Light duty driving Test for brake emissions (WLTP-Brake Cycle) (Mathissen et al., 2018), the California Brake Driving Cycle (CBDC) (California Air Resources Board, 2021), the realistic driving schedule defined by the EU co-funded project LOWBRASYS (Los Angeles City Traffic (LACT)) (zum Hagen et al., 2019), and the realistic driving schedule defined by the Tokyo Metropolitan Government (Tokyo mode), which includes congestion and high-speed driving. Los Angeles City Traffic (LACT), a realistic driving schedule defined by the EU co-funded project LOWBRASYS, and the Tokyo Metropolitan roads realistic driving schedule including traffic jams and highway driving (Tokyo Metropolitan Cycle No.1-11) (Tokyo Metropolitan Pollution Research Institute, 1977). PM10 and PM2.5 were measured using filter collections with cyclones respectively. PN were measured with two CPCs (CPC3750, TSI) with a minimum measurable particle size of 10 nm, one as total PN including volatile particles (TPN10) and the other as solid PN without volatile particles after catalytic thermal elimination (SPN10). The results of this study will contribute to the investigation of brake emissions of real-world driving cycles in different urban area, the implications of friction brake energy in those cycles, and further brake emission research.

Dr. Hiroyuki Hagino, Senior Researcher, Japan Automobile Research Institute