DLR Tire and Road Wear Particle Emission Testing methodology - Collection System Influence and Repeatability Assessments

Abstract

Summary This study addresses the methodological gaps in the quantification of TRWP emissions by developing a robust, reproducible testing framework. Through meticulous control of critical parameters which are influencing detected particle mass and number concentrations, the research demonstrates that even under standardized conditions, the choice of aerosol collection system significantly impacts measurement outcomes. The primary focus is not on quantifying absolute emission factors or systematically evaluating the effects of influencing parameters. A more detailed investigation into emission factors or the influence of specific factors (e.g., speed, tread temperature, surface type) on TRWP emissions would require a dedicated experimental design involving systematic variation of these parameters and focused factor analysis, which is beyond the scope of this study. In this study’s scope, a comparative analysis between housing-based and nozzle-based collection systems highlighted the critical importance of collection system design. The results showed a distinct difference between the two collection systems: the nozzle setup exhibited high variability in air speed during driving conditions, likely due to its open structure, whereas the housing system maintained more stable air speed. Furthermore, particle number and mass concentrations were consistently higher in the housing system, up to three times greater for number concentrations. These findings highlight when targeting comparison among different tire types, conditions or sizes the influence of collection system geometry effects TRWP measurement outcomes and different systems can provide different particle characterization abilities. While the housing collection system exhibited slightly higher measurement consistency for both particle size fractions, suggesting its suitability for standardized TRWP sampling, the nozzle system demonstrated comparably consistent coefficients of variation. Although the nozzle system resulted fewer particles, the similarity in CoV values indicates that while collection system geometry significantly affects particle characterization abilities, a rigorously executed measurement methodology effectively reduces variability. These insights are pivotal for achieving methodological robustness and accuracy in future particle emission evaluations and optimizing measurement practices. Statistical analyses conducted according to ISO standards allowed accurate measurement of repeatability and variability, reinforcing the robustness and reliability of the FIGURE 11 PM2.5 and PM10 deviations for 4 repeated test and comparison of the CoV for background measurements TABLE 8 Coefficient of variation values of PM2.5 and PM10 mass concentrations for the housing and nozzle collection systems and background measurements System PM2.5 CoV (%) PM10 CoV (%) Housing 5.5 6.3 Nozzle 5.8 9.0 Background 14.7 13.212 DLR TIRE AND ROAD WEAR PARTICLE EMISSION TESTING METHODOLOGY established methodology. However, the study recognizes its limitations, such as assumptions regarding realistic particle generation conditions during actual road driving scenarios, uniform particle density assumptions in OPS mass calculations, and potential underestimations of particle concentrations by the nozzle-based system. These factors underline the necessity for continuous methodological refinement, diverse test environments, and improved sampling efficiencies, particularly for both small and coarse size fractions. Although being at an early stage of development, this study significantly contributes to the standardization of TRWP emission measurement methodologies in a comparable framework, giving a measurement quality control procedure in this field and providing a foundational base necessary for effectively addressing vehicular microplastic pollution within the airborne fraction. By presenting the comparative efficiency and limitations of aerosol collecting techniques, the findings enhance scientific understanding of TRWP measurement research and support environmental policies aimed at mitigating airborne TRWP pollution.