Method development and analysis of nanoparticle size fractions from tire-wear emissions†

Herein, we examine the generation of nanoparticles from tire and road interactions, with a focus on two key aspects: replicating real-world conditions in a controlled environment for particle generation and analysing the collected particles through both online and offline techniques. In order to generate realistic wear patterns, third body particles were used in a standardized laboratory tire testing facility across dynamic and static speeds and load profiles. The findings indicated that milled stone dust as a third body particle significantly disrupted the nanoparticle size range, complicating the differentiation between tire-based and third-body-based nanoparticles. However, using sand as a third body particle, the interference showed comparatively lower background noise within the nanoparticle region. Here, steady-state cycles were employed to discern the relationships between force events and nanoparticle generation, which were compared to analyses conducted over an entire dynamic drive cycle. The steady-state cycles revealed that high lateral forces (>2 kN) yielded the highest nanoparticle concentrations, surpassing background levels by over two orders of magnitude. Meanwhile, the drive cycle trials indicated that approximately 70% of the emitted nanoparticles throughout the entire drive cycle were semi-volatile emissions, likely originating from vaporization events. ICP-MS results confirmed the presence of tire-related elements in the nanoparticle region, but definitive attribution to the tire or road surface remains a challenge for the field. This study underscores the complexities inherent in generating, collecting, and assessing submicron tire wear particles, laying the groundwork for addressing uncertainties and refining non-exhaust tire emission methodologies.