Tire-Wear Particles as Potential Ice-Nucleating Agents in the Atmosphere

Tire-wear particles, generated through tire abrasion during driving, represent one of the largest global sources of microplastic pollution, with current annual emissions approaching 6 Tg. Due to their small particle sizes and low mass density, tire-wear particles can become airborne, undergo long-range transport, and potentially influence atmospheric processes. One critical but poorly understood pathway involves the heterogeneous freezing of supercooled cloud droplets, a key process in cloud glaciation and climate regulation. Here, we systematically investigate the ice-nucleating properties of laboratory-generated particles from summer, all-weather, and winter tires. Using optical microscopy as well as Fourier transform infrared (FT-IR) and Raman spectroscopy, we obtained particle-size distributions (∼100 μm mean diameter) and characterized the surface chemical compositions, confirming close similarity to the pristine tire materials. Ice-nucleation experiments performed with our custom-built IceBox instrument demonstrated that all tire particles consistently elevated the freezing temperatures of supercooled water droplets. The ice-nucleation performances of tire particles are found to be between feldspar and quartz, which are important mineral-based ice-nucleating agents in the atmosphere. Comparable results across all tire types suggest that major components such as rubber polymers or graphitic fillers are responsible for the observed activity. These findings establish tire-wear particles as effective atmospheric ice-nucleating agents, providing a baseline for future studies of environmentally aged tire particles and their potential roles in affecting the climate.