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 annual emissions approaching 6 million tons. 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 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 in both immersion and contact modes, with immersion mode yielding stronger activity. Comparable results across all tire types suggest that the 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.