Chemical tracers for assessing the contribution of tire wear particles in atmospheric aerosol: Analytical approaches, challenges and future perspectives

Non-exhaust traffic-derived particulate matter (PM) currently constitutes a significant fraction of urban environmental pollution, often surpassing exhaust emissions. Non-exhaust sources, originating primarily from tire and brake wear and road dust resuspension, account for an estimated 50–85% of total traffic-related PM 10 emissions. Tire Wear Particles (TWPs), and Tire and Road Wear Particles (TRWPs), are fine particles (≤5 mm) generated by the frictional interaction between tires and road surfaces, representing a major source of microplastics (MPs) in the environment. TRWPs pose significant environmental and health risks, related not only to their particulate nature (contributing to PM 10 and PM 2.5 ) but also to the leaching of toxic chemical additives and transformation products (TPs). Therefore, assessing the contribution of TRWPs to aerosol burden is critical and also challenging, due to their heterogeneous nature, variable chemical composition and the lack of standardized protocols for determination in the atmosphere. This paper reviews and compares the chemical tracers and analytical approaches employed for TRWP identification and quantification. The current consensus highlights that relying on a single compound (e.g., rubber, Zn, BTHs, phthalates) lacks the necessary specificity. Therefore, the integration of multiple tracers and the cross-validation using different analytical techniques (e.g., combining spectroscopy, Pyrolysis Gas Chromatography – Mass Spectrometry (Py-GC/MS), and High Performance Liquid Chromatography – High Resolution Mass Spectromerty (HPLC-HRMS) for organic markers) is crucial to overcome methodological limitations and understand the input of TRWPs in environmental matrices. Future research must prioritize the development of standardized protocols, certified reference materials, and the continued evaluation of transformation products to fully understand the contribution and impact of TRWPs on atmospheric pollution.