About the Variability of Tire and Road Wear Marker Components in Air: From Emissions to Atmospheric Deposition

Particles originating from tire wear and road interactions, tire and road wear particles (TRWP), are an emerging class of nonexhaust emissions with growing environmental concern. Yet, little is known about their atmospheric abundance and variability due to emissions, transport and transformation processes. This study addressed this gap by quantifying six tire additives that serve as markers for the indirect detection of TRWP in complex environmental samples. Using a newly developed analytical workflow based on high-performance liquid chromatography-mass spectrometry (HPLC-MS), we traced three antiozonants, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), N-isopropyl-N'-phenyl-p-phenylenediamine (IPPD), and N,N'-diphenyl-p-phenylenediamine (DPPD), their oxidation products (6PPD quinone and IPPD quinone), and the vulcanization accelerator 1,3-diphenylguanidine (DPG) across a wide range of sample types. This single-method framework enabled us to observe marker variabilities, from pristine tire material to abrasion-related emissions from the testbed and road, airborne ultrafine particles (UFPs), and total atmospheric deposition. Marker composition varied strongly with source, emission conditions, and environmental exposure. During abrasion, 6PPD decreased by ∼90%, while 6PPD quinone increased along the emission pathway. In ambient UFP from six Bavarian (Germany) sites, mean 6PPD concentrations ranged from <0.01 to 0.55 ng m^-3. In the particulate fraction in total deposition from an urban, semi-industrial site, the ratio of oxygenated and parent PPD varied seasonally, revealing a higher degree of oxidation during summer. 6PPD dominated in the autumn and winter with an average of 6.6 ± 0.91 ng m^-2 day^-1, while 6PPDq was highest in spring and summer with average concentrations of 5.6 ± 5.91 ng m^-2 day^-1 and reaching an estimated annual deposition of 1.7 ± 0.5 μg m^-2 year^-1. By linking source materials to atmospheric samples, this study demonstrated the traceability of TRWP along their emission pathway for the first time and highlighted the importance of accounting for the chemical transformation of dedicated marker components in assessing their environmental fate.