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About the variability of tire and road wear marker components in air: from emissions to atmospheric deposition
Summary
Scientists developed a new method to track tiny particles that come from car tires wearing down on roads, which are now recognized as one of the biggest sources of microplastic pollution worldwide. They found these tire particles can travel far from roads through the air and change into different chemicals, including some that may be harmful. This matters because these airborne tire particles could pose risks to human health and the environment, but we're just starting to understand how much is actually in the air we breathe.
The question whether tire and road wear particles (TRWP) impact air quality has been widely debated since decades. Today, TRWP are recognized as one of the largest sources of microplastic pollution worldwide. When airborne, TRWP can be transported far away from roads and transformed by weathering posing a potential risk to both ecosystem integrity and human health. Yet, little is known about their atmospheric abundance and variability due to emissions, transport and transformation processes.One reason for this knowledge-gap is the lack of tools for direct identification and quantification of TRWP in atmospheric samples. Recently it has been suggested to make use of organic additives as marker components, that are specific to tire wear and traceable. Here, we developed a new analytical workflow based on high-performance liquid chromatography–mass spectrometry (HPLC-MS), to trace six selected TRWP marker components: the 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, IPPD-quinone), and the vulcanization accelerator 1,3-diphenylguanidine (DPG). We designed a single-method framework to observe marker variabilities across a wide variety of sample types: from pristine tire material, to abrasion-related emissions from testbed and road, airborne ultrafine particles (UFP), and total atmospheric deposition. Marker composition varied strongly with source, emission conditions, and environmental exposure.We highlight a large tire-to-tire variability and significant losses of the antiozonants during abrasion, which both challenge quantification and calculation of the original TRWP mass. Moreover, we show the presence of TRWP in airborne ultrafine particles and atmospheric total deposition. These samples revealed a significant degree of oxidation, which should to be taken into account when considering the traceability of such markers and their environmental impact, e.g. through formation of harmful oxidation products.This project is financed by the Bavarian State Ministry of the Environment and Consumer Protection and the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) SFB 1357 - project nr. 391977956.