ROS production of source-specific emissions from combustion, brake, tire and road wear

Comparison of ROS production of individual particle components from traffic-related sources can inform new health policies and emissions legislation. This work aims to quantify acellular ROS production and oxidative potential (OP) of such individual particle components from combustion, brake, tire, and road wear. Particle characteristics are probed to identify source-specific markers and improve the mechanistic description of how physical and chemical particle properties influence the response in acellular ROS production and OP measurements. Within the project, aerosol experiments are primarily performed under controlled generation in laboratory and real-scale simulations. Combustion particles were collected from a miniCAST soot generator, an experimental heavy-duty diesel engine fueled with renewable and fossil diesel, and from fire emissions of real-scale simulated arson compartment fires. Tire and road wear particles were collected from a road simulator, set up with summer, winter-friction, and studded winter tires on a cement concrete pavement. Brake emissions were collected from a pin-on-disc tribometer using different pin materials, relevant to the EU and USA, on a grey-cast iron disc. In addition to these experiments, screening methods for the generation of road emissions (without tire particles) from a wide range of surface materials will be investigated. Particles were collected on Teflon filters and extracted by sonication (3x15 min) in methanol. Fluorescence-based quantification of acellular ROS production was performed with the 2,7- dichlorodihydrofluorescein diacetate (DCFH2-DA) assay. In addition, we plan acellular OP measurements with the dithiothreitol (DTT) assay and a selection of the particle samples will be subject to in vitro and in vivo analysis of relevant toxicological endpoints. In all measurements we use a well-characterized carbon black nanomaterial (Printex 90, Degussa) with high specific surface area as a positive control. Preliminary results suggest that acellular ROS production per unit mass were of similar magnitude for the tested combustion and traffic-related emissions, but significantly lower than the positive control (1-70%). Future work aims to group particle emissions by similarity with respect to phys-chem characteristics, OP and ROS production. Such grouping is already an established method for extrapolating toxicity pathways for chemicals in general and has also been suggested for nanomaterials (Giusti et al., 2019). Therefore, grouping by similarity may also be a useful approach when considering source specific emissions.The work is conducted within three research projects funded by the Swedish Research Councils VR (2023-03952) and Formas (2021-02010), and the Swedish Competence Centre in Road Technology (Swedish Transport Administration).