Aqueous OH Radical Production by Brake Wear Particles

SUKRITI KAPUR, Ting Fang, Kasey Edwards, Véronique Perraud, Lisa Wingen, Adam Thomas, James Smith, Manabu Shiraiwa, University of California, Irvine

     Abstract Number: 44
     Working Group: Health-Related Aerosols

Abstract
Non-tailpipe emissions, associated with brake and tire wear, are increasingly becoming important as we transition from internal combustion vehicles. Compared to tailpipe emissions that are well regulated, non-tailpipe emissions are less explored and are projected to be responsible for a major fraction of traffic-related PM. We generated brake wear particles (BWPs) with ceramic and semi-metallic brake pads using an in-house dynamometer. Particles were collected on Teflon filters and extracted in water prior to analysis. We measured Environmentally Persistent Free Radicals (EPFRs), which are long-lived radicals in the particle phase, and the production of Reactive Oxygen Species (ROS), including hydroxide (•OH), superoxide (O2•−), and hydrogen peroxide (H2O2), which play an important role in inducing oxidative stress. To understand cellular responses to BWPs, we quantified the superoxide release from macrophages upon exposure to BWPs using Diogenes chemiluminescence assay. We also determined the oxidative potential of the BWPs using the dithiothreitol (DTT) assay. Measurements showed that •OH was a dominant radical formed in water extracts, with a higher concentration measured in the semi-metallic BWPs compared to the ceramic BWPs. Ultrafine particles showed higher •OH per mass than the fine and coarse particles. However, EPFRs were not detected in any BWPs generated from the brake dynamometer system. DTT assay resulted in similar activity per mass (47 ± 16 pmol min^-1 µg^-1) for both types of brakes, indicating that both brakes have similar redox active species. These values are similar to previously reported values near highways in California (~37 pmol min^–1 μg^–1). Furthermore, metal analysis using inductively coupled plasma mass spectrometry (ICP-MS) showed iron to be the highest contributor to both brake types. These findings serve as a basis for understanding health impacts of brake wear particles.