Laboratory Study of the Contribution of Phenolic Resin Thermal Degradation to Automotive Brake Emissions

BERENICE ROJAS, Adam Thomas, Lisa Wingen, Madeline Cooke, Véronique Perraud, Barbara Finlayson-Pitts, James Smith, University of California, Irvine

     Abstract Number: 651
     Working Group: Chemicals of Emerging Concern in Aerosol: Sources, Transformations, and Impacts

Abstract
Understanding vehicle emissions is crucial in mitigating poor air quality. The national trend towards electric vehicles has reduced tailpipe emissions but has left non-tailpipe emissions such as brake and tire wear as significant contributors to emissions. Most modern passenger vehicles use ceramic or semi-metallic brake pads, including phenolic resins as binder agents that undergo frictional heating during braking. Severe braking conditions can lead to the decomposition of these resins, increasing wear and releasing harmful ultrafine particles (UFPs) into the environment. While it is known that braking can emit UFPs, the contribution of different brake pad materials and the impact of phenolic resin decomposition on the formation and composition of these particles remain unclear. In this study, we investigate the chemical composition of UFPs from the thermal degradation of phenolic resins and compare them with emissions from a light-duty vehicle disc brake system equipped with ceramic and semi-metallic brake pads. In the thermal degradation experiments, phenolic resin samples were heated in a controlled manner to simulate thermal heating during braking, releasing volatile organic compounds, which resulted in the direct nucleation of UFPs. In the disc brake simulation experiments, a custom-built brake dynamometer was used to simulate braking over various operating conditions in real-world driving. UFPs formed from the disc brakes and phenolic resin heating experiments were collected on filters and analyzed using liquid chromatography coupled with high-resolution Orbitrap mass spectrometry. By comparing composition data obtained during these experiments, we identify key contributors to UFP formation from brake pads, guiding the development of improved brake pad materials that minimize environmental and health impacts. Our findings will highlight the importance of brake pad composition and its impact on air quality.