Reactivity of Brake Wear Particles: Reactive Oxygen Species Generation by Fresh Emissions and Iron Solubilization during Atmospheric Processing

JENNY P.S. WONG, Amelia K. Williams, Gloria G. Simmons, Mount Allison University

     Abstract Number: 411
     Working Group: Aerosol Processes and Properties in Changing Environments in the Anthropocene

Abstract
As vehicle electrification reduces tailpipe emissions, non-tailpipe sources such as brake wear particles (BWP) are expected to dominate traffic-derived particulate matter. Despite their growing importance, the health impacts of BWP, via reactive oxygen species (ROS) production, and the effects of atmospheric processing remain poorly understood.

This laboratory study investigates two aspects of BWP reactivity using particles generated to simulate mechanical wear from a semi-metallic brake pad: 1) the production of ROS by soluble and insoluble components of fresh BWP, and 2) the impact of aqueous atmospheric processing on iron solubility, as iron can drive Fenton(-like) reactions that generate ROS. Results indicate that both soluble and insoluble components contribute to ROS production, with the insoluble fraction dominating. This contribution is likely driven by surface-mediated reactions, as suggested by differential ROS production across size fractions of fresh BWP. Upon aqueous-phase processing, partial and fast conversion of insoluble to soluble iron was observed. Collectively, these findings demonstrate that the oxidative potential, and thus health impacts, of BWP evolve with atmospheric age, as changes in metal solubility alter the relative contributions of soluble and insoluble components involved in ROS production.