Organic Composition of Aerosol Particles Generated from the Wear of Automotive Brake Pads

ADAM THOMAS, Maxwell Lee, Véronique Perraud, Lisa Wingen, Paulus Bauer, Michelia Dam, Barbara Finlayson-Pitts, James Smith, University of California, Irvine

     Abstract Number: 427
     Working Group: Aerosol Sources and Constituents of Emerging Importance and Their Impacts across Spatial Scales

Abstract
Electrification and the further adoption of alternative fuels in the coming decades will likely reduce pollution from vehicles significantly, but certainly not entirely. Emissions from non-tailpipe sources, such as from brake and tire wear, are known to contribute to particulate pollution. It is therefore critical to understand the chemical nature of these pollutants to better inform future environmental monitoring and emission control strategies. Crucial to this effort is the identification of potential marker compounds that can be tied to specific processes such as the heating of automotive brake pads. Here, we characterize the molecular composition of particles generated from brake wear. Particles studied include those created from frictional heating by using a custom built brake dynamometer, heating independent of friction (thermal degradation), and atmospheric oxidative aging by mixing freshly generated brake wear aerosol with ozone in a flow tube reactor. Bulk aerosol particles from these experiments were collected on filters and analyzed using an ultrahigh resolution Orbitrap mass spectrometer coupled to an UHPLC platform. Size-selected nanoparticles (sub-100 nm in diameter) were also collected and analyzed in real time using a Thermal Desorption Chemical Ionization Mass Spectrometer (TDCIMS). Observations from thermal degradation experiments, in which brake pads were heated to temperatures representative of normal use, suggest the presence of a rich diversity of oxygenated organic compounds. Some of these compounds were found to absorb UV light, as indicated by photodiode array detection. Nanoparticle composition as observed by TDCIMS further implicates the abundance of oxidized organics in these brake particles. These observations will allow us to assess the extent to which brake wear emissions contribute to particulate pollution within local communities disproportionally affected by traffic emissions.