Brake Wear Emissions of Gas-Phase Sulfuric Acid, Inorganic Nitrogen Species and Oxidized Organics

MICHELIA DAM, Adam Thomas, Véronique Perraud, Lisa Wingen, Barbara Finlayson-Pitts, James Smith, University of California, Irvine

     Abstract Number: 259
     Working Group: Aerosol Chemistry

Abstract
Non-exhaust emissions are projected to become the dominant source of traffic-related emissions as our vehicle fleet transitions from combustion engines to electric. Although there is a rapidly increasing body of work showing that braking produces significant particulate matter emissions, characterizing the overall gas emission profile from these braking processes is a key, missing component of understanding their overall effects on health and climate in urban environments. To address this fundamental knowledge gap, we measured gas emissions from two commonly used brake types (semi-metallic, ceramic) using a home-built brake dynamometer and chemical ionization mass spectrometry (nitrate-CIMS and iodide-CIMS). Both moderate and heavy braking conditions were assessed. We found that sulfuric acid, nitrous acid (HONO), other inorganic nitrogen species, and oxidized organics were produced by both brake types, with production rapidly increasing during heavy braking. Measured gases were correlated with other gas compounds emitted during braking (CO, NOx), as well as rotor and chamber temperatures to help determine dominant formation processes and sinks. Ratios of HONO to NOx were found to be higher than those measured from tailpipe emissions during heavy braking conditions. Additionally, the overall magnitude of emissions was found to decrease with increasing wear on the brakes. Our results indicate that brake emissions are a non-negligible source of these reactive gases that impact atmospheric processes including particle formation and growth that need to be considered for effective mitigation strategies in the near future.