Secondary Organic Aerosol Formation from Gaseous Tire Emissions: Laboratory Characterization and Real-World Implications

MINGHAO HAN, Don Collins, University of California, Riverside

     Abstract Number: 209
     Working Group: Chemicals of Emerging Concern in Indoor and Outdoor Aerosol: Sources, Vectors, Reactivity, and Impacts

Abstract
Reductions in tailpipe emissions have increased the relative significance of non-exhaust sources, particularly tire wear, as contributors to urban particulate pollution. However, secondary organic aerosol (SOA) formation potential from gaseous tire emissions remains poorly characterized. To address this, we constructed an experimental system combining a temperature-controlled tire enclosure, an oxidation flow reactor (OFR), and a scanning mobility particle sizer (SMPS) to quantify SOA production from tire emissions. We evaluated SOA formation from over 120 tires covering diverse brands, manufacturing years, and usage histories, at temperatures from 20–90°C to replicate realistic driving conditions. Emissions consistently increased dramatically with temperature, with SOA production at 90°C nearly three orders of magnitude greater than at 20°C. Significant variability among tire brands and production years highlights the influence of tire composition and manufacturing methods on emissions. In addition, we conducted long-term emission yield experiments by heating new tires continuously for extended periods of time and intermittently measuring SOA until emission rates significantly decreased. This procedure allowed us to directly quantify total SOA yield relative to tire mass loss, providing insights into long-term emission potential. To link laboratory results to real-world conditions, we gathered tire temperature data from over 1,000 vehicles and built a comprehensive inventory of more than 3,000 tires across the Los Angeles air basin, documenting detailed brand, model, and manufacturing year information. Integrating these real-world data with laboratory-derived SOA emission factors supports robust bottom-up regional SOA emission estimates. Further, Electron Paramagnetic Resonance (EPR) spectroscopy measurements quantified radical production and oxidative potential of tire-derived SOA, enhancing our understanding of potential health impacts. Our integrated approach advances understanding of the magnitude, variability, and environmental health implications of tire-emission SOA, emphasizing its significance for urban air quality management and potential regulatory frameworks.