Primary and Secondary Emissions from In-Service Compacted Hot Mix Asphalt Pavement

Abstract

Abstract Hot Mix Asphalt (HMA) pavement has been proposed as a significant urban source of volatile organic compounds (VOCs) and intermediate volatility organic compounds (IVOCs), yet its true atmospheric impact remains poorly understood. In this study, emissions were measured from industry-standard compacted HMA specimens containing Performance Grade 64–22 (PG 64–22) asphalt binder under both outdoor and controlled laboratory conditions. IVOC emissions peaked at C15/C16 with total emissions on the order of 2 × 10–6 mg min–1 kg–1 while VOC emissions were below method detection limits. Our results demonstrate that while emission rates are strongly temperature-dependent, both SOA mass yields and total VOC release rates are significantly lower than previously reported. At 60 °C, we estimate that total HMA-related SOA formation across the South Coast Air Basin (SoCAB) contributes only ∼5.2 kg day–1, which is less than 0.0099% of total Particulate Matter (PM2.5) reported in the 2022 AQMP. In contrast to prior work (e.g., Khare et al. 2020), which assumed complete asphalt binder accessibility and estimated a 0.00525% total sample mass loss (0.1% of binder mass loss), our non-UV data suggest an upper-bound lifetime loss of only ∼0.00035%. When applying a lower-bound estimate, the projected lifetime loss is ∼0.00002%, which is over 250 times lower than earlier estimates. This work emphasizes the importance of incorporating physically realistic, time-dependent emission behavior into urban VOC inventories and provides a refined understanding of HMA’s contribution to urban air pollution.