Process-Specific Evaporative Emission of Semivolatile/Intermediate-Volatility Organic Compounds from Modern Gasoline Vehicles

Evaporative emissions from gasoline vehicles of semivolatile and intermediate-volatility organic compounds (S/IVOCs) are a significant yet underestimated source of secondary organic aerosol (SOA). Current models often neglect this contribution due to a lack of molecular-level data. Here, we employ comprehensive two-dimensional gas chromatography (GC × GC-TOFMS) to characterize S/IVOCs from all major evaporative processes: diurnal breathing loss, hot soak, running loss, and refueling. Our results reveal that S/IVOCs, particularly IVOCs, accounted for 16.8-58.3% of total emissions and dominate the SOA formation potential, with contributions exceeding 50% during hot soak and running loss. Molecular analysis reveals that IVOCs exhibit greater process-specificity than VOCs, marked by enrichments of oxygenated species in refueling, cycloalkanes in diurnal breathing and hot soak losses, and nitrogen-containing compounds (17.6%) in running loss. These distinct chemical fingerprints indicate contributions from nonfuel sources and selective volatilization mechanisms, moving beyond the concept of a simple fuel mixture. Furthermore, molecular fingerprints identified via volcano plot analysis provide unique signatures to differentiate emission processes. This study fills a critical knowledge gap by providing molecular-level fingerprints of S/IVOCs from the full evaporative process, thereby providing the essential insights needed to refine mobile source inventories and underscoring the necessity of incorporating these profiles into urban air quality management for the post-tailpipe era.