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.