Speciated Intermediate-Volatility and Semivolatile Organic Compounds (I/SVOCs) from Light-Duty Gasoline Vehicles: Impacts of Engine and Aftertreatment Technologies

Intermediate-volatility (IVOCs) and semivolatile organic compounds (SVOCs) from light-duty gasoline vehicles (LDGVs) are major precursors of secondary organic aerosol (SOA), yet their emission characteristics under evolving engine and aftertreatment technologies remain poorly understood. In this study, two-dimensional gas chromatography-mass spectrometry (GC-MS) (GC × GC-MS) resolved over 2000 organic species from LDGV exhausts, enabling refined emission profiles across vehicles with port fuel injection (PFI) and gasoline direct injection (GDI) engines. Oxygenated compounds, primarily acids and carbonyls, accounted for 40.5-58.5% of gaseous I/SVOCs. Although average I/SVOC emission factors showed no significant differences across the testing fleet, PFI vehicles emitted more reduced species, likely due to a lower combustion efficiency. In contrast, GDI engines significantly enhanced oxidized I/SVOC abundances by 45.6%, particularly within the intermediate-volatility range, and increased the overall oxidation state of the emitted organics. Furthermore, the application of gasoline particulate filters (GPFs) increased benzylic carbonyl emissions, suggesting potential oxidative effects. Under cold-start conditions, especially at low ambient temperatures, I/SVOC emissions were further elevated. Incorporating oxidized IVOCs into emission profiles refined the IVOC-to-total gaseous organics ratio to 27.8% and also corrected SOA prediction biases by up to 38.2%. These findings underscore the need to prioritize I/SVOCs in emission control strategies and improve SOA modeling accuracy.