Emissions of Intermediate- and Semi-Volatile Organic Compounds (I/SVOCs) from Different Cumulative Mileage Diesel Vehicles under Various Ambient Temperatures

Abstract. The role of intermediate- and semi-volatile organic compounds (I/SVOCs) in heavy-duty diesel vehicle (HDDV) exhaust remains a significant research gap across previous studies, with limited focus on cumulative mileage and ambient temperature effects. This study analyzed gaseous and particulate I/SVOCs from four in-use HDDVs using thermal desorption two-dimensional gas chromatography-mass spectrometry (TD-GC×GC-MS). Total I/SVOC emission factors (EFs) ranged from 9 to 406 mg·km^-1, with 79–99 % in the gaseous phase. High-mileage vehicles (HMVs) emitted I/SVOCs at levels eight times greater than low-mileage vehicles (LMVs), highlighting the influence of cumulative mileage. Emission deterioration occurred under both cold-start and hot-running conditions, though HMVs showed no extra sensitivity to cold starts. HMVs also exhibited increasing emissions with component volatility, alongside a higher share of oxygenated I/SVOCs (O-I/SVOC) than LMVs (65 % vs. 42 %). Compounds such as phenol, alkenes, and cycloalkanes appeared only in HMV emissions. Temperature effects were notable at 0 °C, only HMV emissions rose significantly, while LMV emissions remained stable. A strong linear correlation (R² = 0.93) between I/SVOC EFs and modified combustion efficiency (MCE) suggests that reduced combustion efficiency drives higher I/SVOC emissions. HMVs also showed four times greater secondary organic aerosol formation potential (SOAFP) compared to LMVs. This increase was smaller than the eightfold rise in EFs, likely due to the higher O-I/SVOC content in HMV emissions.