Emissions of intermediate-volatility and semi-volatile organic compounds (I/SVOCs) from different cumulative-mileage diesel vehicles at various ambient temperatures

Abstract

The role of intermediate-volatility and semi-volatile organic compounds (I/SVOCs) in heavy-duty diesel vehicle (HDDV) exhaust remains a significant research gap in 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). The 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 8 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 proportion of oxygenated I/SVOCs (O-I/SVOCs) than LMVs (65 % vs. 42 %). Unique compounds such as phenol, alkenes, and cycloalkanes were detected exclusively in HMV emissions. Temperature effects were most pronounced at 0 °C, where only HMV emissions increased significantly, while LMV emissions remained relatively stable. A strong linear correlation (R2 = 0.93) between I/SVOC EFs and modified combustion efficiency (MCE) suggested that reduced combustion efficiency is a key driver of higher I/SVOC emissions. HMVs also showed 4 times greater secondary organic aerosol formation potential (SOAFP) compared to LMVs. This increase was smaller than the 8-fold rise in EFs, likely due to the higher O-I/SVOC content in HMV emissions.