LAUSR

Abstract The contributions of soluble and insoluble fractions of soot particles, as well as their ozonised products, to oxidative potential (OP), warrant investigation. In our study, soot particles generated under two air/fuel ratio (A/F) conditions were aged by ozone (O3) at an atmospherically relevant level in a chamber. The OP values of total soot particles and the methanol- and water-soluble fractions were measured by the dithiothreitol (DTT) assay (OPDTT). Results showed that both A/F and O3 aging influenced the OPDTT of different fractions. Lower A/F favoured increases in OPDTT for both total soot and its soluble fractions. The highest OPDTT increments after O3 aging were found in the methanol-soluble fraction of high-A/F soot and the insoluble fraction of low-A/F soot. Phenanthrene (PHE), one of the dominant polycyclic aromatic hydrocarbons (PAHs) in soot particles, was selected as a model PAH to investigate O3-PAH aging using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), with phenanthrenequinone (PQ) and 1,1′-biphenyl-2,2′-dicarboxaldehyde (BD) identified as two major ozonised products. Furthermore, the quantitative contributions of PQ and BD to the OPDTT increases in ozonised soot were extrapolated. In particular, for ozonised low-A/F soot, PQ alone contributed 12.5% to the OPDTT increase. This work highlights the vital contributions of PQ and other key ozonised products of PAHs adsorbed on soot surfaces to the enhanced OPDTT values and potential toxicity of aged soot, which enhances current understanding regarding the health effects of aged soot in the atmosphere.