Molecular characterization of major oxidative potential active species in ambient PM2.5: Emissions from biomass burning and ship exhaust

Ambient fine particulate matter (PM_2.5) can catalyze the generation of reactive oxygen species in vivo, causing hazardous effects on human health. Molecular-level analysis of major oxidative potential (OP) active species is still limited. In this study, we used non-targeted high-resolution mass spectrometry to analyze the water-soluble organic components of ambient PM_2.5 samples in winter and summer. Chemical components and back trajectory analysis revealed significant impacts of biomass burning and ship emissions on PM_2.5 in winter and summer, respectively. Significance Analysis of the Microarray method and correlation analyses were combined to identify OP (OP^DTT and OP^OH) active species in characteristic organic compounds emitted from ship and biomass combustion emissions and to explore possible mechanisms. The results showed that the characteristic compounds emitted from ship were mainly organic amine compounds and contained more sulfur-containing components, while the characteristic compounds emitted from biomass burning were mainly oxygen-containing aromatic compounds of CHO and CHON groups. The high toxicity of summer PM_2.5 might derive from reduced organic nitrogen compounds (C₆H₁₄N₂O₃S, C₆H₁₂N₂O₃S, C₁₀H₉N₃O, C₆H₉N₅O₃S, and C₆H₁₄N₄O) emission from ship sources. These reduced organic nitrogen compounds can form complexes with metals, affecting their solubility and reactivity in aerosols. Phenolic hydroxyl compounds were the main contributors to the PM_2.5 OP from biomass burning in winter. Semiquinone radicals produced by oxidation of phenolic compounds can further promote the generation of reactive oxygen species through Fenton-like reactions. Our studies based on ambient PM_2.5 samples further deepened the understanding of the molecular level of organic compounds emitted from ships and biomass burning, and their association with OP.