Chemical constituents, driving factors, and source apportionment of oxidative potential of ambient fine particulate matter in a Port City in East China

A comprehensive year-round field campaign was conducted in the coastal city of Ningbo, China to examine the driving factors of oxidative potential (OP) of PM_2.5 and hence its potential health impacts. Using dithiothreitol (DTT) cell-free assay, OP of water-soluble (OP^ws) and methanol-soluble components (OP^meth) of PM_2.5-based samples were measured. Volume-normalised OP (OP_v^ws and OP_v^meth) were higher in heating seasons, and mass-normalised OP (OP_m^ws and OP_m^meth) peaked in summer. Five sources were identified to be DTT active in OP_v^ws, with road dust (RD) being dominant, while four sources contributed to OP_v^meth, with industrial emission (IE) as the largest contributor. Water extracted more toxic components from RD while toxic components in IE and vehicle emission (VE) were more soluble in methanol. We further compared OP values between PM_2.5 of similar concentrations and observed that OP_v^ws prevailed in PM_2.5 toxicity during clean days (PM_2.5 concentration < 38.5 µg m⁻³), while OP_v^meth became dominant when PM_2.5 concentration was larger than 69.1 µg m⁻³, implying the need to extract whole PM_2.5 using both solvents to develop the mitigation strategy for reducing the overall PM_2.5 toxicity. Efforts should be devoted to controlling the emissions from dominant sources of both OP indicators in specific episode.