Source apportionment of the oxidative potential of size-resolved urban particulate matter: Importance of combustion and regional transport

• PET (141 nm) shows highest oxidative potential during nighttime. • Vehicle (46 nm) shows second highest oxidative potential daytime. • Long-range transport enhances oxidative potential in secondary aerosols. This study examines the oxidative potential of fine particulate matter (PM 2.5 ) in a metropolitan area by analyzing particle number size distribution and chemical composition across diurnal patterns. The oxidative potential was quantified using the dithiothreitol assay, normalized to 9,10-phenanthrenequinone (QDTT-OP). The QDTT-OP was apportioned to four sources: waste PET and wood burning (141 nm, 33 %), vehicle emissions (46 nm, 32 %), long-range transport (>429 nm, 22 %), and in-situ condensation process (15 nm, 13 %). Waste burning, characterized by the presence of terephthalic acid and levoglucosan accounted for the highest QDTT-OP during nighttime. Vehicle emissions were aligned with rush-hour peaks, while long-range transport was associated with elevated levels of secondary inorganic aerosols during regional intrusion events. In-situ condensation process, characterized by ultrafine particles, occurred during the early morning hours. The integration of positive matrix factorization with particle sizing and tracer analysis facilitated detailed identification of QDTT-OP sources. These results highlight the importance of addressing both regional combustion-related emissions and transported aerosols in assessments of PM 2.5 oxidative potential and associated public health impacts.