Seasonal, compositional, and meteorological drivers of PM_2.5 oxidative potential: Evidence from a year-long...

This study investigates the oxidative potential (OP) of PM_2.5 in Melbourne's inner-west region, using three complementary acellular assays: dithiothreitol (DTT), ascorbic acid (AA), and dichlorodihydrofluorescein (DCFH). PM_2.5 samples were collected over a one-year period from two urban sites located approximately 2 km apart. A clear hierarchy of assay responses was observed, with the highest mean volume-normalised OP values recorded by DTT (Site 1: 0.71 ± 0.40; Site 2: 0.80 ± 0.39 nmolmin^-1 m^-3), followed by AA (Site 1: 0.44 ± 0.25; Site 2: 0.60 ± 0.31 nmolmin^-1 m^-3)and DCFH (Site 1: 0.12 ± 0.05; Site 2: 0.13 ± 0.06 nmolH₂O₂equiv.m^-3). Strong correlations were identified between OP and carbonaceous species, particularly organic carbon (OC) and elemental carbon (EC), across all assays (r = 0.52-0.77). OP also showed significant associations with traffic- and crustal-related metals (r = 0.34-0.65), underscoring the role of multiple emission sources. Seasonal trends were assay-specific, with DTT peaking in winter, AA in autumn, and DCFH showing no seasonal variation. The study highlights pronounced temporal and spatial variability in PM_2.5 toxicity potential, demonstrating the importance of using multiple assays and compositional metrics to assess the health relevance of particulate pollution in urban environments.