Source Apportionment of PM_2.5 Oxidative Potential in metropolitan Melbourne: integrating PMF with multiple linear...

Despite growing recognition of PM_2.5 oxidative potential (OP) as a health-relevant metric, source-apportioned OP assessments remain scarce, particularly in the Southern Hemisphere. To the best of our knowledge, this study represents the first integration of previously published PMF-derived source contributions with oxidative potential measurements to quantify source-resolved PM_2.5 oxidative potential in an Australian metropolitan environment. Oxidative activity was measured using three complementary acellular assays (DTT, AA and DCFH) and linked with PMF-derived source contributions using multiple linear regression. Final MLR models demonstrated strong explanatory power (adjusted R² = 0.73-0.86), showing that source contributions to OP were governed not only by PM_2.5 mass but also by the chemical composition and emission characteristics of individual sources. Combustion-related sources dominated OP_v-DTT (52-53%), with biomass burning exerting a stronger influence than traffic emissions. OP_v-AA was driven by metal-rich sources, including diesel vehicles (20-22%) and crustal material (17-18%). OP_v-DCFH was strongly associated with secondary and aged aerosol, with secondary nitrate contributing 28-33% and secondary sulphate contributing 10% at Site 2. Seasonal analysis revealed winter dominance of biomass burning and diesel emissions, while spring-summer OP was strongly associated with the secondary nitrate and enhanced secondary aerosol formation, consistent with increased photochemical processing. These findings demonstrate that PM_2.5 OP is governed by aerosol chemical composition rather than particle mass alone, with primary combustion emissions and secondary nitrate influencing OP through distinct oxidative pathways. The results indicate that residential wood combustion and traffic emissions as important source-related influences on the oxidative burden of urban PM_2.5, while the strong association with the secondary nitrate highlights the potential importance of co-varying components of processed secondary aerosol.