Unraveling the Different Drivers of PM_2.5 Mass and Oxidative Potential at Two Sites of Southern Italy

The oxidative potential (OP) of PM_2.5 was investigated during two measurement campaigns in 2024 (winter and summer) done simultaneously at an urban background and a traffic site. The research provides unprecedented chemical detail for this region, integrating elemental analysis (ED-XRF), carbonaceous fractions (OC/EC, WSOC), major ions, organic tracers (sugars/levoglucosan), and water-soluble organic nitrogen (WSON). The OP was quantified by using two assays: dithiothreitol (OP^DTT) and ascorbic acid (OP^AA). Source apportionment revealed competing trends of sources limiting spatial and seasonal variabilities and distinct drivers for the two OP assays. Traffic emerged as the primary contributor to OP^AA at both sites, while OP^DTT was influenced by traffic, secondary organic aerosols (SOAs), biomass burning, and resuspension/construction. Sea spray, nitrate, and construction-related emissions significantly impacted OP^DTT but had a negligible effect on OP^AA. Primary biological aerosols (fungal spores) influenced the OP^AA. Seasonal variations showed dominance of traffic and biomass burning in winter (50-60% of OP), whereas sulfate and SOA became prominent during summer, for OP^DTT. OP^AA peaked in summer, while OP^DTT peaked in winter. Traffic-induced SOA exhibits a higher redox activity relative to its mass contribution, opposite to sulfate. Season-dependent mitigation strategies could be useful to effectively reduce the oxidative burden of PM_2.5.