Unraveling the Different Drivers of PM2.5 Mass and Oxidative Potential at Two Sites of Southern Italy

The oxidative potential (OP) of PM2.5 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 (OPDTT) and ascorbic acid (OPAA). 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 OPAA at both sites, while OPDTT was influenced by traffic, secondary organic aerosols (SOAs), biomass burning, and resuspension/construction. Sea spray, nitrate, and construction-related emissions significantly impacted OPDTT but had a negligible effect on OPAA. Primary biological aerosols (fungal spores) influenced the OPAA. Seasonal variations showed dominance of traffic and biomass burning in winter (50–60% of OP), whereas sulfate and SOA became prominent during summer, for OPDTT. OPAA peaked in summer, while OPDTT 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