Source apportionment of PM10 oxidative potential at different urban/industrial sites in Italy

Oxidative potential (OP) assays are among the most widely used techniques to estimate the ability of PM to induce oxidative stress in living organisms (Bates et al., 2019). However, further efforts are still needed to assess the weight of the different PM emission sources on OP results. Statistical tools such as the Positive Matrix Factorization (PMF) applied to large chemical datasets can be used to obtain a reliable OP source apportionment. The main objective of this work was to compare the response of the three most used oxidative potential assays (ascorbic acid, AA; dithiothreitol, DTT; dichlorofluorescein, DCFH; Daellenbach et al., 2020) to different emissive sources, by considering various sites where they have different strength. To achieve this objective, several sampling campaigns were conducted from 2018 to 2023 at four sites: a traffic site in the metropolitan city of Rome (Lazio, central Italy), a peri-urban site at Ferrara in the eastern Po valley (Emilia-Romagna, north-east Italy), an urban/industrial site at Terni (Umbria, Central Italy) and a sub-urban site at Ceccano (Frosinone, Lazio, Central Italy). These sites are characterized by a different strength of ubiquitarians sources (vehicular traffic, biomass burning, soil resuspension, secondary contributions) and by different orographic and meteorological conditions. At each site PM10 samples were collected at a 24-h time resolution on both Teflon and quartz membranes, to obtain a complete chemical characterization of PM. The scheme of the used analytical procedure is reported in figure 1. PMF was applied both to identify and assess the main sources of particulate emissions in the sampling areas and to determine the weight of each emission source on the OPAA, OPDTT, and OPDCFH. Ubiquitous sources such as biomass burning, vehicular traffic, sea spray, soil, and secondary aerosol were identified, with similar profiles, at each site. Independently of site, both DTT and AA assays resulted to be mainly associated with biomass burning and vehicular traffic sources, but OPDTT resulted more sensitive to the biomass burning contribution and OPAA to the vehicular traffic one. The results obtained from the DCFH assay, which estimates the concentration of native ROS in PM, are more complex, probably also due to the low stability of some ROS.