PM10 oxidative potential at a Central Mediterranean Site: Association with chemical composition and meteorological parameters

An extended study on the oxidative potential (OP) of PM10particles collected from December 2014 to October 2015 at a peninsular site of the Central Mediterranean basin has been performed. PM10particles have been selected to better account for all different aged/fresh particle types. Two acellular assays, i.e., the dithiothreitol (DTT) and ascorbic acid (AA) methods, were used to measure the OP of PM10particles chemically speciated by more than 40 species. DTT and AA assays provide close mean values of volume normalized OPVresponses, with similar variability range, i.e., mean OPDTTV= 0.24 ± 0.12 nmolDTTmin−1m−3and mean OPAAV= 0.29 ± 0.18 nmolAAmin−1m−3. Also mass normalized OPmresponses are similar for both assays, with mean value close to 0.008 nmol min−1μg−1. The measured OPDTTVand OPAAVare correlated with several inorganic species, namely ions and metals, and with organic/elemental carbon. The discrimination of the data according seasonality, i.e., Autumn-Winter (AW, October–March) and Spring-Summer (SS, April–September) days, shows a clear seasonal trend of correlation coefficients. In AW, OPDTTVis strongly correlated with nss-K+and nss-Ca2+, in addition to Ba, Cd, Ce, Cr, Cu, Fe, and Mn (traffic-related metals) and with EC, OC, and POC associated with the traffic exhaust source and/or with the combustion including biomass-burning source. Otherwise, OPDTTVof SS samples is correlated only with NH4+, Cu, EC, OC, and POC. The OPAAVof AW samples is well correlated with Ba, Ce, Cr, Cu, Fe, Mn, nss-K+, EC, OC, and POC, which are related with traffic and/or combustion emissions. Conversely, in SS, OPAAVis mainly correlated with NH4+, nss-K+, nss-Mg2+, nss-Ca2+, nss-SO42−, Cu, Mn, P, Pb, and oxalate, that are species related to secondary aerosols and resuspended soil from vehicular traffic and/or transported Saharan dust. These findings point the importance of both organic components and transition metals to PM oxidative properties, and also suggest that synergistic/antagonistic interactions and cross-correlations between the PM redox-active components are likely responsible for the seasonal variation of the AA and DTT assay response. The inter-correlation among all analysed species has been investigated to explain contrasting results and the negative correlations between OP values and some chemical species. Cell-free methods assessed the oxidative potential of particulate matter collected at a Central Mediterranean Site and the results were correlated with PM10chemical composition.