Source apportionment of PM_2.5 oxidative potential in an East Mediterranean site

This study aimed to evaluate the oxidative potential (OP) of PM_2.5 collected for almost a year in an urban area of the East Mediterranean. Two acellular assays, based on ascorbic acid (AA) and dithiothreitol (DTT) depletion, were used to measure the OP. The results showed that the mean volume normalized OP-AA_v value was 0.64 ± 0.29 nmol·min^-1·m^-3 and the mean OP-DTT_v was 0.49 ± 0.26 nmol·min^-1·m^-3. Several approaches were adopted in this work to study the relationship between the species in PM_2.5 (carbonaceous matter, water-soluble ions, major and trace elements, and organic compounds) or their sources and OP values. Spearman correlations revealed strong correlations of OP-AA_v with carbonaceous subfractions as well as organic compounds while OP-DTT_v seemed to be more correlated with elements emitted from different anthropogenic activities. Furthermore, a multiple linear regression method was used to estimate the contribution of PM_2.5 sources, determined by a source-receptor model (Positive Matrix Factorization), to the OP values. The results showed that the sources that highly contribute to the PM_2.5 mass (crustal dust and ammonium sulfate) were not the major sources contributing to the values of OP. Instead, 69 % of OP-AA_v and 62 % of OP-DTT_v values were explained by three local anthropogenic sources: Heavy Fuel Oil (HFO) combustion from a power plant, biomass burning, and road traffic emissions. As for the seasonal variations, higher OP-AA_v values were observed during winter compared to summer, while OP-DTT_v did not show any significant differences between the two seasons. The contribution of biomass burning during winter was 33 and 34 times higher compared to summer for OP-AA_v and OP-DTT_v, respectively. On the other hand, higher contributions were observed for HFO combustion during summer.