Inter-annual variability of source contributions to PM 10 , PM 2.5 , and oxidative potential in an urban background site in the central mediterranean.

Airborne particulate matter (PM) is studied because of its effects on human health and climate change. PM long-term characterisation allows identifying trends and evaluating the outcomes of environmental protection policies. This work is aimed to study the inter-annual variability of PM and PM concentrations and chemical composition in an urban background site (Italy). A dataset of daily PM and PM was collected in the period 2016-2017, including the content of OC, EC, major water-soluble ions, main metals, and compared to a similar dataset collected in the period 2013-2014. Oxidative potential using DTT assay (dithiothreitol) was evaluated and expressed in DTT as 0.39 nmol/min·m in PM and 0.29 in PM nmol/min·m. PM source apportionment was computed using the EPA PMF5.0 model and source contributions compared with those of a previous dataset collected between 2013 and 2014. Multi linear regression analysis identified which source contributed (p < 0.05) to the oxidative potential of each size fraction. Inter-annual trends were more evident on PM with reductions of biomass burning contribution and increases in traffic contribution in the 2016-2017 period. Crustal contributions were similar for the two periods, in both size fractions. Carbonates were comparable in PM with a slight increase in PM. Sea spray decreased in PM. The DTT of PM peaked during cold periods, while, the DTT of the PM fraction peaked in summer, suggesting that different sources, with different seasonality, influence OP in the PM and PM fractions. Analysis showed that sea spray, crustal, and carbonates sources contribute ∼13.6% to DTT in PM and ∼62.4% to DTT in PM. Combustion sources (biomass burning and traffic) contribute to the majority of DTT (50.6%) in PM and contribute for ∼26% to DTT in PM. Secondary nitrate contributes to DTT in both fine and coarse fraction; secondary sulphate contribute to DTT in PM with negligible contributions to DTT in PM.