Oxidative potential apportionment of atmospheric PM1: A new approach combining high-sensitive online analysers for chemical composition and offline OP measurement technique.

Source apportionment models were widely used and/or atmospheric chemical processes. These technics are necessary to target the sources affecting air quality and to design effective mitigation strategies. More, the evaluation of the toxicity of airborne particulate matter gains interest as the PM concentrations classically measured appear insufficient to characterise the human health impact. Oxidative Potential (OP) measurement have recently been developed to quantify the PM capability to induce an oxidative imbalance in lungs. As a result, this measurement unit could be a better proxy than PM mass concentration to represent PM toxicity. In the present study, two source apportionment analyses were performed using Positive Matrix Factorization (PMF) from organic aerosol (OA) mass spectra measured at 15 min time resolution using a Time of Flight-Aerosol Chemical Speciation Monitor (ToF-ACSM) and from 19 trace elements measured on an hour basis using an online metals analyser (Xact). The field measurements were carried out in summer 2018. While it is common to perform PMF studies individually on ACSM and more recently on Xact datasets, here we used a two-step methodology leading to a complete PM₁ source apportionment. The outputs from both OA PMF and Xact PMF, the inorganic species concentrations from the ACSM and the black carbon (BC) fractions (fossil fuel and wood burning) measured using an Aethalometer (AE33) were gathered into a single dataset and subjected to a combined PMF analysis. In overall, 8 factors were identified, each of them corresponding to a more precise source than performing the previous single PMF analyses. The results show that besides the high contribution of secondary ammonium sulfate (28 %) and organic nitrate (19 %), about 50 % of PM₁ were originated from combustion processes (traffic, shipping, industrial, cooking and biomass burning emissions). Simultaneously, PM₁ filters were collected during the experimental period on a 4 hours sampling basis. On these filters, two acellular OP assays were measured (dithiothreitiol; OP_DTT and ascorbic acid; OP_AA) and an inversion method is applied on factors issued from all PMFs to assess contributions of the PM sources to the OP. This work highlights the sensitivity of OP_AA toward industrial and dust resuspension sources and those of OP_DTT toward secondary ammonium sulfate, shipping and biomass burning. [ABSTRACT FROM AUTHOR]