On the chemical nature of the oxygenated organic aerosol: implication in the formation and aging of α-pinene SOA in a Mediterranean environment, Marseille
1Aix-Marseille Univ., Laboratoire Chimie Environnement, 13331, Marseille cedex 03, France
2Université Lyon 1, Lyon, 69626, CNRS, UMR5256, IRCELYON, Institut de Recherches sur la Catalyse et l'Environnement de Lyon, Villeurbanne, 69626, France
3Universités Joseph Fourier-Grenoble 1-CNRS, UMR5183, Laboratoire de Glaciologie et Géophysique de l'Environnement, Saint Martin d'Hères, 38402, France
4Laboratoire des Sciences du Climat et de l'Environnement, CEA-CNRS-UVSQ-IPSL, Gif sur Yvette, 91191, France
*now at: Laboratory of Atmospheric Chemistry, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
**now at: INERIS, DRC/CARA/CIME, Parc Technologique Alata, BP2, Verneuil-en-Halatte, 60550, France
Abstract. Organic Aerosol (OA) measurements were conducted during summer 2008 at an urban background site, in Marseille, France's second city and the largest port in the Mediterranean, an urban industrialized environment known for its active photochemistry. PM2.5 was collected using high volume samplers and analyzed for elemental and organic carbon, major ions (NH4+, NO3− and SO42−), humic-like-substances, organic markers (i.e. primary tracers and α-pinene oxidation products), elemental composition and radiocarbon content (14C). The real-time chemical characterization of submicron particles was also achieved using a compact time of flight aerosol mass spectrometer. Positive matrix factorization conducted on the organic aerosol mass spectra matrix revealed four factors, including traffic emissions (hydrocarbon-like OA, HOA), industrial emissions, semi-volatile (SV-OOA) and low-volatile (LV-OOA) oxygenated organic aerosol (OOA) related to oxidation processes. The results obtained were in excellent agreement with chemical mass balance source apportionments conducted in conjunction with organic markers and elements. It appears that while primary emissions contributed only 22% to the total OA (of which 23% was associated with industrial processes), OOA constituted the overwhelming fraction. Radiocarbon measurements suggest that about 80% of this fraction was of non-fossil origin, assigned predominantly to biogenic secondary organic aerosol. Non-fossil carbon appears to especially dominate the LV-OOA fraction, an aged long-range-transported OOA, marginally affected by local anthropogenic SOA. We also examined the relation between OOA and α-pinene SOA obtained based on the levels of α-pinene oxidation products. α-pinene SOA showed good correlation with SV-OOA, suggesting that the compounds used for estimating α-pinene SOA appear to pertain mainly to the moderately oxidized fraction. In contrast, LV-OOA was found to be intimately related to HUmic LIke substances (HULIS), meaning that these two fractions arise from the same oxidation pathways and share a similar chemical composition (i.e. poly-carboxylic species). A thorough analysis of α-pinene individual oxidation products showed that aging can heavily impact their respective concentrations, as early generation products seem to decay with photochemistry when more oxidized compounds seem to be formed.