Abstract
Abstract. As part of the FORMES summer 2008 experiment, an Aerodyne compact time-of-flight aerosol mass spectrometer (cToF-AMS) was deployed at an urban background site in Marseille to investigate the sources and aging of organic aerosols (OA). France's second largest city and the largest port in the Mediterranean, Marseille, provides a locale that is influenced by significant urban industrialized emissions and an active photochemistry with very high ozone concentrations. Particle mass spectra were analyzed by positive matrix factorization (PMF2) and the results were in very good agreement with previous apportionments obtained using a chemical mass balance (CMB) approach coupled to organic markers and metals (El Haddad et al., 2011a). AMS/PMF2 was able to identify for the first time, to the best of our knowledge, the organic aerosol emitted by industrial processes. Even with significant industries in the region, industrial OA was estimated to contribute only ~ 5% of the total OA mass. Both source apportionment techniques suggest that oxygenated OA (OOA) constitutes the major fraction, contributing ~ 80% of OA mass. A novel approach combining AMS/PMF2 data with 14C measurements was applied to identify and quantify the fossil and non-fossil precursors of this fraction and to explicitly assess the related uncertainties. Results show with high statistical confidence that, despite extensive urban and industrial emissions, OOA is overwhelmingly non-fossil, formed via the oxidation of biogenic precursors, including monoterpenes. AMS/PMF2 results strongly suggest that the variability observed in the OOA chemical composition is mainly driven in our case by the aerosol photochemical age. This paper presents the impact of photochemistry on the increase of OOA oxygenation levels, formation of humic-like substances (HULIS) and the evolution of α-pinene SOA (secondary OA) components.
Highlights
Organic mixture gaoevroersnoel d(ObyA)mOiuscltiecpoalmenpeomSsiesdcsiiooenfnsacouhericgehsl,yredvyenrasmibliec tal organic aerosols (OA) mass
Applying a chemical mass balance (CMB) approach, we found that the OA was dominated by SOA, which based on 14C analyses was suggested to be heavily influenced by biogenic sources
We examined a 3-factor solution that yielded factors interpreted as hydrocarbon-like organic aerosol (HOA), semi-volatile oxygenated organic aerosol (SVOOA) and low volatility oxygenated organic aerosol (LVOOA), designations resulting from examining the factors’ mass spectra
Summary
Sampling for the FORMES 2008 summer field campaign was conducted from 30 June to 14 July 2008, at an urban background site in the downtown park “Cinq Avenues”, Marseille (43◦18 20 N, 5◦23 40 E, 64 m a.s.l.). The wind rose Sunset (operating at 8 L min−1) collected hourly PM2.5 meashows OA concentrations measured by the AMS as a function of surements of EC and OC. The former is a refractory fraction wind direction. In addition to synoptic air masses arriving from the Atlantic and the Mediterranean (see Fig. S1, Supplement), two regional wind patterns are common during the summer in Marseille: (i) the Mistral and (ii) a diurnal sea and land breeze cycle. For the analyses of major ions (NH+4 , SO24−, NO−3 ), water-soluble organic carbon and water-soluble humic-like substances (HULIS), sample fractions of 11.34 cm from high volume samples were extracted into 15 mL ultrapure Milli-Q water by 30 min short www.atmos-chem-phys.net/13/7875/2013/
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