Articles | Volume 17, issue 1
Atmos. Chem. Phys., 17, 117–141, 2017
Atmos. Chem. Phys., 17, 117–141, 2017

Research article 03 Jan 2017

Research article | 03 Jan 2017

Argon offline-AMS source apportionment of organic aerosol over yearly cycles for an urban, rural, and marine site in northern Europe

Carlo Bozzetti1, Yuliya Sosedova1, Mao Xiao1, Kaspar R. Daellenbach1, Vidmantas Ulevicius2, Vadimas Dudoitis2, Genrik Mordas2, Steigvilė Byčenkienė2, Kristina Plauškaitė2, Athanasia Vlachou1, Benjamin Golly3, Benjamin Chazeau1, Jean-Luc Besombes4, Urs Baltensperger1, Jean-Luc Jaffrezo3, Jay G. Slowik1, Imad El Haddad1, and André S. H. Prévôt1 Carlo Bozzetti et al.
  • 1Laboratory of Atmospheric Chemistry, Paul Scherrer Institute (PSI), 5232 Villigen-PSI, Switzerland
  • 2Department of Environmental Research, SRI Center for Physical Sciences and Technology, 02300 Vilnius, Lithuania
  • 3Université Grenoble Alpes, CNRS, LGGE, 38000 Grenoble, France
  • 4Université Savoie Mont-Blanc, LCME, 73000 Chambéry, France

Abstract. The widespread use of Aerodyne aerosol mass spectrometers (AMS) has greatly improved real-time organic aerosol (OA) monitoring, providing mass spectra that contain sufficient information for source apportionment. However, AMS field deployments remain expensive and demanding, limiting the acquisition of long-term datasets at many sampling sites. The offline application of aerosol mass spectrometry entailing the analysis of nebulized water extracted filter samples (offline-AMS) increases the spatial coverage accessible to AMS measurements, being filters routinely collected at many stations worldwide.

PM1 (particulate matter with an aerodynamic diameter < 1 µm) filter samples were collected during an entire year in Lithuania at three different locations representative of three typical environments of the southeast Baltic region: Vilnius (urban background), Rūgšteliškis (rural terrestrial), and Preila (rural coastal). Aqueous filter extracts were nebulized in Ar, yielding the first AMS measurements of water-soluble atmospheric organic aerosol (WSOA) without interference from air fragments. This enables direct measurement of the CO+ fragment contribution, whose intensity is typically assumed to be equal to that of CO2+. Offline-AMS spectra reveal that the water-soluble CO2+ : CO+ ratio not only shows values systematically > 1 but is also dependent on season, with lower values in winter than in summer.

AMS WSOA spectra were analyzed using positive matrix factorization (PMF), which yielded four factors. These factors included biomass burning OA (BBOA), local OA (LOA) contributing significantly only in Vilnius, and two oxygenated OA (OOA) factors, summer OOA (S-OOA) and background OOA (B-OOA), distinguished by their seasonal variability. The contribution of traffic exhaust OA (TEOA) was not resolved by PMF due to both low concentrations and low water solubility. Therefore, the TEOA concentration was estimated using a chemical mass balance approach, based on the concentrations of hopanes, specific markers of traffic emissions. AMS-PMF source apportionment results were consistent with those obtained from PMF applied to marker concentrations (i.e., major inorganic ions, OC / EC, and organic markers including polycyclic aromatic hydrocarbons and their derivatives, hopanes, long-chain alkanes, monosaccharides, anhydrous sugars, and lignin fragmentation products). OA was the largest fraction of PM1 and was dominated by BBOA during winter with an average concentration of 2 µg m−3 (53 % of OM), while S-OOA, probably related to biogenic emissions, was the prevalent OA component during summer with an average concentration of 1.2 µg m−3 (45 % of OM).

PMF ascribed a large part of the CO+ explained variability (97 %) to the OOA and BBOA factors. Accordingly, we discuss a new CO+ parameterization as a function of CO2+ and C2H4O2+ fragments, which were selected to describe the variability of the OOA and BBOA factors.

Short summary
In this study we present the offline-AMS source apportionment of the submicron organic aerosol (OA) sources conducted over 1 year at three locations in the south east Baltic region, which has so far received small attention. Offline-AMS enabled broadening the AMS spatial and temporal coverage, and provided a full characterization of the OA sources. Source apportionment results revealed that biomass burning and biogenic secondary emissions were the major OA sources during winter and summer.
Final-revised paper