ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-941-2012 Determination of the biogenic secondary organic aerosol fraction in the boreal forest by NMR spectroscopy Finessi E. 1 10 Decesari S. 1 Paglione M. 1 Giulianelli L. 1 Carbone C. 1 Gilardoni S. 1 Fuzzi S. 1 Saarikoski S. 2 Raatikainen T. 2 8 Hillamo R. 2 Allan J. 3 Mentel Th. F. 4 Tiitta P. 5 9 Laaksonen A. 2 5 Petäjä T. 6 Kulmala M. 6 Worsnop D. R. 2 6 7 Facchini M. C. 1 Institute for Atmospheric Sciences and Climate (ISAC), National Research Council (CNR), Bologna, Italy Finnish Meteorological Institute (FMI), Helsinki, Finland National Centre for Atmospheric Science & School of Earth, Atmospheric & Environmental Sciences, The University of Manchester, Manchester, UK Institut für Chemie und Dynamik der Geosphäre, Forschungszentrum Jülich GmbH (FZJ-ICG-2), Jülich, Germany Department of Applied Physics, University of Eastern Finland (UEF), Kuopio, Finland Department of Physics, University of Helsinki, Finland Aerodyne Research, Inc. Billerica, MA, USA School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA Atmospheric Chemistry Research Group, North-West University, Potchefstroom, South Africa now at: Department of Chemistry, University of York, Heslington, York, YO10 5DD, UK 19 01 2012 12 2 941 959 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/12/941/2012/acp-12-941-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/941/2012/acp-12-941-2012.pdf

The study investigates the sources of fine organic aerosol (OA) in the boreal forest, based on measurements including both filter sampling (PM<sub>1</sub>) and online methods and carried out during a one-month campaign held in Hyytiälä, Finland, in spring 2007. Two aerosol mass spectrometers (Q-AMS, ToF-AMS) were employed to measure on-line concentrations of major non-refractory aerosol species, while the water extracts of the filter samples were analyzed by nuclear magnetic resonance (NMR) spectroscopy for organic functional group characterization of the polar organic fraction of the aerosol. AMS and NMR spectra were processed separately by non-negative factorization algorithms, in order to apportion the main components underlying the submicrometer organic aerosol composition and depict them in terms of both mass fragmentation patterns and functional group compositions. <br><br> The NMR results supported the AMS speciation of oxidized organic aerosol (OOA) into two main fractions, which could be generally labelled as more and less oxidized organics. The more oxidized component was characterized by a mass spectrum dominated by the <i>m/z</i> 44 peak, and in parallel by a NMR spectrum showing aromatic and aliphatic backbones highly substituted with oxygenated functional groups (carbonyls/carboxyls and hydroxyls). Such component, contributing on average 50% of the OA mass throughout the observing period, was associated with pollution outbreaks from the Central Europe. The less oxidized component was enhanced in concomitance with air masses originating from the North-to-West sector, in agreement with previous investigations conducted at this site. NMR factor analysis was able to separate two distinct components under the less oxidized fraction of OA. One of these NMR-factors was associated with the formation of terrestrial biogenic secondary organic aerosol (BSOA), based on the comparison with spectral profiles obtained from laboratory experiments of terpenes photo-oxidation. The second NMR factor associated with western air masses was linked to biogenic marine sources, and was enriched in low-molecular weight aliphatic amines. Such findings provide evidence of at least two independent sources originating biogenic organic aerosols in Hyytiälä by oxidation and condensation mechanisms: reactive terpenes emitted by the boreal forest and compounds of marine origin, with the latter relatively more important when predominantly polar air masses reach the site. <br><br> This study is an example of how spectroscopic techniques, such as proton NMR, can add functional group specificity for certain chemical features (like aromatics) of OA with respect to AMS. They can therefore be profitably exploited to complement aerosol mass spectrometric measurements in organic source apportionment studies.

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