29 Oct 2020

29 Oct 2020

Review status: this preprint is currently under review for the journal ACP.

Molecular characterization of gaseous and particulate oxygenated compounds at a remote site in Cape Corsica in the western Mediterranean basin

Vincent Michoud1, Elise Hallemans1,2, Laura Chiappini2,, Eva Leoz-Garziandia2, Aurélie Colomb3, Sébastien Dusanter4, Isabelle Fronval4, François Gheusi5, Jean-Luc Jaffrezo6, Thierry Léonardis4, Nadine Locoge4, Nicolas Marchand7, Stéphane Sauvage4, Jean Sciare8,9, and Jean-François Doussin1 Vincent Michoud et al.
  • 1LISA, UMR CNRS 7583, Université de Paris, Université Paris-Est-Créteil, Institut Pierre Simon Laplace (IPSL), Créteil, France
  • 2Institut National de l'Environnement Industriel et des Risques, Verneuil-en-Halatte, France
  • 3LaMP, CNRS UMR6016, Clermont Université, Université Blaise Pascal, Aubière, France
  • 4IMT Lille Douai, Univ. Lille, SAGE - Département Sciences de l'Atmosphère et Génie de l'Environnement, 59000 Lille, France
  • 5Laboratoire d’Aérologie, Université de Toulouse, CNRS, Toulouse, France
  • 6Université Grenoble Alpes, CNRS, IRD, IGE, 38000 Grenoble, France
  • 7Aix Marseille Univ, CNRS, LCE, Marseille, 13003, France
  • 8LSCE, CNRS-CEA-UVSQ, IPSL, Université Paris-Saclay, Gif-sur-Yvette, France
  • 9EEWRC, The Cyprus Institute, Nicosia, Cyprus
  • deceased

Abstract. The characterization of the molecular composition of organic carbon in both gaseous and aerosol is key to understand the processes involved in the formation and aging of secondary organic aerosol. Therefore a technique using active sampling on cartridges and filters and derivatization followed by analysis using a Thermal Desorption-Gas Chromatography/mass spectrometer (TD-GC/MS) has been used to study the molecular composition of organic carbon in both gaseous and aerosol phases during an intensive field campaign which took place in Corsica during the summer 2013: the ChArMEx (Chemistry and Aerosol Mediterranean Experiment) SOP1b (Special Observation Period 1B) campaign.

These measurements led to the identification of 51 oxygenated (carbonyl and or hydroxyl) compounds in the gaseous phase with concentrations comprised between 21 ng m−3 and 3900 ng m−3 and of 85 compounds in the particulate phase with concentrations comprised between 0.3 and 277 ng m−3. Comparisons of these measurements with collocated data using other techniques have been conducted showing fair agreement in general for most species except for glyoxal in the gas phase and malonic, tartaric, malic and succinic acids in the particle phase with disagreements that can reach up to a factor of 8 and 20 on average, respectively for the latter two acids.

Comparison between the sum of all compounds identified by TD-GC/MS in particle phase with the total Organic Matter (OM) mass reveal that 18 % of the total OM mass can be explained by the compounds measured by TD-GC/MS for the whole campaign. This number increase to 24 % of the total Water Soluble OM (WSOM) measured by PILS-TOC if we consider only the sum of the soluble compounds measured by TD-GC/MS. This highlights the non-negligible fraction of the OM mass identified by these measurements but also the relative important fraction of OM mass remaining unidentified during the campaign and therefore the complexity of characterizing exhaustively the Organic Aerosol (OA) molecular chemical composition.

The fraction of OM measured by TD-GC/MS is largely dominated by di-carboxylic acids which represents 49 % of the PM2.5 content detected and quantified by this technique. Other contributions to PM2.5 composition measured by TD-GC/MS are then represented by tri-carboxylic acids (15 %), alcohols (13 %), aldehydes (10 %), di-hydroxy-carboxylic acids (5 %), monocarboxylic acids and ketones (3 % each) and hydroxyl-carboxylic acids (2 %). These results highlight the importance of poly functionalized carboxylic acids for OM while the chemical processes responsible for their formation in both phases remain uncertain. While not measured by TD-GC/MS technique, HUmic-LIke Substances (HULIS) represent the most abundant identified species in the aerosol, contributing for 59 % of the total identified OM mass on average during the campaign.

14 compounds were detected and quantified in both phases allowing the calculation of experimental partitioning coefficient for these species. The comparison of these experimental partitioning coefficients with theoretical ones, estimated by three different models, reveals large discrepancies varying from 2 to 7 orders of magnitude. These results suggest that the supposed instantaneous equilibrium being established between gaseous and particulate phases assuming a homogeneous non-viscous particle phase is questionable.

Vincent Michoud et al.

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Vincent Michoud et al.

Vincent Michoud et al.


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Short summary
A multiphasic molecular characterization of oxygenated compounds has been carried out during the ChArMEx field campaign using offline analysis. It leads to the identification of 97 different compounds in the gas and aerosol phases and reveals the important contribution of organic acids to organic aerosol. In addition, comparison between experimental and theoretical partitioning coefficients revealed in most cases a large underestimation by the theory reaching 1 to 7 orders of magnitude.