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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 14 | Copyright
Atmos. Chem. Phys., 15, 7765-7776, 2015
https://doi.org/10.5194/acp-15-7765-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 16 Jul 2015

Research article | 16 Jul 2015

Phase partitioning and volatility of secondary organic aerosol components formed from α-pinene ozonolysis and OH oxidation: the importance of accretion products and other low volatility compounds

F. D. Lopez-Hilfiker1, C. Mohr1,7, M. Ehn2,3, F. Rubach3, E. Kleist4, J. Wildt4, Th. F. Mentel3, A. J. Carrasquillo5, K. E. Daumit5, J. F. Hunter5, J. H. Kroll5, D. R. Worsnop2,6, and J. A. Thornton1,2,3 F. D. Lopez-Hilfiker et al.
  • 1Department of Atmospheric Sciences, University of Washington, Seattle, WA, 98195, USA
  • 2Department of Physics, P.O. Box 64, 00014, University of Helsinki, Helsinki, Finland
  • 3Institute for Energy and Climate Research (IEK-8), Forschungszentrum Jülich, 52425 Jülich, Germany
  • 4Institute of Bio-Geosciences (IBG-2), Forschungszentrum Jülich, 52425 Jülich, Germany
  • 5Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
  • 6Center for Aerosol and Cloud Chemistry, Aerodyne Research, Inc., Billerica, MA, USA
  • 7Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology, 76344 Eggenstein-Leopoldshafen, Germany

Abstract. We measured a large suite of gas- and particle-phase multi-functional organic compounds with a Filter Inlet for Gases and AEROsols (FIGAERO) coupled to a high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS) developed at the University of Washington. The instrument was deployed on environmental simulation chambers to study monoterpene oxidation as a secondary organic aerosol (SOA) source. We focus here on results from experiments utilizing an ionization method most selective towards acids (acetate negative ion proton transfer), but our conclusions are based on more general physical and chemical properties of the SOA. Hundreds of compounds were observed in both gas and particle phases, the latter being detected by temperature-programmed thermal desorption of collected particles. Particulate organic compounds detected by the FIGAERO–HR-ToF-CIMS are highly correlated with, and explain at least 25–50 % of, the organic aerosol mass measured by an Aerodyne aerosol mass spectrometer (AMS). Reproducible multi-modal structures in the thermograms for individual compounds of a given elemental composition reveal a significant SOA mass contribution from high molecular weight organics and/or oligomers (i.e., multi-phase accretion reaction products). Approximately 50 % of the HR-ToF-CIMS particle-phase mass is associated with compounds having effective vapor pressures 4 or more orders of magnitude lower than commonly measured monoterpene oxidation products. The relative importance of these accretion-type and other extremely low volatility products appears to vary with photochemical conditions. We present a desorption-temperature-based framework for apportionment of thermogram signals into volatility bins. The volatility-based apportionment greatly improves agreement between measured and modeled gas-particle partitioning for select major and minor components of the SOA, consistent with thermal decomposition during desorption causing the conversion of lower volatility components into the detected higher volatility compounds.

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We measured a large suite organic compounds using a recently developed Filter Inlet for Gases and AEROsols (FIGAERO) coupled to a (HR-ToF-CIMS). The instrument was deployed on environmental simulation chambers to study monoterpene oxidation as a secondary organic aerosol (SOA) source. We find that approximately 50% of the detected particle phase mass is associated with compounds having effective vapor pressures 4, or more, orders of magnitude lower than commonly measured products.
We measured a large suite organic compounds using a recently developed Filter Inlet for Gases...
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