Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
doi:10.5194/acp-2017-53
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
30 Jan 2017
Review status
A revision of this discussion paper was accepted for the journal Atmospheric Chemistry and Physics (ACP) and is expected to appear here in due course.
Particle Size Dependence of Biogenic Secondary Organic Aerosol Molecular Composition
Peijun Tu and Murray V. Johnston Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, USA
Abstract. Formation of secondary organic aerosol (SOA) is initiated by the oxidation of volatile organic compounds (VOCs) in the gas phase. Mass transfer to the particle phase is thought to occur primarily by a combination of condensation of non-volatile products and partitioning of semi-volatile products, though particle phase chemistry may also play a role if it transforms semi-volatile reactants into non-volatile products. In principle, changes in particle composition as a function of particle size allow the relative contributions of e.g. condensation (a surface-limited process) and particle phase reaction (a volume-limited process) to be distinguished. In this work, SOA was produced by β-pinene ozonolysis in a flow tube reactor. Aerosol exiting the reactor was size-selected with a differential mobility analyser, and individual particle sizes between 35 and 110 nm in diameter were characterized by on- and off- line mass spectrometry. Both the average oxygen-to-carbon (O / C) ratio and carbon oxidation state (OSc) were found to decrease with increasing particle size, while the relative signal intensity of oligomers increased with increasing particle size. These results are consistent with oligomer formation in the particle phase i.e. accretion reactions, which become more favoured as the surface-to-volume ratio of the particle decreases. Analysis of a series of polydisperse SOA samples showed similar dependencies: as the mass loading increased (and average surface-to-volume ratio decreased), the average O / C ratio and OSc decreased while the relative intensity of oligomer ions increased. The results illustrate the potential impact that particle phase chemistry can have on biogenic SOA formation and the particle size range where this chemistry becomes important.

Citation: Tu, P. and Johnston, M. V.: Particle Size Dependence of Biogenic Secondary Organic Aerosol Molecular Composition, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2017-53, in review, 2017.
Peijun Tu and Murray V. Johnston
Interactive discussionStatus: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version      Supplement - Supplement
 
RC1: 'Reviewer comments', Anonymous Referee #1, 25 Feb 2017 Printer-friendly Version 
AC1: 'Author Responses to Referee #1 Comments', Murray Johnston, 26 Mar 2017 Printer-friendly Version 
 
RC2: 'review', Anonymous Referee #2, 07 Apr 2017 Printer-friendly Version 
AC2: 'Author Response to Referee #2', Murray Johnston, 12 Apr 2017 Printer-friendly Version 
Peijun Tu and Murray V. Johnston
Peijun Tu and Murray V. Johnston

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Short summary
In this study, we determined the particle size-dependent molecular composition of secondary organic aerosol (SOA) that was produced from an important biogenic precursor. We find that the composition changes significantly with particle size, and these changes can be linked to changes in the chemical processes that contribute to particle growth. Measurements of this type can aid the modelling and prediction of SOA formation.
In this study, we determined the particle size-dependent molecular composition of secondary...
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