Investigating the use of secondary organic aerosol as seed particles in simulation chamber experiments - Discussion Paper

Jaqueline Hamilton, Rami Alfarra, Kevin Wyche, Martin Ward, Alistair Lewis, Gordon McFiggans, Nick Good, Paul Monks, Timo Carr, Iain White, Ruth Purvis

Research output: Contribution to journalArticlepeer-review

Abstract

The use of beta-caryophyllene secondary organic aerosol particles as seeds for smog
chamber simulations has been investigated. A series of experiments were carried
out in the Manchester photochemical chamber as part of the Aerosol Coupling in the
Earth System (ACES) project to study the effect of seed particles on the formation of
secondary organic aerosol (SOA) from limonene photo-oxidation. Rather than use a
conventional seed aerosol containing ammonium sulphate or diesel particles, a method
was developed to use in situ chamber generated seed particles from -caryophyllene
photo-oxidation, which were then diluted to a desired mass loading (in this case 4–13 μgm−3). Limonene was then introduced into the chamber and oxidised, with the formation of SOA seen as a growth in the size of oxidised organic seed particles from 150 to 325nm mean diameter. The effect of the partitioning of limonene oxidation products onto the seed aerosol was assessed using aerosol mass spectrometry during the experiment and the percentage of m/z 44, an indicator of degree of oxidation, increased from around 5 to 8%. The hygroscopicity of the aerosol also changed, with the growth factor for 200nm particles increasing from less than 1.05 to 1.25 at 90% RH. The detailed chemical composition of the limonene SOA could be extracted from the complex beta-caryophyllene matrix using two-dimensional gas chromatography (GC×GC) and liquid chromatography coupled to mass spectrometry. High resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FTICR-MS) was used to determine exact molecular formulae of the seed and the limonene modified aerosol. The average O:C ratio was seen to increase from 0.32 to 0.37 after limonene oxidation products had condensed onto the organic seed.
Original languageEnglish
Pages (from-to)25117-25151
JournalAtmospheric Chemistry and Physics Discussions
Volume10
DOIs
Publication statusPublished - 27 Oct 2010

Bibliographical note

This work is distributed under the Creative Commons Attribution 3.0 License.

Keywords

  • atmospheric science
  • secondary organic aerosol
  • particulate matter
  • biogenic
  • VOCs
  • oxidation
  • photochemistry

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