ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-9-635-2009 Gas phase precursors to anthropogenic secondary organic aerosol: detailed observations of 1,3,5-trimethylbenzene photooxidation Wyche K. P. 1 Monks P. S. 1 Ellis A. M. 1 Cordell R. L. 1 Parker A. E. 1 Whyte C. 1 Metzger A. 2 Dommen J. 2 Duplissy J. 2 Prevot A. S. H. 2 Baltensperger U. 2 Rickard A. R. 3 Wulfert F. 4 Atmospheric Chemistry, Department of Chemistry, University of Leicester, Leicester, LE1 7RH, UK Laboratory of Atmospheric Chemistry, Paul Scherrer Institut, 5232, Villigen, Switzerland National Centre for Atmospheric Science, University of Leeds, Leeds, LS2 9JT, UK Division of Food Sciences, University of Nottingham, Sutton Bonington Campus, Loughborough, LE12 5RD, UK 27 01 2009 9 2 635 665 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/9/635/2009/acp-9-635-2009.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/9/635/2009/acp-9-635-2009.pdf

A series of photooxidation experiments were conducted in an atmospheric simulation chamber in order to investigate the oxidation mechanism and secondary organic aerosol (SOA) formation potential of the model anthropogenic gas phase precursor, 1,3,5-trimethylbenzene. Alongside specific aerosol measurements, comprehensive gas phase measurements, primarily by Chemical Ionisation Reaction Time-of-Flight Mass Spectrometry (CIR-TOF-MS), were carried out to provide detailed insight into the composition and behaviour of the organic components of the gas phase matrix during SOA formation. An array of gas phase organic compounds was measured during the oxidation process, including several previously unmeasured primary bicyclic compounds possessing various functional groups. Analysis of results obtained during this study implies that these peroxide bicyclic species along with a series of ring opening products and organic acids contribute to SOA growth. The effect of varying the VOC/NO<sub>x</sub> ratio on SOA formation was explored, as was the effect of acid seeding. It was found that low NO<sub>x</sub> conditions favour more rapid aerosol formation and a higher aerosol yield, a result that implies a role for organic peroxides in the nucleation process and SOA growth.

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