Articles | Volume 18, issue 3
https://doi.org/10.5194/acp-18-1909-2018
https://doi.org/10.5194/acp-18-1909-2018
Research article
 | 
09 Feb 2018
Research article |  | 09 Feb 2018

Formation of highly oxygenated organic molecules from aromatic compounds

Ugo Molteni, Federico Bianchi, Felix Klein, Imad El Haddad, Carla Frege, Michel J. Rossi, Josef Dommen, and Urs Baltensperger

Abstract. Anthropogenic volatile organic compounds (AVOCs) often dominate the urban atmosphere and consist to a large degree of aromatic hydrocarbons (ArHCs), such as benzene, toluene, xylenes, and trimethylbenzenes, e.g., from the handling and combustion of fuels. These compounds are important precursors for the formation of secondary organic aerosol. Here we show that the oxidation of aromatics with OH leads to a subsequent autoxidation chain reaction forming highly oxygenated molecules (HOMs) with an O : C ratio of up to 1.09. This is exemplified for five single-ring ArHCs (benzene, toluene, o-/m-/p-xylene, mesitylene (1,3,5-trimethylbenzene) and ethylbenzene), as well as two conjugated polycyclic ArHCs (naphthalene and biphenyl). We report the elemental composition of the HOMs and show the differences in the oxidation patterns of these ArHCs. A potential pathway for the formation of these HOMs from aromatics is presented and discussed. We hypothesize that AVOCs may contribute substantially to new particle formation events that have been detected in urban areas.

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Short summary
Anthropogenic volatile organic compounds often dominate the urban atmosphere and consist to a large degree of aromatics. These compounds are already known as important precursors for the formation of secondary organic aerosol. This study shows how the oxidation of aromatics with an OH radical leads to subsequent autoxidation chain reactions forming highly oxygenated molecules. We hypothesize that these may contribute substantially to new particle formation events detected in urban areas.
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