Formation of highly oxygenated organic molecules from aromatic compounds

Anthropogenic volatile organic compounds (AVOC) often dominate the urban atmosphere and consist to a large degree of aromatic hydrocarbons (ArHC), such as benzene, toluene, xylenes, and trimethylbenzenes, e.g. from handling and combustion of fuels. These compounds are important precursors for the formation of secondary organic aerosol. Here we show that 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 ArHC (benzene, toluene, o-/m-/pxylene, mesitylene (1,3,5-trimethylbenzene) and ethylbenzene), as well as two conjugated polycyclic ArHC (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 AVOC may contribute substantially to new particle formation events that have been detected in urban areas.