Secondary Organic Aerosol from the Photooxidation of Aromatic Hydrocarbons: Molecular Composition

Abstract

Outdoor smog chamber photooxidations to determine the molecular composition of secondary organic aerosol (SOA) from toluene, m-xylene, p-xylene, ethylbenzene, m-ethyltoluene, p-ethyltoluene, and 1,2,4-trimethylbenzene in sunlight-irradiated hydrocarbon−NOx mixtures are reported. Gas-phase mechanisms leading to the observed products are proposed. Unsaturated anhydrides (2,5-furandione, 3-methyl-2,5-furandione, 3-ethyl-2,5-furandione) are predominant components of aerosol from all the aromatics, an observation that is consistent with gas-phase aromatic mechanisms involving ring fragmentation. Saturated anhydrides were also detected in significant quantities, which could result from the hydrogenation of the furandiones in sunlight in the particle phase.