Chemical analysis of aged benzene secondary organic aerosol using aerosol laser time-of-flight mass spectrometer

Secondary organic aerosol (SOA) from the photooxidation of aromatic compounds is a very complex mixture containing products with a different chemical nature that are dependent on aging processes. Aging of SOA particles formed from OH-initiated oxidation of benzene was investigated in a home-made smog chamber in this study. The chemical composition of aged benzene SOA particles were measured using aerosol laser time-of-flight mass spectrometer (ALTOFMS) coupled with Fuzzy C-Means (FCM) clustering algorithm. Experimental results showed that nitrophenol, dinitrophenol, nitrocatechol, dinitrocatechol, 6-oxo-2,4-hexadienoic acid, 2,4-hexadiendioic acid, 2,3-dihydroxy-6-oxo-4-hexenoic acid, 2,3-epoxy-4-hexendioic acid, 2,3-epoxy-4,5-dihydroxy-hexanedioic acid and high-molecular-weight (HMW) components were the predominant products in the aged particles. Compared to offline method such as liquid chromatography mass spectrometry (LC-MS) measurement, the real-time ALTOFMS detection approach coupled with the FCM data processing algorithm can make cluster analysis of SOA successfully and provide more information of products. The present results also indicate that benzene SOA aging proceeds through the oxidation of the internal double bond of ring-opened products, phenolic compounds, and acid-catalyzed heterogeneous reactions of carbonyl products. The possible reaction mechanisms leading to these aged products were also discussed and proposed.