Determination of secondary organic aerosol products from the photooxidation of toluene and their implications in ambient PM2.5

Abstract

A laboratory study was carried out to investigate the secondary organic aerosol products from photooxidation of the aromatic hydrocarbon toluene. The laboratory experiments consisted of irradiating toluene/propylene/NOx/air mixtures in a smog chamber operated in the dynamic mode and collecting submicron secondary organic aerosol samples through a sampling train that consisted of an XAD denuder and a Zefluor™ filter. Oxidation products in the filter extracts were treated using O-(2,3,4,5,6,-pentafluorobenzyl)-hydroxylamine (PFBHA) to derivatize carbonyl groups followed by treatment with N, O-Bis(trimethylsilyl)-acetamide (BSTFA) to derivatize OH groups. The derivatized products were detected with a positive chemical ionization (CI) gas chromatography ion trap mass spectroscopy (GC-ITMS) system. The results of the GC-ITMS analyses were consistent with the previous studies that demonstrated the formation of multi-functional oxygenates. Denuder results showed that many of these same compounds were present in the gas, as well as, the particle phase. Moreover, evidence was found for a series of multifunctional acids produced as higher order oxidation products of the toluene/NOx system. Products having nearly the same mass spectrum were also found in the ambient environment using identical analytical techniques. These products having multiple acid and alcoholic-OH moieties have substantially lower volatility than previously reported SOA products of the toluene photooxidation and might serve as an indicator for aromatic oxidation in the ambient atmosphere.