Formation of secondary organic aerosol from the styrene-NOx irradiation

Abstract

The formation of secondary organic aerosol (SOA) of the styrene-NOx-air under irradiation at a room temperature of (301±2) K has been investigated in a smog chamber. The effects of high relative humidity (72%) on the chemical components, number concentrations and yield of SOA have been investigated, respectively. The gas-phase products were determined to be formaldehyde, benzaldehyde, formic acid, CO, etc. SOA was collected on the polytetrafluoroethylene (PTFE) filter and analyzed with FTIR. The main products of SOA were found to be perbenzoyl nitrate, 2-nitrophenol, benzoic acid hydroxy-phenyl-methyl ester, peroxybenzoic acid and benzoic acid. It was found that at high relative humidity, gas-phase formic acid and benzoic acid are considerably increased, and the IR spectrum of SOA reveals a new absorption of benzoic acid, whereas the C=O absorbance from benzoic acid hydroxy-phenyl-methyl ester is decreased. This confirms the pathway of the reaction between H2O and Criegee biradical to produce benzoic acid hydroxy-phenyl-methyl ester. The SOA number concentration is decreased by about 36%~44% at high RH, whereas the SOA yield obtained from the mass collected by the PTFE membrane is increased by about 40% at high RH, compared with that at low RH, which demonstrates the increase in particle size at high RH.