Smog chamber study of the effects of NOx and NH3 on the formation of secondary organic aerosols and optical properties from photo-oxidation of toluene

Abstract

Secondary organic aerosols (SOAs) have been receiving significant attention because of their significant impacts on air quality and human health. In this study, the influences of nitrogen oxides (NOx) and ammonia (NH3) on SOA formation from photooxidation of toluene was investigated in the Shanghai university smog chamber. The chemical and physical characteristics of gas-phase products and SOAs from toluene photo-oxidation were characterized using laboratory-developed single photon ionization time-of-flight mass spectrometry, single particle aerosol mass spectrometry, and cavity ring-down aerosol extinction albedo spectroscopy instruments. It was observed that increasing the initial nitrogen oxides ([NOx]0) under low-[NOx]0 conditions enhanced the SOA yield, while increasing [NOx]0 under high-[NOx]0 conditions suppressed the SOA yield. After adding NH3, the number concentration, average SOA diameter, and extinction and scattering coefficients showed an immediate and rapid increase due to the formation of significant amounts of condensable ammonium nitrate and nitrogen-containing (NOC) compounds. Moreover, a simplified reaction mechanism for the photooxidation of toluene initiated by the hydroxyl radical (OH) was believed to follow two reaction channels: minor H abstraction, and major OH addition, which continuously induced the subsequent reactions. The results of this study presented rapid analytical method for the joint use of a smog chamber with on-line analytical instruments to immediately characterize the effects of SOA formation, which will help in understanding the new particle formation and particle growth, and thus provides a new insight for in-depth understanding of the haze pollution in China.