Secondary organic aerosol formation from cis-3-hexen-1-ol/NOx photo-oxidation: The roles of cis-3-hexen-1-ol concentration, illumination intensity, NOx and NH3

Abstract

Cis-3-Hexen-1-ol (cis-HXO) is an important green leaf volatile (GLV), and its photochemical oxidation is an important pathway to generate secondary organic aerosol (SOA). In this study, smog chamber experiments were carried out to investigate the effects of cis-HXO concentration, illumination intensity, and nitrogen oxides (NOX) and ammonia (NH3) levels on the formation of cis-HXO photo-oxidation SOA in the presence of NOX. The number concentration, mass concentration and yield of SOA under different influencing factors were determined using a scanning mobility particle sizer (SMPS) and a single photon ionization time-of-flight mass spectrometer (SPIMS). The experimental results demonstrated that stronger illumination intensity and higher cis-HXO concentration promoted particles formation. The SOA yield showed a good positive correlation with NOX concentration, especially under high NOX conditions, due to the fragmentation of alkoxy radicals during the reaction to form more polymerizable products as well as the presence of dinitrate and trinitrate, thus promoting the production of SOA. To our surprise, although the addition of NH3 promoted the formation of particles, it inhibited the growth of particles, and thus reducing the particles geometric mean diameter. The chemical components of cis-HXO photo-oxidation SOAs were also analyzed by a thermal-desorption gas chromatography mass spectrometry (TD-GC-MS). Based on the detected products, a reaction mechanism for the cis-HXO photo-oxidation was proposed. The experimental results confirm that cis-HXO is a significant global source of SOA which has a great reference significance for regional air quality prediction and more accurate modelling of global SOA generation.