Gas and particulate products distribution from the photooxidation of α-humulene in the presence of NOx, natural atmospheric air and sunlight

The photooxidation of alpha-humulene in the presence of NOx, natural sunlight, and rural background air was investigated using a combination of gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography ( HPLC). Identification and quantification of gas and particulate reaction products were reported over the course of the reaction. The daytime photooxidation was carried out in a large outdoor smog chamber (190 m(3)). A wide range of ring retaining and ring opening products in the gas and particle phase are reported. On average, measured gas and particle phase products accounted for similar to44% of the reacted alpha-humulene carbon. Measurements show that a number of reaction products with low vapor pressures (e.g. 3-seco-alpha-humulone aldehyde, 7-seco-alpha-humulone aldehyde, alpha-humulal aldehyde, alpha-humulene 3-oxide or alpha-humulene 7-oxide, alpha-humulaic/alic acid isomers, and 3-seco-alpha-14-hydroxyhumulone aldehyde) were found in the early stage of the reaction and may play an important role in the early formation of secondary organic aerosol. A detailed mechanism is proposed to account for most products observed in this investigation.