Gas and Particulate Products Distribution from the Photooxidation of α-Humulene in the Presence of NOx, Natural Atmospheric Air and Sunlight

The photooxidation of -humulene in the presence of NO_x, 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 m³). 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 44% of the reacted -humulene carbon. Measurements show that a number of reaction products with low vapor pressures (e.g. 3-seco--humulone aldehyde, 7-seco--humulone aldehyde, -humulal aldehyde, -humulene 3-oxide or -humulene 7-oxide, -humulaic/alic acid isomers, and 3-seco--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.     

Emissions of Volatile Organic Compounds from Sunflower and Beech: Dependence on Temperature and Light Intensity

Emissions of volatile organic compounds (VOCs) from sunflower (Helianthus annuus L. cv. giganteus) were measured in a continuously stirred tank reactor. The compounds predominantly emitted from sunflower were: isoprene, the monoterpenes -pinene, -pinene, sabinene, 3-carene and limonene, an oxygenated terpene, not positively identified so far and the sesquiterpene -caryophyllene. Emission rates ranged from 0.8 x 10^–16 to 4.3 x 10 ^–15 mol cm^–2 s^–1 at a temperature of 25°C and at a light intensity of 820 µEm^–2 s^–1. A dependence of the emission rates on temperature as well as on light intensity was observed. The emission rates of -pinene, sabinene and thujene from beech (Fagus sylvatica L.) were also affected by temperature as well as by light intensity. Our results suggest that an emission algorithm for all compounds emitted from sunflower and beech has to consider temperature and light intensity simultaneously. The observations strongly indicate that the emissions of VOCs from sunflower and beech are in part closely coupled to the rate of biosynthesis and in part originate from diffusion out of pools. The emission rates can be described by an algorithm that combines the model given by Tingey and coworkers with the algorithm given by Guenther and coworkers after slight modification.