Gas-Phase Oxidation Products From the Photooxidation of Fifteen Biogenic Terpenes

Biogenic emissions of terpene compounds influence atmospheric chemistry through the formation of tropospheric ozone and the production of secondary organic aerosol (SOA). We conducted photooxidation experiments at the Caltech Indoor Chamber Facility to examine the gas-phase products and secondary aerosol yields from isoprene, eight monoterpenes, four sesquiterpenes, and three oxygenated C10 terpenes. Terpenes were reacted with OH in the presence of NOx, with hydrocarbon to NOx ratios consistent with ratios typically observed in the ambient forested environments. The real-time formation of gas-phase oxidation products was monitored using a Proton Transfer Reaction Mass Spectrometer (PTR-MS), which identified compounds by their mass to charge ratio and showed multi-step oxidation pathways from these reactions. The photooxidation of terpenes resulted in the formation of numerous gas-phase oxidation products that were not observed from our previous ozonolysis experiments, as well as the formation of gas-phase organic nitrogen compounds. These gas-phase oxidation products can contribute to tropospheric chemistry through further oxidation reactions in the atmosphere, or may influence the biosphere through the deposition of organic nitrogen compounds downwind. Possible reaction mechanisms and products from the photooxidation of these terpene compounds will be presented, and the relevance of these laboratory experiments to recent observations of rapid within-canopy chemistry will be discussed.