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Chemical analysis of SOA produced from the irradiation of a mixture of alpha/beta-farnesene/NOx was conducted in a 14.5 m(3) smog chamber. SOA collected on glass-fiber filters was solvent extracted, derivatized using BSTFA, and analyzed by GC MS. Gas-phase products were analyzed using a combination of GC-FID and GC MS. This analysis showed the occurrence of more than 30 SOA oxygenated species and more than 20 in the gas phase. The major SOA components measured include conjugated alpha-farnesene trienols, C3-C7 linear dicarboxylic acids, carbonyl compounds, and hydroxy/carbonyl/carboxylic compounds. In the gas phase, the main species identified were formaldehyde, glyoxal, methylglyoxal, acetone, 2,3-dimethyl-oxirane, 2(3H)-furanone, 2-butenedioic acid, 4-oxopentanal, 4-methylenehex-5-enal, and 6-methylhept-5-en-2-one. Proposed reaction schemes are provided for selected compounds. H-atom abstraction and OH addition in alpha-farnesene oxidation seem to play an important role via the formation of unsaturated radicals containing different numbers of delocalized electrons. Allylic hydrogen abstraction and hydroperoxyalkyl radical channels might play a key role in the oxidation of alpha-farnesene.

The contribution of farnesene SOA products to ambient PM2.5 was investigated by analyzing PM2.5 samples collected during SOAS 2013 field study at a site in Research Triangle Park (RTP), NC. The importance of these findings was supported by the occurrence of several organic species in both field and laboratory samples, suggesting the impact of farnesene on the ambient aerosol burden, mainly in areas where farnesene emissions are high. Although, pentanedioic acid and methylsuccinic acid appear to be candidate markers for farnesene SOA, additional chamber and mechanistic studies are required to estimate the contributions of farnesene to ambient SOA. (C) 2015 Published by Elsevier Ltd.