Gas phase reaction of OH radicals with (E)-β-farnesene at 296 ± 2 K: Rate coefficient and carbonyl products

The gas phase reaction of OH radicals with (E)-β-farnesene was investigated in a 3.91 m³ atmospheric simulation chamber at 296 ± 2 K and atmospheric pressure. The relative rate method was used to determine the reaction rate coefficient of (1.71 ± 0.21) × 10^-10 cm³ molecule^-1 s^-1. Gas phase carbonyl products were collected using a denuder sampling technique and analyzed with GC/MS following derivatization with O-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine (PFBHA). The reaction products detected were acetone, 4-oxopentanal, 4-methylenehex-5-enal, 6-methylhept-5-en-2-one and (E)-4-methyl-8-methylenedeca-4,9-dienal. A minor reaction product with MW 112 was tentatively identified as 4-oxohex-5-enal or 2-methylenepentanedial. A mechanism for the OH radical-initiated oxidation of (E)-β-farnesene is proposed, which accounts for all of the products observed in this study. The results of this work indicate that the atmospheric reaction of (E)-β-farnesene with OH radicals has a lifetime of around 1 h and is a potential source of the ubiquitous carbonyls, acetone, 4-oxopentanal and 6-methylhept-5-en-2-one in the atmosphere.