Peroxy Radical and Product Formation in the Gas-Phase Ozonolysis of α-Pinene under Near-Atmospheric Conditions: Occurrence of an Additional Series of Peroxy Radicals O,O-C 10 H 15 O(O 2 ) y O 2 with y = 1-3.

Ozonolysis of α-pinene, C 10 H 16 , and other monoterpenes is considered to be one of the important chemical process in the atmosphere leading to condensable vapors, which are relevant to aerosol formation and, finally, for Earth's radiation budget. The formation of peroxy (RO 2 ) radicals, O,O-C 10 H 15 (O 2 ) x O 2 with x = 0-3, and closed-shell products has been probed from the ozonolysis of α-pinene for close to atmospheric reaction conditions. (The "O,O" in the chemical formulas indicates the two carbonyl groups formed in the ozonolysis.) An additional series of RO 2 radicals, O,O-C 10 H 15 O(O 2 ) y O 2 with y = 1-3, emerged in the presence of NO additions of (1.7-50) × 10 9 molecules cm -3 , whose formation can be explained via different processes starting from alkoxy (RO) radicals, such as the RO-driven autoxidation. The main closed-shell product is a substance with the composition C 10 H 16 O 3 , probably pinonic acid, obtained with a molar yield (lower limit) of 0.26 + 0.27 - 0.14 independent of NO. Total molar product yields accounted for up to 0.71 + 0.72 - 0.38 indicating reasonable detection sensitivity of the analytical technique applied. For the isomeric O,O-C 10 H 15 O 2 radicals, an average rate coefficient k (RO 2 + NO) = (1.5 ± 0.3) × 10 -11 cm 3 molecule -1 s -1 at 295 ± 2 K was determined. Product analysis showed a lowering in the formation of highly oxygenated organic molecules (HOMs) by a factor of ∼2.2 when adding 5 × 10 10 molecules cm -3 of NO. The comparison with former results revealed that total HOM suppression by NO in the α-pinene ozonolysis is slightly stronger than in the OH + α-pinene reaction.