Terpenylic acid and nine-carbon multifunctional compounds formed during the aging of β-pinene ozonolysis secondary organic aerosol

Recent field and laboratory studies suggest that forest aerosol particles contain more highly functionalized organic molecules than pinonic acid, a traditional molecular maker of secondary organic aerosol (SOA) particles. To investigate the reaction mechanisms during the aging of biogenic SOAs, the gases and particles formed from the ozonolysis of beta- and alpha-pinene were exposed to OH radicals in a laboratory chamber. The particle samples were collected before and after OH exposure for analysis by liquid chromatography-negative electrospray ionization time-of-flight mass spectrometry. Pinic acid and terpenylic acid were abundant products in both beta- and alpha-pinene ozonolysis SOA particles. Terpenylic acid and products with m/z 201.08 present in beta-pinene SOA particles increased upon exposing SOA to OH radicals, whereas 3-methyl-1,2,3-butanetricarboxylic acid present in alpha-pinene SOA particles increased upon exposing SOA to OH radicals. The products with m/z 201.08 were suggested to be C9H14O5 compounds. Similar C9H1405 compounds and terpenylic acid were also detected in SOA particles formed from the photooxidation of nopinone, a major first-generation product of beta-pinene ozonolysis. The OH initiated oxidation of nopinone will contribute to the formation of terpenylic acid and C9H1405 compounds during the aging of beta-pinene SOA. A formation mechanism for terpenylic acid via gas-phase diaterpenylic acid formation followed by self-dehydration in the condensed phase was suggested. (C) 2015 The Authors. Published by Elsevier Ltd.