AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Characterization of Secondary Organic Aerosols Formed from the Photolysis of 2-Iodooctane/Air Mixtures Using 254nm Light
Iftikhar Awan, W. SEAN MCGIVERN, National Institute of Standards and Technology
Abstract Number: 726 Working Group: Aerosol Chemistry
Abstract The photolysis of alkyl iodides in air has been shown to be an excellent means to produce particles containing complex mixtures of oxygenated hydrocarbons in the laboratory. Previous work in our group has shown that photochemistry of peroxy radicals formed from the reaction of photolytically generated alkyl radicals with ambient oxygen has a significant impact on the condensed-phase product spectrum. This work focuses on the use of 2-octyl radicals formed via 254 nm photolysis of the C-I bond in 2-iodooctane in the presence of oxygen in a laminar flow cell. Condensed-phase oxidation products were collected on a microquartz filter and extracted in acetonitrile via sonication. The extract was chemically characterized using derivatization techniques to examine the hydroxyl and carbonyl functional group distributions with high-performance liquid chromatography (HPLC) coupled to UV-Vis absorption detection and ESI/MS-MS to selectively probe carbonyl- and hydroxyl-containing molecules. The observed carbonyl- and hydroxyl-substituted products are derived in part from peroxy-peroxy reactions, as expected in such a NO¬x-free environment. However, in addition, photochemically induced reactions, which include direct 2-octyl peroxy radical isomerization via internal H-abstraction and reverse dissociation to form 2-octyl radical and O2, play a key role. The complexity of the product spectrum is derived from these various channels, which scramble radical sites and further propagate the oxidation than expected in the absence of light. A comparison of the product distribution obtained from the present study with the condensed-phase product distribution of 1-octyl radical reactions with oxygen under the same experimental conditions will also be presented, particularly noting the differing carbonyl distributions that likely reflect the relative stabilities of the initial radical species and carbonyl products.