AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Quantitative Evidence of Ultraviolet Organic Peroxy Radical Photochemistry in a Photochemical Flow Cell
W. SEAN MCGIVERN, Joseph Klems, National Institute of Standards and Technology
Abstract Number: 330 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract The use of ultraviolet light in laboratory experiments to study processes that lead to organic aerosols in the atmospheric is extensive. Recently, we have provided qualitative evidence that peroxy radical photochemistry can play a significant role in determining the composition of organic aerosols formed in the presence of ultraviolet light. This work provides quantitative evidence for the relevance of these processes by examining the condensed-phase products formed in the extreme oxidation of dodecanoic acid by OH generated from the 254 nm photolysis of ozone in the presence of water. The products were analyzed using high-performance liquid chromatography (HPLC) with both ultraviolet (UV) absorption and tandem mass spectrometric (MS-MS) detection utilizing derivatization to specifically probe hydroxyl and carbonyl functional groups. The complex product spectrum for hydroxy-substituted species was broken in three distinct classes: singly substituted parent, multiply substituted parent, and products derived from decomposition of the parent. An a priori lumped kinetics model of the product distribution successfully reproduces the experimental product distribution only when photochemical processes, including both decomposition of the peroxy radical to form an alkyl radical and O$_2 and isomerization, are active. Two separate ultraviolet exposure conditions were also studied by shading a portion of the flow cell; modeling of this system, particularly in the low-exposure case, requires an understanding of the fate of alkyl hydroperoxides (R-OOH). The analysis of these compounds using HPLC/UV and MS-MS methods and their respective impact on measured product distributions from condensed-phase filter extracts will also be discussed.