AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Vapor Wall Deposition of Isoprene Photooxidation Products: RH, Mixing Status and Isomer Structure Effect
XUAN ZHANG, John Crounse, Alex Teng, Paul Wennberg, Richard Flagan, John Seinfeld, Caltech
Abstract Number: 70 Working Group: The Role of Water in Aerosol Chemistry
Abstract The wall-induced deposition of isoprene photooxidation products was investigated at a range of RHs (5 – 90 %) and different turbulent mixing status in the Caltech 24 m3 Teflon Chamber. Four species of which the deposition rate increases with increasing RHs were identified, as categorized as C4 – C5 carbonyls, epoxides, and nitrates. The lifetime of these organic vapors with respect to wall deposition was measured as low as ~ 1 h at 90% RH. We suggest that the hydrolysis reactions on the wall surface significantly enhance the deposition rate of these organic vapors, which otherwise are too volatile to partition substantially on the chamber wall. For the organic nitrate investigated here, the wall deposition rate varies with different structural isomers: the 2-methyl-2-nitroxybut-3-ene-1-ol isomer exhibits a much faster decay rate, which potentially results from the formation of stabilized tertiary alkyl radical via the unimolecular nucleophilic substitution (SN1) mechanism. The influence of the chamber mixing status on the measured vapor wall deposition rate is inappreciable in the RH range of 10 – 80%. In other words, the limiting process that governs the overall wall deposition rate of organic vapors investigated in this study is the wall accommodation, rather than gas-phase transport.