HR: 15:08h
AN: A43F-06    [Abstracts]
TI: Secondary organic aerosol formation from isoprene photooxidation
AU: * Kroll, J H
EM: kroll@caltech.edu
AF: California Institute of Technology, Departments of Environmental Science and Engineering and Chemical Engineering Mail Code 210-41, Pasadena, CA 91125 United States
AU: Ng, N L
EM: ng@caltech.edu
AF: California Institute of Technology, Departments of Environmental Science and Engineering and Chemical Engineering Mail Code 210-41, Pasadena, CA 91125 United States
AU: Murphy, S M
EM: shanem@caltech.edu
AF: California Institute of Technology, Departments of Environmental Science and Engineering and Chemical Engineering Mail Code 210-41, Pasadena, CA 91125 United States
AU: Flagan, R C
EM: flagan@caltech.edu
AF: California Institute of Technology, Departments of Environmental Science and Engineering and Chemical Engineering Mail Code 210-41, Pasadena, CA 91125 United States
AU: Seinfeld, J H
EM: seinfeld@caltech.edu
AF: California Institute of Technology, Departments of Environmental Science and Engineering and Chemical Engineering Mail Code 210-41, Pasadena, CA 91125 United States
AB: We report chamber studies of the formation of secondary organic aerosol (SOA) from the oxidation of isoprene (2-methyl-1,3-butadiene). Isoprene is the most abundant non-methane hydrocarbon emitted into the troposphere (source strength of ~500 Tg/year), so even small SOA yields may have a large impact on global SOA production. Reactions are carried out in Caltech's dual 28 m3 Teflon chambers, and aerosol growth is monitored by a differential mobility analyzer (DMA) and an Aerodyne time-of-flight aerosol mass spectrometer (AMS). Isoprene oxidation is initiated by the UV irradiation of isoprene in the presence of hydrogen peroxide, with NO added for high-NOx experiments. These conditions ensure that isoprene oxidation is initiated by reaction with the OH radical, with negligible interference from other oxidants (ozone, nitrate radicals, and O atoms). Aerosol growth is observed under both high-NOx and low-NOx conditions, at isoprene concentrations lower than measured in previous studies (down to 8 ppb). SOA yields are found to be in the range of 1-2%. Yields exhibit a complex dependence on NOx concentration, likely a result of changes in the chemistry of organic peroxy radicals. It is shown that condensable compounds are formed from further reactions of first-generation isoprene oxidation products; the rates and products of such gas-phase reactions are at present poorly understood. Additionally, measurements of SOA composition indicate that these products undergo reactions in the aerosol phase, leading to the formation of low-volatility oligomeric products.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0317 Chemical kinetic and photochemical properties
DE: 0368 Troposphere: constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005