The detection of low volatility organic compounds in the gas-phase from the OH-initiated oxidation of isoprene in chamber air and its relevance to organic aerosol production

Wednesday, 17 December 2014
Jordan Krechmer1, Matthew Mitchell Coggon2, John B Nowak3, Joel Kimmel3, Harald Stark1, Paola Massoli3, Lee Mauldin1, John Toulson Jayne3, John Crounse2, Tran B Nguyen4, Paul O Wennberg2, John Seinfeld2, Douglas R Worsnop3, Jose L Jimenez1 and Manjula R Canagaratna3, (1)University of Colorado at Boulder, Boulder, CO, United States, (2)California Institute of Technology, Pasadena, CA, United States, (3)Aerodyne Research Inc., Billerica, MA, United States, (4)California Institute of Technology, Division of Geological and Planetary Sciences, Pasadena, CA, United States
Low volatility organic compounds from the oxidation of isoprene have been observed under a variety of conditions during the FIXCIT atmospheric chamber study at Caltech in January of 2014. Data were obtained using a high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS) equipped with a nitrate-ion (NO3‑) source. The observed species, detected as clusters with the nitrate ion (m/z 62), range in elemental mass from approximately m/z 120-220 and span an elemental oxygen to elemental carbon ratio (O:C) range of 0.4 to 2.0. Using calibrations for simulant compounds obtained through subsequent laboratory studies, some of these highly oxidized isoprene products were quantified and their loadings and estimated production will be presented here. Ammonium sulfate aerosol seeds were injected into the chamber during several experiments, which enabled further investigation of the contribution of highly oxidized isoprene products to secondary organic aerosol (SOA) growth under a range of experimental conditions representative of the atmosphere where biogenic SOA has been shown to be an important contribution to submicron aerosol. Similar data were also obtained for oxidized species generated by the oxidation of semi-volatile isoprene products including isoprene hydroxyperoxide (ISOPOOH) and methacrolein (MACR) to further investigate mechanisms for isoprene oxidation and SOA formation. Measurements of these species’ uptake to chamber walls and seed aerosol will also be presented.