AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Synchrotron Studies of the Heterogeneous Oxidation of Organic Aerosols
MICHAEL WARD, Kevin Wilson, Lawrence Berkeley National Laboratory
Abstract Number: 377 Working Group: Aerosol Chemistry
Abstract Understanding the relative importance of individual mechanistic pathways involved in the heterogeneous oxidation of organic aerosols offers the potential to tune such reactions toward favored outcomes. An important tool in attempting to disentangle the contribution of individual mechanistic pathways to the overall oxidation process is to study the kinetic evolution of aerosol oxidation products. While mass spectrometric techniques are typically used to study the kinetics of such heterogeneous oxidation reactions, the complex fragmentation patterns of large organic molecules can make it difficult to distinguish between positional isomers of the oxidation products. On the other hand, the exact identities of the oxidation products are typically determined using chromatographic techniques which do not readily lend themselves to kinetic studies.
Using the VUV light available at the Chemical Dynamics beamline of the Advanced Light Source synchrotron to ionize the oxidation products of model organic aerosols with minimal fragmentation, we are able to distinguish between different positional isomers of these oxidation products in real time using aerosol mass spectrometry. Consequently we have been able to determine the kinetic evolution of the separate positional isomers of oxidized aerosol species for the first time. These aerosol oxidation reactions are initiated by OH radicals and studied in a continuous flow stirred tank reactor (CFSTR) at atmospheric pressure. The experimental data indicate that, at low OH exposures, the OH radicals predominantly abstract hydrogen atoms from tertiary carbons, whilst the yields of positional isomers corresponding to attack at secondary carbons are seen to reach a maximum at higher OH exposures.