The reaction of a simple alkane by OH proceeds through hydrogen abstraction and under ambient conditions leads to peroxy radical (RO2) formation. RO2 can further react by decomposing to smaller molecular weight products (fragmentation) via alkoxy radical formation or add oxygenated functional groups forming higher molecular weight products (functionalization). The ability to perturb these two pathways (functionalization vs. fragmentation) is critical for understanding the detailed reaction mechanism that controls atmospheric aging chemistry of particles. During organic-OH gas-phase oxidation both nitric oxide (NO) and sulfur dioxide (SO2) have been shown to enhance the fragmentation pathway by increasing alkoxy formation. Several studies have shown that NO increases alkoxy formation from peroxy radicals during organic aerosol oxidation; however, it is unknown whether enhanced alkoxy formation also occurs with SO2. The effect of NO and SO2 on the chemical mechanism of OH-initiated heterogeneous oxidation is obtained by measuring the heterogeneous rate constant and uptake coefficients of submicron particles composed of either squalane (C30H62, liquid), bis(2-ethylhexyl) sebacate (C26H50O4, liquid) or triacontane (C30H62, solid). Detailed kinetic measurements are made in a flow tube reactor using a vacuum ultraviolet (VUV) photoionization aerosol mass spectrometer. Oxidation products are identified from samples collected on quartz filters using thermal desorption two-dimensional chromatographic separation and ionization by either VUV (10.5 eV) or electron impact (70 eV), with detection by high resolution time of flight mass spectrometry (GCxGC-VUV/EI-HRTOFMS). For all model systems studied heterogeneous rate constants are enhanced by a factor of 3 and 2 for NO and SO2, respectively. The results from this work provide an experimentally-confirmed kinetic framework that could be used to model atmospheric aging mechanisms.

Heterogeneous oxidation of liquid and solid alkanes by OH in the presence and absence of NO or SO2

249th National Meeting (2015)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.