AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Effect of Ozonolysis Chemistry on SOA Formation from Alkane Photooxidation
XUAN ZHANG, Katherine Schilling, Matthew Coggon, Rebecca Schwantes, Richard Flagan, John Seinfeld, California Institute of Technology
Abstract Number: 130 Working Group: Aerosol Chemistry
Abstract Long-chain alkanes, which are categorized as intermediate volatile organic compounds (IVOCs), are important source of secondary organic aerosol (SOA). The mechanism for the gas-phase OH-initiated oxidation of long-chain alkanes has been well documented. Particle-phase chemistry, however, has received less attention. Previous studies found that 1,4-hydroxycarbonyl, generated from the isomerization of alkoxy radicals, could undergo heterogeneous cyclization to form substituted dihydrofuran. Due to the presence of C=C bonds, substituted dihydrofuran is predicted to be highly reactive with OH and even more so with O3 and NO3. This work focuses on studying how substituted dihydrofuran formation and its subsequent reaction with ozone affects our current understanding of SOA formation from the photooxidation of long-chain alkanes. Experiments were carried out in the Caltech Environmental Chamber using n-dodecane as a target to investigate the difference in chemical composition of aerosols generated from “OH-oxidation dominating” vs. “ozonolysis dominating” environments. A detailed model incorporating the specific gas-phase photochemical mechanism, together with the heterogeneous formation of substituted dihydrofuran and its subsequent oxidation, was developed to evaluate the importance of this reaction channel and its impact on the SOA yield and oxidation state. We conclude that the ozonolysis of substituted dihydrofuran opens a reaction pathway that is not usually accessible to alkanes, expands the product distributions from alkane photochemistry, and possibly contributes significantly on the alkane SOA formation in the urban atmosphere.