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Long-chain alkanes, which can be categorized as intermediate volatilityorganic compounds, are an important source of secondary organicaerosol (SOA). Mechanisms for the gas-phase OH-initiated oxidation oflong-chain alkanes have been well documented; particle-phase chemistry,however, has received less attention. The δ-hydroxycarbonyl, which isgenerated from the isomerization of alkoxy radicals, can undergoheterogeneous cyclization and dehydration to form substituted dihydrofuran.Due to the presence of C=C bonds, the substituted dihydrofuran is predictedto be highly reactive with OH, and even more so with O3 and NO3,thereby opening a reaction pathway that is not usually accessible to alkanes.This work focuses on the role of substituted dihydrofuran formation and itssubsequent reaction with OH, and more importantly ozone, in SOA formationfrom the photooxidation of long-chain alkanes. Experiments were carried outin the Caltech Environmental Chamber using dodecane as a representativealkane to investigate the difference in aerosol composition generated from"OH-oxidation-dominating" vs. "ozonolysis-dominating" environments. Adetailed mechanism incorporating the specific gas-phase photochemistry,together with the heterogeneous formation of substituted dihydrofuran and itssubsequent gas-phase OH/O3 oxidation, is used to evaluate the importanceof this reaction channel in dodecane SOA formation. We conclude that (1) theformation of δ-hydroxycarbonyl and its subsequent heterogeneousconversion to substituted dihydrofuran is significant in the presence ofNOx; (2) the ozonolysis of substituted dihydrofuran dominates overthe OH-initiated oxidation under conditions prevalent in urban and rural air;and (3) a spectrum of highly oxygenated products with carboxylic acid, ester,and ether functional groups are produced from the substituted dihydrofuranchemistry, thereby affecting the average oxidation state of the SOA

Role of ozone in SOA formation from alkane photooxidation