Effects of an Ether Group on the Mechanism, Products, and Nitrate and Secondary Organic Aerosol Yields for the Reaction of Dioctyl Ether with OH/NO_x

Products and mechanisms of atmospheric oxidation of volatile organic compounds (VOCs) are complex and depend on the VOC structure, oxidant, and oxidation regime. In addition to alkanes, alkenes, and aromatics, the major classes of hydrocarbons that are emitted to the atmosphere, oxygenated VOCs are also an important component of anthropogenic and biogenic emissions whose reactions can influence the formation of ozone and secondary organic aerosol. In this study, we investigated the effect of an ether group on the OH radical-initiated oxidation of dioctyl ether (DOE), a linear C₁₆ compound with an ether group located in the center of the carbon chain, under high NO_x conditions. Experiments were conducted in an environmental chamber, and gas- and particle-phase products were analyzed using gas and liquid chromatography, electron and chemical ionization mass spectrometry, infrared spectroscopy, and derivatization-spectrophotometry. Nitrate, hydroxynitrate, and hydroxycarbonyl ether products are analogous to those formed from the reaction of the corresponding alkane; however, the dominant product was octyl formate formed exclusively by reactions involving the ether group. Measured product yields were used with structure–activity relationships for OH and alkoxy radical reactions and literature branching ratios for the corresponding alkane reaction to determine the effect of the ether group on the branching ratio for nitrate vs alkoxy radical formation and to develop a simple model that predicted product yields in reasonable agreement with measurements. Compared to the corresponding alkane, the presence of the ether group increases OH reactivity, decreases the nitrate yield, and reduces the SOA yield by enhancing the formation of alkoxy radicals that decompose rather than isomerize to form low-volatility multifunctional products.