Alkyl Substitution Alters Glycol Diether Peroxy Radical Fate and Suppresses Secondary Organic Aerosol Formation

Oxygenated volatile organic compounds (OVOCs) from volatile chemical products are emerging contributors to urban secondary organic aerosol (SOA) and ozone. Structural differences among OVOCS alter oxidation mechanisms and complicate our ability to predict air quality impacts. We examine the impact of alkyl substitution (branching) on OVOC fate during OH-initiated oxidation of two branched and two linear glycol diethers. Despite similar size and structural features, our observations show suppressed SOA yields from branched species relative to their linear counterparts, and reduced yields of lower volatility oxygenated gas-phase products. We use existing structure–activity relationships (SAR) in a simple kinetic model to examine how alkyl substitution alters the kinetics and mechanism of glycol diether oxidation. We find that peroxy radical (RO2) fate is a major control on product distributions from both branched and linear glycol diethers. Carbon-retaining hydroperoxy carbonyl products form through RO2 + HO2 reactions and RO2 H-shifts that are promoted by glycol diether functional groups. Alkyl substitution can decrease RO2 H-shift probability for both early and later generation RO2, leading to increased prevalence of bimolecular RO2 + NO pathways that promote alkoxy radical (RO) decomposition and suppress SOA formation. The governing role of functionalized RO2 fate on glycol diether oxidation, and resulting SOA production, likely applies to other classes of linear and branched OVOCs.