Secondary Organic Aerosol Formation and Chemistry from the OH-Initiated Oxidation of Monofunctional C10 Species

Abstract

The formation of secondary organic aerosol (SOA), even from a simple hydrocarbon, is a complex, heterogeneous, multigenerational process involving hundreds of radical intermediate isomers and reaction pathways. Here, we compared the SOA generated from the reaction of the OH radical with five precursor species that differed in the identity of their primary functional group: n-decane, cyclodecane, 2-decanol, 2-decylnitrate, and 2-decanone. We compared results from smog chamber experiments and an explicit oxidation/gas-particle partitioning model of first-generation oxidation chemistry (Framework for 0-Dimensional Atmospheric Modeling–Washington Aerosol Module, F0AM-WAM) under two NO_x regimes: lower NO_x where RO₂ + HO₂ dominates and higher NO_x where RO₂ + NO dominates. Our results show that while functional group identity impacted the vapor pressures of the precursor species, this alone was unable to explain trends in experimental yields. Functional groups also directed the site of initiation with the OH radical and the propagation and termination reactions that follow, with the most significant differences noted for 2-decanol. SOA production was greater in the lower NO_x experiments for n-decane, 2-decanol, 2-decylnitrate, and 2-decanone due to production of the low volatility hydroperoxides and oxidized hydroxycarbonyls. Cyclodecane, however, produced more aerosol in higher NO_x experiments, potentially due to the enhanced formation of low volatility acetals or dimers in the presence of greater concentrations of nitric acid. Finally, we predicted that as much as 67% of the first-generation products may undergo subsequent oxidation to later-generation species. While model results from first-generation chemistry alone are unable to predict experimentally observed yields and chemistry, this work provides a foundation for the incorporation of additional (e.g., later-generation or heterogeneous oxidation chemistry, condensed-phase reactions, etc.) processes.