Aerosol particles have large implications for visibility, human health, and climate change. However, our ability to predict the chemical properties of aerosol is lacking due to uncertainties in how the organic fraction evolves over time. For example, bimolecular reactions of alkoxy radicals in the condensed phase represent potentially important pathways for the chemical evolution of aerosol particles. Radical chemistry in aerosol particles is commonly initiated through either direct photolysis or a heterogeneous hydrogen atom abstraction at the particle’s surface by an OH radical. The alkyl radicals formed undergo a series of reactions, ultimately forming an alkoxy radical. Alkoxy radicals undergo one of two major unimolecular pathways in the gas phase; fragmentation (forming more volatile compounds) or 1,5-H-atom isomerization (forming more highly oxidized, less volatile compounds). Due to much higher concentrations in the condensed phase, alkoxy radicals have been hypothesized to undergo bimolecular H-atom abstractions from neighboring aerosol components. The complex radical chemistry an individual organic molecule can undergo in the particle phase complicates the explicit observation of these bimolecular reactions in prior studies. Here, we isolate the formation of a single alkoxy radical by the direct photolysis of alkyl nitrites (RONO) to study (i.) the impact of its structure and (ii.) the composition of surrounding aerosol on bimolecular reaction facilitation. To measure the relevance of bimolecular H-atom abstractions in the absence of the 1,5 H-atom isomerization pathway, reactions of alkoxy radical compounds incapable of undergoing this alternate pathway (1.e., 2-butyl-nitrite, 2-pentyl-nitrite) are observed in several aerosol proxies (i.e., water, aldehydes, alcohols, etc.) pertinent to bimolecular H-atom abstraction (possessing relatively abstractable hydrogens). We measured product formation using GC/MS, through which bimolecular hydrogen atom abstractions could be detected through the formation of alcohol. This data provides greater insight into the relevance of bimolecular reactions to alkoxy radical chemistry in aerosol particles.<br/>

Improved understanding of the importance of bimolecular reactions of alkoxy radicals in organic aerosol

2019 Spring National Meeting

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