Atmospheric aerosol particles have significant implications for visibility, human health, and climate. Our ability to predict aerosol formation and impact is limited by fundamental gaps in our understanding of the underlying chemistry. Among the least understood is the secondary organic aerosol (SOA) fraction, which forms from the oxidation of gas-phase, volatile organic compounds (VOC) and subsequent condensation of low-volatility products into the particle phase. The structure of a precursor VOC has been shown to be important in determining aerosol yield and composition, however to date no studies have systematically examined the role of VOC functional group identity in SOA formation. Here, we took a structural approach and varied the identities of functional groups on a precursor VOC under otherwise identical oxidation conditions to isolate this unknown aspect of aerosol formation. This chemistry is initiated via H-abstraction by an OH-radical to form an alkyl radical, which ultimately becomes an alkoxy radical after several radical chain propagation steps. This alkoxy radical is a key branching point within the SOA formation pathway because it can (i) undergo unimolecular 1,5-isomerization to form more oxidized, lower volatility products with higher SOA yields, or (ii)  fragment into smaller, higher volatility products with lower SOA yields. We hypothesized that the identity of precursor VOC functional groups determines the electronic and structural properties of this alkoxy radical intermediate, and therefore also the VOC’s preferred pathway and ultimate SOA yield. This hypothesis was tested using smog chamber experiments that simulate the chemistry of our atmosphere using a series of monofunctional, C-10 volatile organic compounds (aldehyde, ketone, alcohol, etc.). For each, aerosol yields were determined and LC-MS characterization of products provided insight into the pathways which were likely followed. This data represents an important contribution to improving our understanding of how we can predict aerosol yields by considering molecular structure.<br/>

Impact of VOC functional groups on secondary organic aerosol formation

2019 Spring National Meeting

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