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Impacts of Functional Group Identity on SOA Yields and Kinetics
ANDREW HALLWARD-DRIEMEIER, Jonathan Hall, Amelia Schaeffer, Spence Katie, LeClerc Paul, Nicholas Whitcomb, Petra Baldwin, Nandini Seetharaman, Chris Avila, Anthony Carrasquillo, Williams College
Abstract Number: 479
Working Group: Aerosol Chemistry
Abstract
Much of the uncertainty in climate and air quality modeling derives from the challenges of modeling organic aerosol, particularly the Secondary Organic Aerosol (SOA) fraction which poses unique difficulties. SOA formation involves numerous possible oxidative pathways and multigenerational chemistry, further impeding modeling efforts. Initiation by the OH radical generally proceeds by H-abstraction, yielding an alkyl radical which couples with oxygen, generating an alkylperoxy radical, and finally reaction with NO to form an alkoxy radical. The alkoxy radical can then undergo a 1,5 H-abstraction and increase in oxidation state to form lower-volatility products that produce more SOA or fragment into smaller more volatile products that remain gaseous. Previous work has established that the structure of the alkoxy radical is key to determining branching ratios and therefore SOA yields and this work extends that analysis to the role of neighboring functional groups. Here, we take a structural approach to determine how varying the identity of a single functional group moiety influences the oxidative reaction pathways, especially with regards to the key fragmentation or abstraction step, and resulting properties of the products of different C-10 molecules: alkane, alkene, alkyne, alcohol, aldehyde, ketone, and halides. SOA was generated from each precursor VOC in a Teflon smog chamber via reaction with OH under low and high NOx conditions and the concentration of particles produced was measured. These results are discussed in the context of aerosol yields. Experimental data is supplemented with results of kinetics modeling of first-generation aerosol products and volatility measurements for each major product. By comparing the results from different precursor species we will provide new and valuable insight into the importance of functional group identity on SOA formation.