AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Control of Ozonolysis Kinetics and Aerosol Yield by Nuances in the Molecular Structure of Volatile Organic Compounds
REBECCA HARVEY, Giuseppe Petrucci, University of Vermont
Abstract Number: 104 Working Group: Aerosol Chemistry
Abstract Secondary organic aerosol (SOA) plays integral roles in climate and human health, yet there remains a limited understanding of the mechanisms that lead to its formation and ultimate fate. The disparity between modeled atmospheric SOA loadings and field measurements highlights the need for a more accurate representation of the molecular level interactions between SOA sources and oxidative pathways. Atmospheric models generally predict SOA loadings using structure activity relationships generalized to classes of SOA precursors. However, the kinetics and SOA forming potential of molecules are nuanced by seemingly minor structural differences in parent molecules.
We measured SOA yields and ozonolysis rate constants for several atmospherically relevant linear, cyclic and oxygenated C$_5-C$_7 alkenes whose molecular structure varies slightly in the site of unsaturation and/or the presence/position of functional groups. For 1-alkenes, SOA yield increased with carbon number but was also dependent on the position of the double bond, confirming previously reported trends. We also found greater SOA yields for cyclic compounds compared to their linear analogs, a comparison that has not explicitly been explored.
The presence of oxygenated functional groups influenced SOA yield and kinetics. For example, cis-3-hexene (3-HXN) had a lower SOA yield than its methyl ester- (cis-3-hexenyl acetate, CHA) and hydroxyl-substituted (cis-3-hexenol, HXL) analogs. The ozonolysis rate constant for 3-HXN was also 70% and 115% greater than CHA and HXL, respectively. The position and presence of oxygenated functional groups was found to impact SOA formation through steric and electronic effects.
We demonstrate the nuanced behavior of these ozonolysis reactions and discuss relationships between parent compound molecular structure and SOA yield and kinetics. We demonstrate that these key molecular features (location of double bond, presence and identity of substituents, linear vs cyclic geometry) must be considered to accurately model the impact of unsaturated VOCs in atmospheric oxidative cycles and SOA burden.