Influence of Peroxy Radical Fate on α-Pinene Photooxidation Gas-Phase Product Distributions
LESLY FRANCO DELOYA, Erik Helstrom, Hannah Kenagy, Manjula Canagaratna, Jesse Kroll, MIT
Abstract Number: 229
Working Group: Aerosol Chemistry
Abstract
Peroxy radical (RO2) fate is known to have a major influence on gas-phase oxidation product distributions, and hence on the yields and chemistry of secondary organic aerosol (SOA) formation. However, most SOA chamber studies conducted in the past have been carried out under limited peroxy radical conditions (e.g., “high NO” or “low NO”), which are unrepresentative of most RO2 conditions found in the atmosphere. In these chamber experiments we focus on the photooxidation of α-pinene across a range of peroxy radical reactivities (RO2 + NO, RO2 + HO2, RO2 + RO2, and RO2 isomerization), spanning the range of RO2 fates most important in the global atmosphere (as determined from chemical transport modeling). Experiments were carried out in a 7.5 m3 Teflon chamber, and an iodide chemical ionization mass spectrometer (I-CIMS) and proton transfer reaction mass spectrometer (PTR-MS) were used to measure gas-phase oxidation products. Product distributions are found to be strongly dependent on RO2 regime, with clear changes in the formation of organonitrates, carbonyl species, and fragmentation products. Product distributions are examined as a whole via Generalized Kendrick Analysis (GKA) and hierarchical clustering, revealing broad dependencies of product formation on RO2 chemistry. These results offer insights into how RO2 chemistry controls the formation of key species important to SOA (e.g., functionalization products, highly oxidized molecules), thus enabling improved descriptions of the oxidation mechanisms important for SOA formation.