Abstract View
Gas and Particle-phase Highly Oxygenated Organic Molecules and Organic Nitrates from Chlorine-Initiated Photo-Oxidation of α-Pinene
CATHERINE MASOUD, Lea Hildebrandt Ruiz, University of Texas at Austin
Abstract Number: 504
Working Group: Aerosol Chemistry
Abstract
Measurements have shown that Cl can substantially affect particulate matter formation; yet, Cl-initiated SOA formation has not been studied in detail. In this work, we focus on Cl-initiated photo-oxidation of α-pinene leading to the formation of highly oxygenated organic molecules (HOMs) and organic nitrates in the vapor and particle phases.
Using a Filter Inlet for Gases and Aerosol mounted onto a Chemical Ionization Mass Spectrometer (FIGAERO-CIMS) operated in Iodide-mode, we identify and quantify HOMs in the gas and particle phases, which include chlorinated and nitrated HOMs. We report for the first time the gas- and particle-phase yields of HOMs from the α-pinene + Cl reaction under different experimental conditions, including different NOx levels, temperature, and precursor concentrations. (Previous work has focused on HOM yields in the vapor-phase alone.) We observe combined (vapor + particle phase) HOM monomer yields exceeding 5%, with particle-phase HOM yields up to six times higher than vapor-phase HOM yields. These high yields underscore the importance of HOM in the formation of organic aerosol.
We measure particulate organic nitrates (pONs) that are formed from different experimental conditions using an Aerosol Chemical Speciation Monitor (ACSM) and FIGAERO-CIMS. We use the FIGAERO-CIMS and a thermodenuder in tandem with the ACSM to explore the volatility of pONs formed. Data from both instruments are consistent with the particulate organic nitrates having higher vapor pressure than other oxygenated organics. We also compare the chemical composition of gas- and particle-phase products formed from the reactions of α-pinene + Cl versus α-pinene + OH under low and high NOx conditions.