AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Effects of Hydroperoxyl-Radical-to-NO Ratio on SOA Formation from Aromatic Hydrocarbons in a Controlled Reactivity Urban Atmosphere
PENG WEIHAN, Mary Kacarab, William P. L. Carter, David R. Cocker III, University of California, Riverside
Abstract Number: 455 Working Group: Aerosol Chemistry
Abstract Secondary Organic Aerosol (SOA) formation from hydrocarbon precursors is typically predicted by using either two-product model or volatile basis set (VBS). Both models use two sets of aerosol yield parameters, low NOx and high NOx, which are estimated from environmental chamber studies. Given the fact that NO has significant effects on SOA, two scenarios of NO conditions are not sufficient to accurately represent the sensitivity of SOA to different NO levels. Thus, this work explores aerosol yield potential with a better resolution of NO concentration. Absolute NO condition or NO/VOC ratio is typically used as the index of oxidation level in environmental chamber; however, the relative level of NO to HO2 largely impacts SOA formation. The reactions of RO2 with both NO and HO2 are two important pathways of SOA formation with the gas-phase products from the RO2+HO2 pathway generally have lower volatility than that from RO2+NO reaction for aromatic hydrocarbon system. The ratio of NO to HO2 controls the branching ratio of these two reactions and thus determines secondary gas-phase products and their ability to partition to aerosol-phase. This work, instead of performing traditional single precursor chamber study, investigates the effects of NO and HO2 on SOA formation from m-xylene and 1, 2, 4 - TrimethylBenzene in a controlled reactivity system by adding a surrogate reactive organic gas mixture. All aromatic experiments were conducted in 90 m3 UCR/CECERT dual environmental reactors. HO2 is predicted using the SAPRC chemical mechanism. The correlation between SOA yield and HO2/NO is presented along with bulk SOA chemical composition via HR-ToF-AMS as a function of HO2/NO.